prog8/il65/codegen.py

"""
Programming Language for 6502/6510 microprocessors, codename 'Sick'
This is the assembly code generator (from the parse tree)

Written by Irmen de Jong (irmen@razorvine.net)
License: GNU GPL 3.0, see LICENSE
"""

import io
import re
import math
import datetime
import subprocess
import contextlib
from functools import partial
from typing import TextIO, Set, Union, List, Tuple, Callable
from .parse import ProgramFormat, ParseResult, Parser
from .symbols import Zeropage, DataType, ConstantDef, VariableDef, SubroutineDef, \
    STRING_DATATYPES, REGISTER_WORDS, REGISTER_BYTES, FLOAT_MAX_NEGATIVE, FLOAT_MAX_POSITIVE


class CodeError(Exception):
    pass


class CodeGenerator:
    BREAKPOINT_COMMENT_SIGNATURE = "~~~BREAKPOINT~~~"
    BREAKPOINT_COMMENT_DETECTOR = r".(?P<address>\w+)\s+ea\s+nop\s+;\s+{:s}.*".format(BREAKPOINT_COMMENT_SIGNATURE)

    def __init__(self, parsed: ParseResult) -> None:
        self.parsed = parsed
        self.generated_code = io.StringIO()
        self.p = partial(print, file=self.generated_code)
        self.previous_stmt_was_assignment = False
        self.cur_block = None    # type: ParseResult.Block

    def generate(self) -> None:
        print("\ngenerating assembly code")
        self.sanitycheck()
        self.header()
        self.initialize_variables()
        self.blocks()
        self.footer()

    def sanitycheck(self) -> None:
        # duplicate block names?
        all_blocknames = [b.name for b in self.parsed.blocks if b.name]
        unique_blocknames = set(all_blocknames)
        if len(all_blocknames) != len(unique_blocknames):
            for name in unique_blocknames:
                all_blocknames.remove(name)
            raise CodeError("there are duplicate block names", all_blocknames)
        # ZP block contains no code?
        for zpblock in [b for b in self.parsed.blocks if b.name == "ZP"]:
            if zpblock.label_names:
                raise CodeError("ZP block cannot contain labels")
            # can only contain code comments, or nothing at all
            if not all(isinstance(s, ParseResult.Comment) for s in zpblock.statements):
                raise CodeError("ZP block cannot contain code statements, only definitions and comments")

    def optimize(self) -> None:
        # optimize the generated assembly code
        pass

    def write_assembly(self, out: TextIO) -> None:
        out.write(self.generated_code.getvalue())

    def header(self) -> None:
        self.p("; code generated by il65.py - codename 'Sick'")
        self.p("; source file:", self.parsed.sourcefile)
        if self.parsed.with_sys:
            self.p("; output format:", self.parsed.format.value, " (with basic program SYS)")
        else:
            self.p("; output format:", self.parsed.format.value)
        self.p("; assembler syntax is for 64tasm")
        self.p(".cpu  '6502'\n.enc  'none'\n")
        if self.parsed.format == ProgramFormat.PRG:
            if self.parsed.with_sys:
                self.p("; ---- basic program with sys call ----")
                self.p("* = " + Parser.to_hex(self.parsed.start_address))
                year = datetime.datetime.now().year
                self.p("\t\t.word  (+), {:d}".format(year))
                self.p("\t\t.null  $9e, format(' %d ', _il65_sysaddr), $3a, $8f, ' il65 by idj'")
                self.p("+\t\t.word  0")
                self.p("_il65_sysaddr\t\t; assembly code starts here\n")
            else:
                self.p("; ---- program without sys call ----")
                self.p("* = " + Parser.to_hex(self.parsed.start_address) + "\n")
        if self.parsed.format == ProgramFormat.RAW:
            self.p("; ---- raw assembler program ----")
            self.p("* = " + Parser.to_hex(self.parsed.start_address) + "\n")

    @staticmethod
    def to_mflpt5(number: float) -> bytearray:
        # algorithm here https://sourceforge.net/p/acme-crossass/code-0/62/tree/trunk/ACME_Lib/cbm/mflpt.a
        number = float(number)
        if number < FLOAT_MAX_NEGATIVE or number > FLOAT_MAX_POSITIVE:
            raise OverflowError("floating point number out of 5-byte mflpt range", number)
        if number == 0.0:
            return bytearray([0, 0, 0, 0, 0])
        if number < 0.0:
            sign = 0x80000000
            number = -number
        else:
            sign = 0x00000000
        mant, exp = math.frexp(number)
        exp += 128
        if exp < 1:
            # underflow, use zero instead
            return bytearray([0, 0, 0, 0, 0])
        if exp > 255:
            raise OverflowError("floating point number out of 5-byte mflpt range", number)
        mant = sign | int(mant * 0x100000000) & 0x7fffffff
        return bytearray([exp]) + int.to_bytes(mant, 4, "big")

    @staticmethod
    def mflpt5_to_float(mflpt: bytearray) -> float:
        if mflpt == bytearray([0, 0, 0, 0, 0]):
            return 0.0
        exp = mflpt[0] - 128
        sign = mflpt[1] & 0x80
        number = 0x80000000 | int.from_bytes(mflpt[1:], "big")
        number = float(number) * 2**exp / 0x100000000
        return -number if sign else number

    def initialize_variables(self) -> None:
        must_save_zp = self.parsed.clobberzp and self.parsed.restorezp
        if must_save_zp:
            self.p("; save zp")
            self.p("\t\tsei")
            self.p("\t\tldx  #2")
            self.p("-\t\tlda  $00,x")
            self.p("\t\tsta  _il65_zp_backup-2,x")
            self.p("\t\tinx")
            self.p("\t\tbne  -")

        # Only the vars from the ZeroPage need to be initialized here,
        # the vars in all other blocks are just defined and pre-filled there.
        zpblocks = [b for b in self.parsed.blocks if b.name == "ZP"]
        if zpblocks:
            assert len(zpblocks) == 1
            zpblock = zpblocks[0]
            vars_to_init = [v for v in zpblock.symbols.iter_variables()
                            if v.allocate and v.type in (DataType.BYTE, DataType.WORD, DataType.FLOAT)]
            # @todo optimize sort order (sort on value first, then type, then blockname, then address/name)
            # (str(self.value) or "", self.blockname, self.name or "", self.address or 0, self.seq_nr)
            prev_value = 0  # type: Union[str, int, float]
            if vars_to_init:
                self.p("; init zp vars")
                self.p("\t\tlda  #0\n\t\tldx  #0")
                for variable in vars_to_init:
                    vname = zpblock.label + '.' + variable.name
                    vvalue = variable.value
                    if variable.type == DataType.BYTE:
                        if vvalue != prev_value:
                            self.p("\t\tlda  #${:02x}".format(vvalue))
                            prev_value = vvalue
                        self.p("\t\tsta  {:s}".format(vname))
                    elif variable.type == DataType.WORD:
                        if vvalue != prev_value:
                            self.p("\t\tlda  #<${:04x}".format(vvalue))
                            self.p("\t\tldx  #>${:04x}".format(vvalue))
                            prev_value = vvalue
                        self.p("\t\tsta  {:s}".format(vname))
                        self.p("\t\tstx  {:s}+1".format(vname))
                    elif variable.type == DataType.FLOAT:
                        raise CodeError("floats cannot be stored in the zp")
                self.p("; end init zp vars")
            else:
                self.p("\t\t; there are no zp vars to initialize")
        else:
            self.p("\t\t; there is no zp block to initialize")
        main_block_label = [b.label for b in self.parsed.blocks if b.name == "main"][0]
        if must_save_zp:
            self.p("\t\tjsr  {:s}.start\t\t; call user code".format(main_block_label))
            self.p("; restore zp")
            self.p("\t\tcld")
            self.p("\t\tphp\n\t\tpha\n\t\ttxa\n\t\tpha\n\t\tsei")
            self.p("\t\tldx  #2")
            self.p("-\t\tlda  _il65_zp_backup-2,x")
            self.p("\t\tsta  $00,x")
            self.p("\t\tinx")
            self.p("\t\tbne  -")
            self.p("\t\tcli\n\t\tpla\n\t\ttax\n\t\tpla\n\t\tplp")
            self.p("\t\trts")
            self.p("_il65_zp_backup\t\t.fill  254, 0")
        else:
            self.p("\t\tjmp  {:s}.start\t\t; call user code".format(main_block_label))

    def blocks(self) -> None:
        # if there's a <header> block, it always goes second
        for block in [b for b in self.parsed.blocks if b.name == "<header>"]:
            self.cur_block = block
            for s in block.statements:
                if isinstance(s, ParseResult.Comment):
                    self.p(s.text)
                else:
                    raise CodeError("header block cannot contain any other statements beside comments")
            self.p("\n")
        # if there's a Zeropage block, it always goes second
        for zpblock in [b for b in self.parsed.blocks if b.name == "ZP"]:
            self.cur_block = zpblock
            self.p("\n; ---- zero page block: '{:s}' ----\t\t; src l. {:d}\n".format(zpblock.sourceref.file, zpblock.sourceref.line))
            for s in zpblock.statements:
                if isinstance(s, ParseResult.Comment):
                    self.p(s.text)
                else:
                    raise CodeError("zp cannot contain any other statements beside comments")
            self.p("{:s}\t.proc\n".format(zpblock.label))
            self.generate_block_vars(zpblock)
            self.p("\t.pend\n")
        # make sure the main.start routine clears the decimal and carry flags as first steps
        block = self.parsed.find_block("main")
        statements = list(block.statements)
        for index, stmt in enumerate(statements):
            if isinstance(stmt, ParseResult.Label) and stmt.name == "start":
                asmlines = [
                    "\t\tcld\t\t\t; clear decimal flag",
                    "\t\tclc\t\t\t; clear carry flag",
                    "\t\tclv\t\t\t; clear overflow flag",
                ]
                statements.insert(index+1, ParseResult.InlineAsm(asmlines, 0))
                break
        block.statements = statements
        # generate
        for block in sorted(self.parsed.blocks, key=lambda b: b.address):
            if block.name in ("ZP", "<header>"):
                continue    # these blocks are already processed
            self.cur_block = block
            self.p("\n; ---- next block: '{:s}' ----\t\t; src l. {:d}\n".format(block.sourceref.file, block.sourceref.line))
            if block.address:
                self.p(".cerror * > ${0:04x}, 'block address overlaps by ', *-${0:04x},' bytes'".format(block.address))
                self.p("* = ${:04x}".format(block.address))
            self.p("{:s}\t.proc\n".format(block.label))
            self.generate_block_vars(block)
            subroutines = list(sub for sub in block.symbols.iter_subroutines() if sub.address is not None)
            if subroutines:
                self.p("\n; external subroutines")
                for subdef in subroutines:
                    assert subdef.sub_block is None
                    self.p("\t\t{:s} = {:s}".format(subdef.name, Parser.to_hex(subdef.address)))
                self.p("; end external subroutines")
            for stmt in block.statements:
                self.generate_statement(stmt)
            subroutines = list(sub for sub in block.symbols.iter_subroutines(True))
            if subroutines:
                self.p("\n; block subroutines")
                for subdef in subroutines:
                    assert subdef.sub_block is not None
                    self.p("{:s}\t\t; src l. {:d}".format(subdef.name, subdef.sourceref.line))
                    params = ", ".join("{:s} -> {:s}".format(p[0] or "<unnamed>", p[1]) for p in subdef.parameters)
                    returns = ",".join(sorted(subdef.return_registers))
                    clobbers = ",".join(sorted(subdef.clobbered_registers))
                    self.p("\t\t; params: {}\n\t\t; returns: {}   clobbers: {}"
                           .format(params or "-", returns or "-", clobbers or "-"))
                    cur_block = self.cur_block
                    self.cur_block = subdef.sub_block
                    for stmt in subdef.sub_block.statements:
                        self.generate_statement(stmt)
                    self.cur_block = cur_block
                    self.p("")
                self.p("; end external subroutines")
            self.p("\t.pend\n")

    def generate_block_vars(self, block: ParseResult.Block) -> None:
        consts = [c for c in block.symbols.iter_constants()]
        if consts:
            self.p("; constants")
            for constdef in consts:
                if constdef.type == DataType.FLOAT:
                    self.p("\t\t{:s} = {}".format(constdef.name, constdef.value))
                elif constdef.type in (DataType.BYTE, DataType.WORD):
                    self.p("\t\t{:s} = {:s}".format(constdef.name, Parser.to_hex(constdef.value)))     # type: ignore
                elif constdef.type in STRING_DATATYPES:
                    # a const string is just a string variable in the generated assembly
                    self._generate_string_var(constdef)
                else:
                    raise CodeError("invalid const type", constdef)
        mem_vars = [vi for vi in block.symbols.iter_variables() if not vi.allocate and not vi.register]
        if mem_vars:
            self.p("; memory mapped variables")
            for vardef in mem_vars:
                # create a definition for variables at a specific place in memory (memory-mapped)
                if vardef.type in (DataType.BYTE, DataType.WORD, DataType.FLOAT):
                    self.p("\t\t{:s} = {:s}\t; {:s}".format(vardef.name, Parser.to_hex(vardef.address), vardef.type.name.lower()))
                elif vardef.type == DataType.BYTEARRAY:
                    self.p("\t\t{:s} = {:s}\t; array of {:d} bytes".format(vardef.name, Parser.to_hex(vardef.address), vardef.length))
                elif vardef.type == DataType.WORDARRAY:
                    self.p("\t\t{:s} = {:s}\t; array of {:d} words".format(vardef.name, Parser.to_hex(vardef.address), vardef.length))
                elif vardef.type == DataType.MATRIX:
                    self.p("\t\t{:s} = {:s}\t; matrix {:d} by {:d} = {:d} bytes"
                           .format(vardef.name, Parser.to_hex(vardef.address), vardef.matrixsize[0], vardef.matrixsize[1], vardef.length))
                else:
                    raise CodeError("invalid var type")
        non_mem_vars = [vi for vi in block.symbols.iter_variables() if vi.allocate]
        if non_mem_vars:
            self.p("; normal variables")
            for vardef in non_mem_vars:
                # create a definition for a variable that takes up space and will be initialized at startup
                if vardef.type in (DataType.BYTE, DataType.WORD, DataType.FLOAT):
                    if vardef.address:
                        assert block.name == "ZP", "only ZP-variables can be put on an address"
                        self.p("\t\t{:s} = {:s}".format(vardef.name, Parser.to_hex(vardef.address)))
                    else:
                        if vardef.type == DataType.BYTE:
                            self.p("{:s}\t\t.byte  {:s}".format(vardef.name, Parser.to_hex(int(vardef.value))))
                        elif vardef.type == DataType.WORD:
                            self.p("{:s}\t\t.word  {:s}".format(vardef.name, Parser.to_hex(int(vardef.value))))
                        elif vardef.type == DataType.FLOAT:
                            self.p("{:s}\t\t.byte  ${:02x}, ${:02x}, ${:02x}, ${:02x}, ${:02x}"
                                   .format(vardef.name, *self.to_mflpt5(float(vardef.value))))
                        else:
                            raise CodeError("weird datatype")
                elif vardef.type in (DataType.BYTEARRAY, DataType.WORDARRAY):
                    if vardef.address:
                        raise CodeError("array or wordarray vars must not have address; will be allocated by assembler")
                    if vardef.type == DataType.BYTEARRAY:
                        self.p("{:s}\t\t.fill  {:d}, ${:02x}".format(vardef.name, vardef.length, vardef.value or 0))
                    elif vardef.type == DataType.WORDARRAY:
                        f_hi, f_lo = divmod(vardef.value or 0, 256)  # type: ignore
                        self.p("{:s}\t\t.fill  {:d}, [${:02x}, ${:02x}]\t; {:d} words of ${:04x}"
                               .format(vardef.name, vardef.length * 2, f_lo, f_hi, vardef.length, vardef.value or 0))
                    else:
                        raise CodeError("invalid datatype", vardef.type)
                elif vardef.type == DataType.MATRIX:
                    if vardef.address:
                        raise CodeError("matrix vars must not have address; will be allocated by assembler")
                    self.p("{:s}\t\t.fill  {:d}, ${:02x}\t\t; matrix {:d}*{:d} bytes"
                           .format(vardef.name,
                                   vardef.matrixsize[0] * vardef.matrixsize[1],
                                   vardef.value or 0,
                                   vardef.matrixsize[0], vardef.matrixsize[1]))
                elif vardef.type in STRING_DATATYPES:
                    self._generate_string_var(vardef)
                else:
                    raise CodeError("unknown variable type " + str(vardef.type))

    def _generate_string_var(self, vardef: Union[ConstantDef, VariableDef]) -> None:
        if vardef.type == DataType.STRING:
            # 0-terminated string
            self.p("{:s}\n\t\t.null  {:s}".format(vardef.name, self.output_string(str(vardef.value))))
        elif vardef.type == DataType.STRING_P:
            # pascal string
            self.p("{:s}\n\t\t.ptext  {:s}".format(vardef.name, self.output_string(str(vardef.value))))
        elif vardef.type == DataType.STRING_S:
            # 0-terminated string in screencode encoding
            self.p(".enc  'screen'")
            self.p("{:s}\n\t\t.null  {:s}".format(vardef.name, self.output_string(str(vardef.value), True)))
            self.p(".enc  'none'")
        elif vardef.type == DataType.STRING_PS:
            # 0-terminated pascal string in screencode encoding
            self.p(".enc  'screen'")
            self.p("{:s}\n\t\t.ptext  {:s}".format(vardef.name, self.output_string(str(vardef.value), True)))
            self.p(".enc  'none'")

    def generate_statement(self, stmt: ParseResult._AstNode) -> None:
        if isinstance(stmt, ParseResult.ReturnStmt):
            if stmt.a:
                if isinstance(stmt.a, ParseResult.IntegerValue):
                    self.p("\t\tlda  #{:d}".format(stmt.a.value))
                else:
                    raise CodeError("can only return immediate values for now")  # XXX
            if stmt.x:
                if isinstance(stmt.x, ParseResult.IntegerValue):
                    self.p("\t\tldx  #{:d}".format(stmt.x.value))
                else:
                    raise CodeError("can only return immediate values for now")  # XXX
            if stmt.y:
                if isinstance(stmt.y, ParseResult.IntegerValue):
                    self.p("\t\tldy  #{:d}".format(stmt.y.value))
                else:
                    raise CodeError("can only return immediate values for now")  # XXX
            self.p("\t\trts")
        elif isinstance(stmt, ParseResult.AugmentedAssignmentStmt):
            self.generate_augmented_assignment(stmt)
        elif isinstance(stmt, ParseResult.AssignmentStmt):
            self.generate_assignment(stmt)
        elif isinstance(stmt, ParseResult.Label):
            self.p("\n{:s}\t\t\t\t; src l. {:d}".format(stmt.name, stmt.lineno))
        elif isinstance(stmt, (ParseResult.InplaceIncrStmt, ParseResult.InplaceDecrStmt)):
            self.generate_incr_or_decr(stmt)
        elif isinstance(stmt, ParseResult.CallStmt):
            self.generate_call(stmt)
        elif isinstance(stmt, ParseResult.InlineAsm):
            self.p("\t\t; inline asm, src l. {:d}".format(stmt.lineno))
            for line in stmt.asmlines:
                self.p(line)
            self.p("\t\t; end inline asm, src l. {:d}".format(stmt.lineno))
        elif isinstance(stmt, ParseResult.Comment):
            self.p(stmt.text)
        elif isinstance(stmt, ParseResult.BreakpointStmt):
            # put a marker in the source so that we can generate a list of breakpoints later
            self.p("\t\tnop\t; {:s}  src l. {:d}".format(self.BREAKPOINT_COMMENT_SIGNATURE, stmt.lineno))
        else:
            raise CodeError("unknown statement " + repr(stmt))
        self.previous_stmt_was_assignment = isinstance(stmt, ParseResult.AssignmentStmt)

    def generate_incr_or_decr(self, stmt: Union[ParseResult.InplaceIncrStmt, ParseResult.InplaceDecrStmt]) -> None:
        if stmt.what.datatype == DataType.FLOAT:
            raise CodeError("incr/decr on float not yet supported")  # @todo support incr/decr on float
        else:
            assert type(stmt.howmuch) is int
        assert stmt.howmuch > 0
        if stmt.howmuch > 0xff:
            raise CodeError("only supports incr/decr by up to 255 for now")   # XXX
        is_incr = isinstance(stmt, ParseResult.InplaceIncrStmt)
        if isinstance(stmt.what, ParseResult.RegisterValue):
            if is_incr:
                if stmt.what.register == 'A':
                    self.p("\t\tclc")
                    self.p("\t\tadc  #{:d}".format(stmt.howmuch))
                elif stmt.what.register in REGISTER_BYTES:
                    if stmt.howmuch == 1:
                        self.p("\t\tin{:s}".format(stmt.what.register.lower()))
                    else:
                        self.p("\t\tpha")
                        self.p("\t\tt{:s}a".format(stmt.what.register.lower()))
                        self.p("\t\tclc")
                        self.p("\t\tadc  #{:d}".format(stmt.howmuch))
                        self.p("\t\tta{:s}".format(stmt.what.register.lower()))
                        self.p("\t\tpla")
                else:
                    raise CodeError("invalid incr/decr register")
            else:
                if stmt.what.register == 'A':
                    self.p("\t\tsec")
                    self.p("\t\tsbc  #{:d}".format(stmt.howmuch))
                elif stmt.what.register in REGISTER_BYTES:
                    if stmt.howmuch == 1:
                        self.p("\t\tde{:s}".format(stmt.what.register.lower()))
                    else:
                        self.p("\t\tpha")
                        self.p("\t\tt{:s}a".format(stmt.what.register.lower()))
                        self.p("\t\tsec")
                        self.p("\t\tsbc  #{:d}".format(stmt.howmuch))
                        self.p("\t\tta{:s}".format(stmt.what.register.lower()))
                        self.p("\t\tpla")
                else:
                    raise CodeError("invalid incr/decr register")
        elif isinstance(stmt.what, (ParseResult.MemMappedValue, ParseResult.IndirectValue)):
            what = stmt.what
            if isinstance(what, ParseResult.IndirectValue):
                if isinstance(what.value, ParseResult.IntegerValue):
                    r_str = what.value.name or Parser.to_hex(what.value.value)
                else:
                    raise CodeError("invalid incr indirect type", what.value)
            else:
                r_str = what.name or Parser.to_hex(what.address)
            if what.datatype == DataType.BYTE:
                if stmt.howmuch == 1:
                    self.p("\t\t{:s}  {:s}".format("inc" if is_incr else "dec", r_str))
                else:
                    self.p("\t\tpha")
                    self.p("\t\tlda  " + r_str)
                    if is_incr:
                        self.p("\t\tclc")
                        self.p("\t\tadc  #{:d}".format(stmt.howmuch))
                    else:
                        self.p("\t\tsec")
                        self.p("\t\tsbc  #{:d}".format(stmt.howmuch))
                    self.p("\t\tsta  " + r_str)
                    self.p("\t\tpla")
            elif what.datatype == DataType.WORD:
                if stmt.howmuch == 1:
                    if is_incr:
                        self.p("\t\tinc  " + r_str)
                        self.p("\t\tbne  +")
                        self.p("\t\tinc  {:s}+1".format(r_str))
                        self.p("+")
                    else:
                        self.p("\t\tpha")
                        self.p("\t\tlda  " + r_str)
                        self.p("\t\tbne  +")
                        self.p("\t\tdec  {:s}+1".format(r_str))
                        self.p("+\t\tdec  " + r_str)
                        self.p("\t\tpla")
                else:
                    raise CodeError("cannot yet incr/decr 16 bit memory by more than 1")   # @todo 16-bit incr/decr
            else:
                raise CodeError("cannot in/decrement memory of type " + str(what.datatype))
        else:
            raise CodeError("cannot in/decrement " + str(stmt.what))

    def generate_call(self, stmt: ParseResult.CallStmt) -> None:
        self.p("\t\t\t\t\t; src l. {:d}".format(stmt.lineno))
        if stmt.condition:
            assert stmt.is_goto
            if stmt.condition.lvalue:
                if stmt.condition.comparison_op:
                    self._generate_goto_conditional_comparison(stmt)
                else:
                    self._generate_goto_conditional_truthvalue(stmt)
            else:
                self._generate_goto_conditional_if(stmt)
        else:
            # unconditional goto or subroutine call.
            def branch_emitter(targetstr: str, is_goto: bool, target_indirect: bool) -> None:
                if is_goto:
                    if target_indirect:
                        self.p("\t\tjmp  ({:s})".format(targetstr))
                    else:
                        self.p("\t\tjmp  {:s}".format(targetstr))
                else:
                    assert not target_indirect
                    self.p("\t\tjsr  " + targetstr)
            self._generate_call_or_goto(stmt, branch_emitter)

    def _generate_goto_conditional_if(self, stmt):
        # a goto with just an if-condition, no condition expression
        def branch_emitter(targetstr: str, is_goto: bool, target_indirect: bool) -> None:
            assert is_goto and not stmt.condition.comparison_op
            ifs = stmt.condition.ifstatus
            if target_indirect:
                if ifs == "true":
                    self.p("\t\tbeq  +")
                    self.p("\t\tjmp  ({:s})".format(targetstr))
                    self.p("+")
                elif ifs in ("not", "zero"):
                    self.p("\t\tbne  +")
                    self.p("\t\tjmp  ({:s})".format(targetstr))
                    self.p("+")
                elif ifs in ("cc", "cs", "vc", "vs", "eq", "ne"):
                    if ifs == "cc":
                        self.p("\t\tbcs  +")
                    elif ifs == "cs":
                        self.p("\t\tbcc  +")
                    elif ifs == "vc":
                        self.p("\t\tbvs  +")
                    elif ifs == "vs":
                        self.p("\t\tbvc  +")
                    elif ifs == "eq":
                        self.p("\t\tbne  +")
                    elif ifs == "ne":
                        self.p("\t\tbeq  +")
                    self.p("\t\tjmp  ({:s})".format(targetstr))
                    self.p("+")
                elif ifs == "lt":
                    self.p("\t\tbcs  +")
                    self.p("\t\tjmp  ({:s})".format(targetstr))
                    self.p("+")
                elif ifs == "gt":
                    self.p("\t\tbcc  +")
                    self.p("\t\tbeq  +")
                    self.p("\t\tjmp  ({:s})".format(targetstr))
                    self.p("+")
                elif ifs == "ge":
                    self.p("\t\tbcc  +")
                    self.p("\t\tjmp  ({:s})".format(targetstr))
                    self.p("+")
                elif ifs == "le":
                    self.p("\t\tbeq  +")
                    self.p("\t\tbcs  ++")
                    self.p("+\t\tjmp  ({:s})".format(targetstr))
                    self.p("+")
                else:
                    raise CodeError("invalid if status " + ifs)
            else:
                if ifs == "true":
                    self.p("\t\tbne  " + targetstr)
                elif ifs in ("not", "zero"):
                    self.p("\t\tbeq  " + targetstr)
                elif ifs in ("cc", "cs", "vc", "vs", "eq", "ne"):
                    self.p("\t\tb{:s}  {:s}".format(ifs, targetstr))
                elif ifs == "lt":
                    self.p("\t\tbcc  " + targetstr)
                elif ifs == "gt":
                    self.p("\t\tbeq  +")
                    self.p("\t\tbcs  " + targetstr)
                    self.p("+")
                elif ifs == "ge":
                    self.p("\t\tbcs  " + targetstr)
                elif ifs == "le":
                    self.p("\t\tbcc  " + targetstr)
                    self.p("\t\tbeq  " + targetstr)
                else:
                    raise CodeError("invalid if status " + ifs)
        self._generate_call_or_goto(stmt, branch_emitter)

    def _generate_goto_conditional_truthvalue(self, stmt: ParseResult.CallStmt) -> None:
        # the condition is just the 'truth value' of the single value,
        # this is translated into assembly by comparing the argument to zero.
        def branch_emitter_mmap(targetstr: str, is_goto: bool, target_indirect: bool) -> None:
            assert is_goto and not stmt.condition.comparison_op
            assert stmt.condition.lvalue and not stmt.condition.rvalue
            assert not target_indirect
            assert stmt.condition.ifstatus in ("true", "not", "zero")
            branch, inverse_branch = ("bne", "beq") if stmt.condition.ifstatus == "true" else ("beq", "bne")
            cv = stmt.condition.lvalue
            assert isinstance(cv, ParseResult.MemMappedValue)
            cv_str = cv.name or Parser.to_hex(cv.address)
            if cv.datatype == DataType.BYTE:
                self.p("\t\tsta  " + Parser.to_hex(Zeropage.SCRATCH_B1))  # need to save A, because the goto may not be taken
                self.p("\t\tlda  " + cv_str)
                self.p("\t\t{:s}  {:s}".format(branch, targetstr))
                self.p("\t\tlda  " + Parser.to_hex(Zeropage.SCRATCH_B1))  # restore A
            elif cv.datatype == DataType.WORD:
                self.p("\t\tsta  " + Parser.to_hex(Zeropage.SCRATCH_B1))  # need to save A, because the goto may not be taken
                self.p("\t\tlda  " + cv_str)
                if stmt.condition.ifstatus == "true":
                    self.p("\t\t{:s}  {:s}".format(branch, targetstr))
                    self.p("\t\tlda  {:s}+1".format(cv_str))
                    self.p("\t\t{:s}  {:s}".format(branch, targetstr))
                    self.p("\t\tlda  " + Parser.to_hex(Zeropage.SCRATCH_B1))  # restore A
                else:
                    self.p("\t\t{:s}  +".format(inverse_branch, targetstr))
                    self.p("\t\tlda  {:s}+1".format(cv_str))
                    self.p("\t\t{:s}  {:s}".format(branch, targetstr))
                    self.p("+\t\tlda  " + Parser.to_hex(Zeropage.SCRATCH_B1))  # restore A
            else:
                raise CodeError("conditions cannot yet use other types than byte or word",  # @todo comparisons of other types
                                cv.datatype, str(cv), self.cur_block.sourceref.file, stmt.lineno)

        def branch_emitter_reg(targetstr: str, is_goto: bool, target_indirect: bool) -> None:
            assert is_goto and not stmt.condition.comparison_op
            assert stmt.condition.lvalue and not stmt.condition.rvalue
            assert not target_indirect
            assert stmt.condition.ifstatus in ("true", "not", "zero")
            branch, inverse_branch = ("bne", "beq") if stmt.condition.ifstatus == "true" else ("beq", "bne")
            line_after_branch = ""
            cv = stmt.condition.lvalue
            assert isinstance(cv, ParseResult.RegisterValue)
            if cv.register == 'A':
                self.p("\t\tcmp  #0")
            elif cv.register == 'X':
                self.p("\t\tcpx  #0")
            elif cv.register == 'Y':
                self.p("\t\tcpy  #0")
            else:
                if cv.register == 'AX':
                    line_after_branch = "+"
                    self.p("\t\tcmp  #0")
                    self.p("\t\t{:s}  {:s}".format(inverse_branch, line_after_branch))
                    self.p("\t\tcpx  #0")
                elif cv.register == 'AY':
                    line_after_branch = "+"
                    self.p("\t\tcmp  #0")
                    self.p("\t\t{:s}  {:s}".format(inverse_branch, line_after_branch))
                    self.p("\t\tcpy  #0")
                elif cv.register == 'XY':
                    line_after_branch = "+"
                    self.p("\t\tcpx  #0")
                    self.p("\t\t{:s}  {:s}".format(inverse_branch, line_after_branch))
                    self.p("\t\tcpy  #0")
                else:
                    raise CodeError("invalid register", cv.register)
            self.p("\t\t{:s}  {:s}".format(branch, targetstr))
            if line_after_branch:
                self.p(line_after_branch)

        def branch_emitter_indirect_cond(targetstr: str, is_goto: bool, target_indirect: bool) -> None:
            print("EMIT", stmt.target, stmt.condition, is_goto, target_indirect)
            assert is_goto and not stmt.condition.comparison_op
            assert stmt.condition.lvalue and not stmt.condition.rvalue
            assert stmt.condition.ifstatus in ("true", "not", "zero")
            cv = stmt.condition.lvalue.value   # type: ignore
            if isinstance(cv, ParseResult.RegisterValue):
                raise CodeError("indirect registers not yet supported")    # @todo indirect reg
            elif isinstance(cv, ParseResult.MemMappedValue):
                raise CodeError("memmapped indirect should not occur, use the variable without indirection")
            elif isinstance(cv, ParseResult.IntegerValue) and cv.constant:
                branch, inverse_branch = ("bne", "beq") if stmt.condition.ifstatus == "true" else ("beq", "bne")
                cv_str = cv.name or Parser.to_hex(cv.value)
                if cv.datatype == DataType.BYTE:
                    self.p("\t\tsta  " + Parser.to_hex(Zeropage.SCRATCH_B1))  # need to save A, because the goto may not be taken
                    self.p("\t\tlda  " + cv_str)
                    self.p("\t\t{:s}  {:s}".format(branch, targetstr))
                    self.p("\t\tlda  " + Parser.to_hex(Zeropage.SCRATCH_B1))  # restore A
                elif cv.datatype == DataType.WORD:
                    self.p("\t\tsta  " + Parser.to_hex(Zeropage.SCRATCH_B1))  # need to save A, because the goto may not be taken
                    self.p("\t\tlda  " + cv_str)
                    if stmt.condition.ifstatus == "true":
                        self.p("\t\t{:s}  {:s}".format(branch, targetstr))
                        self.p("\t\tlda  {:s}+1".format(cv_str))
                        self.p("\t\t{:s}  {:s}".format(branch, targetstr))
                        self.p("\t\tlda  " + Parser.to_hex(Zeropage.SCRATCH_B1))  # restore A
                    else:
                        self.p("\t\t{:s}  +".format(inverse_branch, targetstr))
                        self.p("\t\tlda  {:s}+1".format(cv_str))
                        self.p("\t\t{:s}  {:s}".format(branch, targetstr))
                        self.p("+\t\tlda  " + Parser.to_hex(Zeropage.SCRATCH_B1))  # restore A
                else:
                    raise CodeError("conditions cannot yet use other types than byte or word",  # @todo comparisons of other types
                                    cv.datatype, str(cv), self.cur_block.sourceref.file, stmt.lineno)
            else:
                raise CodeError("weird indirect type", str(cv))

        cv = stmt.condition.lvalue
        if isinstance(cv, ParseResult.RegisterValue):
            self._generate_call_or_goto(stmt, branch_emitter_reg)
        elif isinstance(cv, ParseResult.MemMappedValue):
            self._generate_call_or_goto(stmt, branch_emitter_mmap)
        elif isinstance(cv, ParseResult.IndirectValue):
            if isinstance(cv.value, ParseResult.RegisterValue):
                self._generate_call_or_goto(stmt, branch_emitter_indirect_cond)
            elif isinstance(cv.value, ParseResult.MemMappedValue):
                self._generate_call_or_goto(stmt, branch_emitter_indirect_cond)
            elif isinstance(cv.value, ParseResult.IntegerValue) and cv.value.constant:
                self._generate_call_or_goto(stmt, branch_emitter_indirect_cond)
            else:
                raise CodeError("weird indirect type", str(cv))
        else:
            raise CodeError("need register, memmapped or indirect value", str(cv))

    def _generate_goto_conditional_comparison(self, stmt: ParseResult.CallStmt) -> None:
        # the condition is lvalue operator rvalue
        raise NotImplementedError("no comparisons yet")  # XXX comparisons
        assert stmt.condition.ifstatus in ("true", "not", "zero")
        assert stmt.condition.lvalue != stmt.condition.rvalue  # so we know we actually have to compare different things
        lv, compare_operator, rv = stmt.condition.lvalue, stmt.condition.comparison_op, stmt.condition.rvalue
        if lv.constant and not rv.constant:
            # if lv is a constant, swap the whole thing around so the constant is on the right
            lv, compare_operator, rv = stmt.condition.swap()
        if isinstance(rv, ParseResult.RegisterValue):
            # if rv is a register, make sure it comes first instead
            lv, compare_operator, rv = stmt.condition.swap()
        if lv.datatype != DataType.BYTE or rv.datatype != DataType.BYTE:
            raise CodeError("can only generate comparison code for byte values for now")  # @todo compare non-bytes
        if isinstance(lv, ParseResult.RegisterValue):
            if isinstance(rv, ParseResult.RegisterValue):
                self.p("\t\tst{:s}  {:s}".format(rv.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                if lv.register == "A":
                    self.p("\t\tcmp  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                elif lv.register == "X":
                    self.p("\t\tcpx  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                elif lv.register == "Y":
                    self.p("\t\tcpy  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                else:
                    raise CodeError("wrong lvalue register")
            elif isinstance(rv, ParseResult.IntegerValue):
                rvstr = rv.name or Parser.to_hex(rv.value)
                if lv.register == "A":
                    self.p("\t\tcmp  #" + rvstr)
                elif lv.register == "X":
                    self.p("\t\tcpx  #" + rvstr)
                elif lv.register == "Y":
                    self.p("\t\tcpy  #" + rvstr)
                else:
                    raise CodeError("wrong lvalue register")
            elif isinstance(rv, ParseResult.MemMappedValue):
                rvstr = rv.name or Parser.to_hex(rv.address)
                if lv.register == "A":
                    self.p("\t\tcmp  " + rvstr)
                elif lv.register == "X":
                    self.p("\t\tcpx  #" + rvstr)
                elif lv.register == "Y":
                    self.p("\t\tcpy  #" + rvstr)
                else:
                    raise CodeError("wrong lvalue register")
            else:
                raise CodeError("invalid rvalue type in comparison", rv)
        elif isinstance(lv, ParseResult.MemMappedValue):
            assert not isinstance(rv, ParseResult.RegisterValue), "registers as rvalue should have been swapped with lvalue"
            if isinstance(rv, ParseResult.IntegerValue):
                self.p("\t\tsta  " + Parser.to_hex(Zeropage.SCRATCH_B1))  # need to save A, because the goto may not be taken
                self.p("\t\tlda  " + (lv.name or Parser.to_hex(lv.address)))
                self.p("\t\tcmp  #" + (rv.name or Parser.to_hex(rv.value)))
                line_after_goto = "\t\tlda  " + Parser.to_hex(Zeropage.SCRATCH_B1)  # restore A
            elif isinstance(rv, ParseResult.MemMappedValue):
                rvstr = rv.name or Parser.to_hex(rv.address)
                self.p("\t\tsta  " + Parser.to_hex(Zeropage.SCRATCH_B1))  # need to save A, because the goto may not be taken
                self.p("\t\tlda  " + (lv.name or Parser.to_hex(lv.address)))
                self.p("\t\tcmp  " + rvstr)
                line_after_goto = "\t\tlda  " + Parser.to_hex(Zeropage.SCRATCH_B1)  # restore A
            else:
                raise CodeError("invalid rvalue type in comparison", rv)
        else:
            raise CodeError("invalid lvalue type in comparison", lv)

    def _generate_call_or_goto(self, stmt: ParseResult.CallStmt, branch_emitter: Callable[[str, bool, bool], None]) -> None:
        def generate_param_assignments() -> None:
            self.p("; param assignment")  # XXX
            for assign_stmt in stmt.desugared_call_arguments:
                self.generate_assignment(assign_stmt)
            self.p("; param assignment done")  # XXX

        def generate_result_assignments() -> None:
            self.p("; result assignment")  # XXX
            for assign_stmt in stmt.desugared_output_assignments:
                self.generate_assignment(assign_stmt)
            self.p("; result assignment done")  # XXX

        def params_load_a() -> bool:
            for assign_stmt in stmt.desugared_call_arguments:
                for lv in assign_stmt.leftvalues:
                    if isinstance(lv, ParseResult.RegisterValue):
                        if lv.register == 'A':
                            return True
            return False

        def unclobber_result_registers(registers: Set[str], output_assignments: List[ParseResult.AssignmentStmt]) -> None:
            for a in output_assignments:
                for lv in a.leftvalues:
                    if isinstance(lv, ParseResult.RegisterValue):
                        if len(lv.register) == 1:
                            registers.discard(lv.register)
                        else:
                            for r in lv.register:
                                registers.discard(r)

        if stmt.target.name:
            symblock, targetdef = self.cur_block.lookup(stmt.target.name)
        else:
            symblock = None
            targetdef = None
        if isinstance(targetdef, SubroutineDef):
            if isinstance(stmt.target, ParseResult.MemMappedValue):
                targetstr = stmt.target.name or Parser.to_hex(stmt.address)
            else:
                raise CodeError("call sub target should be mmapped")
            if stmt.is_goto:
                generate_param_assignments()
                branch_emitter(targetstr, True, False)
                # no result assignments because it's a goto
                return
            clobbered = set()  # type: Set[str]
            if targetdef.clobbered_registers:
                if stmt.preserve_regs:
                    clobbered = targetdef.clobbered_registers
                    unclobber_result_registers(clobbered, stmt.desugared_output_assignments)
            with self.preserving_registers(clobbered, loads_a_within=params_load_a()):
                generate_param_assignments()
                branch_emitter(targetstr, False, False)
                generate_result_assignments()
            return
        if isinstance(stmt.target, ParseResult.IndirectValue):
            if stmt.target.name:
                targetstr = stmt.target.name
            elif stmt.address is not None:
                targetstr = Parser.to_hex(stmt.address)
            elif stmt.target.value.name:
                targetstr = stmt.target.value.name
            elif isinstance(stmt.target.value, ParseResult.RegisterValue):
                targetstr = stmt.target.value.register
            elif isinstance(stmt.target.value, ParseResult.IntegerValue):
                targetstr = stmt.target.value.name or Parser.to_hex(stmt.target.value.value)
            else:
                raise CodeError("missing name", stmt.target.value)
            if stmt.is_goto:
                # no need to preserve registers for a goto
                generate_param_assignments()
                if targetstr in REGISTER_WORDS:
                    self.p("\t\tst{:s}  {:s}".format(targetstr[0].lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                    self.p("\t\tst{:s}  {:s}".format(targetstr[1].lower(), Parser.to_hex(Zeropage.SCRATCH_B2)))
                    branch_emitter(Parser.to_hex(Zeropage.SCRATCH_B1), True, True)
                else:
                    branch_emitter(targetstr, True, True)
                # no result assignments because it's a goto
            else:
                # indirect call to subroutine
                preserve_regs = {'A', 'X', 'Y'} if stmt.preserve_regs else set()
                unclobber_result_registers(preserve_regs, stmt.desugared_output_assignments)
                with self.preserving_registers(preserve_regs, loads_a_within=params_load_a()):
                    generate_param_assignments()
                    # @todo optimize this with RTS_trick? https://wiki.nesdev.com/w/index.php/6502_assembly_optimisations#Use_Jump_tables_with_RTS_instruction_instead_of_JMP_indirect_instruction
                    if targetstr in REGISTER_WORDS:
                        if stmt.preserve_regs:
                            # cannot use zp scratch. This is very inefficient code!
                            print("warning: {:s}:{:d}: indirect register pair call, this is very inefficient"
                                  .format(self.cur_block.sourceref.file, stmt.lineno))
                            self.p("\t\tst{:s}  ++".format(targetstr[0].lower()))
                            self.p("\t\tst{:s}  +++".format(targetstr[1].lower()))
                            self.p("\t\tjsr  +")
                            self.p("\t\tjmp  ++++")
                            self.p("+\t\tjmp  (+)")
                            self.p("+\t\t.byte  0\t; lo")
                            self.p("+\t\t.byte  0\t; hi")
                            self.p("+")
                        else:
                            self.p("\t\tst{:s}  {:s}".format(targetstr[0].lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                            self.p("\t\tst{:s}  {:s}".format(targetstr[1].lower(), Parser.to_hex(Zeropage.SCRATCH_B2)))
                            self.p("\t\tjsr  +")
                            self.p("\t\tjmp  ++")
                            self.p("+\t\tjmp  ({:s})".format(Parser.to_hex(Zeropage.SCRATCH_B1)))
                            self.p("+")
                    else:
                        self.p("\t\tjsr  +")
                        self.p("\t\tjmp  ++")
                        self.p("+\t\tjmp  ({:s})".format(targetstr))
                        self.p("+")
                    generate_result_assignments()
        else:
            # call to a label or immediate address
            if stmt.target.name:
                targetstr = stmt.target.name
            elif stmt.address is not None:
                targetstr = Parser.to_hex(stmt.address)
            elif isinstance(stmt.target, ParseResult.IntegerValue):
                targetstr = stmt.target.name or Parser.to_hex(stmt.target.value)
            else:
                raise CodeError("missing name", stmt.target)
            if stmt.is_goto:
                # no need to preserve registers for a goto
                generate_param_assignments()
                branch_emitter(targetstr, True, False)
                # no result assignments because it's a goto
            else:
                preserve_regs = {'A', 'X', 'Y'} if stmt.preserve_regs else set()
                unclobber_result_registers(preserve_regs, stmt.desugared_output_assignments)
                with self.preserving_registers(preserve_regs, loads_a_within=params_load_a()):
                    generate_param_assignments()
                    branch_emitter(targetstr, False, False)
                    generate_result_assignments()

    def generate_augmented_assignment(self, stmt: ParseResult.AugmentedAssignmentStmt) -> None:
        # for instance: value += 3
        lvalue = stmt.leftvalues[0]
        rvalue = stmt.right
        self.p("\t\t\t\t\t; src l. {:d}".format(stmt.lineno))
        if isinstance(lvalue, ParseResult.RegisterValue):
            if isinstance(rvalue, ParseResult.IntegerValue):
                self._generate_aug_reg_int(lvalue, stmt.operator, rvalue)
            elif isinstance(rvalue, ParseResult.RegisterValue):
                self._generate_aug_reg_reg(lvalue, stmt.operator, rvalue)
            elif isinstance(rvalue, ParseResult.MemMappedValue):
                self._generate_aug_reg_mem(lvalue, stmt.operator, rvalue)
            else:
                raise CodeError("invalid rvalue for augmented assignment on register", str(rvalue))
        else:
            raise CodeError("augmented assignment only implemented for registers for now")  # XXX

    def _generate_aug_reg_mem(self, lvalue: ParseResult.RegisterValue, operator: str, rvalue: ParseResult.MemMappedValue) -> None:
        r_str = rvalue.name or Parser.to_hex(rvalue.address)
        if operator == "+=":
            if lvalue.register == "A":
                self.p("\t\tclc")
                self.p("\t\tadc  " + r_str)
            elif lvalue.register == "X":
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tclc")
                self.p("\t\tadc  " + r_str)
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tclc")
                self.p("\t\tadc  " + r_str)
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported register for aug assign", str(lvalue))  # @todo +=.word
        elif operator == "-=":
            if lvalue.register == "A":
                self.p("\t\tsec")
                self.p("\t\tsbc  " + r_str)
            elif lvalue.register == "X":
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tsec")
                self.p("\t\tsbc  " + r_str)
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tsec")
                self.p("\t\tsbc  " + r_str)
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported register for aug assign", str(lvalue))  # @todo -=.word
        elif operator == "&=":
            if lvalue.register == "A":
                self.p("\t\tand  " + r_str)
            elif lvalue.register == "X":
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tand  " + r_str)
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tand  " + r_str)
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported register for aug assign", str(lvalue))  # @todo &=.word
        elif operator == "|=":
            if lvalue.register == "A":
                self.p("\t\tora  " + r_str)
            elif lvalue.register == "X":
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tora  " + r_str)
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tora  " + r_str)
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported register for aug assign", str(lvalue))  # @todo |=.word
        elif operator == "^=":
            if lvalue.register == "A":
                self.p("\t\teor  " + r_str)
            elif lvalue.register == "X":
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\teor  " + r_str)
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\teor  " + r_str)
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported register for aug assign", str(lvalue))  # @todo ^=.word
        elif operator == ">>=":
            raise CodeError("can not yet shift a variable amount")  # XXX
        elif operator == "<<=":
            raise CodeError("can not yet shift a variable amount")  # XXX

    def _generate_aug_reg_int(self, lvalue: ParseResult.RegisterValue, operator: str, rvalue: ParseResult.IntegerValue) -> None:
        r_str = rvalue.name or Parser.to_hex(rvalue.value)
        if operator == "+=":
            if lvalue.register == "A":
                self.p("\t\tclc")
                self.p("\t\tadc  #" + r_str)
            elif lvalue.register == "X":
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tclc")
                self.p("\t\tadc  #" + r_str)
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tclc")
                self.p("\t\tadc  #" + r_str)
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported register for aug assign", str(lvalue))  # @todo +=.word
        elif operator == "-=":
            if lvalue.register == "A":
                self.p("\t\tsec")
                self.p("\t\tsbc  #" + r_str)
            elif lvalue.register == "X":
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tsec")
                self.p("\t\tsbc  #" + r_str)
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tsec")
                self.p("\t\tsbc  #" + r_str)
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported register for aug assign", str(lvalue))  # @todo -=.word
        elif operator == "&=":
            if lvalue.register == "A":
                self.p("\t\tand  #" + r_str)
            elif lvalue.register == "X":
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tand  #" + r_str)
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tand  #" + r_str)
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported register for aug assign", str(lvalue))  # @todo &=.word
        elif operator == "|=":
            if lvalue.register == "A":
                self.p("\t\tora  #" + r_str)
            elif lvalue.register == "X":
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tora  #" + r_str)
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tora  #" + r_str)
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported register for aug assign", str(lvalue))  # @todo |=.word
        elif operator == "^=":
            if lvalue.register == "A":
                self.p("\t\teor  #" + r_str)
            elif lvalue.register == "X":
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\teor  #" + r_str)
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\teor  #" + r_str)
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported register for aug assign", str(lvalue))  # @todo ^=.word
        elif operator == ">>=":
            if rvalue.value != 1:
                raise CodeError("can only shift 1 bit for now")  # XXX
            if lvalue.register == "A":
                self.p("\t\tlsr  a")
            elif lvalue.register == "X":
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tlsr  a")
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tlsr  a")
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported register for aug assign", str(lvalue))  # @todo >>=.word
        elif operator == "<<=":
            if rvalue.value != 1:
                raise CodeError("can only shift 1 bit for now")  # XXX
            if lvalue.register == "A":
                self.p("\t\tasl  a")
            elif lvalue.register == "X":
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tasl  a")
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tasl  a")
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported register for aug assign", str(lvalue))  # @todo <<=.word

    def _generate_aug_reg_reg(self, lvalue: ParseResult.RegisterValue, operator: str, rvalue: ParseResult.RegisterValue) -> None:
        if operator == "+=":
            if rvalue.register not in REGISTER_BYTES:
                raise CodeError("unsupported rvalue register for aug assign", str(rvalue))  # @todo +=.word
            if lvalue.register == "A":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tclc")
                self.p("\t\tadc  " + Parser.to_hex(Zeropage.SCRATCH_B1))
            elif lvalue.register == "X":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tclc")
                self.p("\t\tadc  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tclc")
                self.p("\t\tadc  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported lvalue register for aug assign", str(lvalue))  # @todo +=.word
        elif operator == "-=":
            if rvalue.register not in REGISTER_BYTES:
                raise CodeError("unsupported rvalue register for aug assign", str(rvalue))  # @todo -=.word
            if lvalue.register == "A":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tsec")
                self.p("\t\tsbc  " + Parser.to_hex(Zeropage.SCRATCH_B1))
            elif lvalue.register == "X":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tsec")
                self.p("\t\tsbc  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tsec")
                self.p("\t\tsbc  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported lvalue register for aug assign", str(lvalue))  # @todo -=.word
        elif operator == "&=":
            if rvalue.register not in REGISTER_BYTES:
                raise CodeError("unsupported rvalue register for aug assign", str(rvalue))  # @todo &=.word
            if lvalue.register == "A":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tand  " + Parser.to_hex(Zeropage.SCRATCH_B1))
            elif lvalue.register == "X":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tand  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tand  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported lvalue register for aug assign", str(lvalue))  # @todo &=.word
        elif operator == "|=":
            if rvalue.register not in REGISTER_BYTES:
                raise CodeError("unsupported rvalue register for aug assign", str(rvalue))  # @todo |=.word
            if lvalue.register == "A":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tora  " + Parser.to_hex(Zeropage.SCRATCH_B1))
            elif lvalue.register == "X":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tora  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tora  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported lvalue register for aug assign", str(lvalue))  # @todo |=.word
        elif operator == "^=":
            if rvalue.register not in REGISTER_BYTES:
                raise CodeError("unsupported rvalue register for aug assign", str(rvalue))  # @todo ^=.word
            if lvalue.register == "A":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\teor  " + Parser.to_hex(Zeropage.SCRATCH_B1))
            elif lvalue.register == "X":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\teor  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\teor  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported lvalue register for aug assign", str(lvalue))  # @todo ^=.word
        elif operator == ">>=":
            if rvalue.register not in REGISTER_BYTES:
                raise CodeError("unsupported rvalue register for aug assign", str(rvalue))  # @todo >>=.word
            if lvalue.register == "A":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tlsr  " + Parser.to_hex(Zeropage.SCRATCH_B1))
            elif lvalue.register == "X":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tlsr  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tlsr  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported lvalue register for aug assign", str(lvalue))  # @todo >>=.word
        elif operator == "<<=":
            if rvalue.register not in REGISTER_BYTES:
                raise CodeError("unsupported rvalue register for aug assign", str(rvalue))  # @todo <<=.word
            if lvalue.register == "A":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tasl  " + Parser.to_hex(Zeropage.SCRATCH_B1))
            elif lvalue.register == "X":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tpha")
                self.p("\t\ttxa")
                self.p("\t\tasl  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                self.p("\t\ttax")
                self.p("\t\tpla")
            elif lvalue.register == "Y":
                self.p("\t\tst{:s}  {:s}".format(rvalue.register.lower(), Parser.to_hex(Zeropage.SCRATCH_B1)))
                self.p("\t\tpha")
                self.p("\t\ttya")
                self.p("\t\tasl  " + Parser.to_hex(Zeropage.SCRATCH_B1))
                self.p("\t\ttay")
                self.p("\t\tpla")
            else:
                raise CodeError("unsupported lvalue register for aug assign", str(lvalue))  # @todo <<=.word

    def generate_assignment(self, stmt: ParseResult.AssignmentStmt) -> None:
        def unwrap_indirect(iv: ParseResult.IndirectValue) -> ParseResult.MemMappedValue:
            if isinstance(iv.value, ParseResult.MemMappedValue):
                return iv.value
            elif iv.value.constant and isinstance(iv.value, ParseResult.IntegerValue):
                return ParseResult.MemMappedValue(iv.value.value, iv.datatype, 1, iv.name)
            else:
                raise CodeError("cannot yet generate code for assignment: non-constant and non-memmapped indirect")  # XXX

        rvalue = stmt.right
        if isinstance(rvalue, ParseResult.IndirectValue):
            rvalue = unwrap_indirect(rvalue)
        self.p("\t\t\t\t\t; src l. {:d}".format(stmt.lineno))
        if isinstance(rvalue, ParseResult.IntegerValue):
            for lv in stmt.leftvalues:
                if isinstance(lv, ParseResult.RegisterValue):
                    self.generate_assign_integer_to_reg(lv.register, rvalue)
                elif isinstance(lv, ParseResult.MemMappedValue):
                    self.generate_assign_integer_to_mem(lv, rvalue)
                elif isinstance(lv, ParseResult.IndirectValue):
                    lv = unwrap_indirect(lv)
                    self.generate_assign_integer_to_mem(lv, rvalue)
                else:
                    raise CodeError("invalid assignment target (1)", str(stmt))
        elif isinstance(rvalue, ParseResult.RegisterValue):
            for lv in stmt.leftvalues:
                if isinstance(lv, ParseResult.RegisterValue):
                    self.generate_assign_reg_to_reg(lv, rvalue.register)
                elif isinstance(lv, ParseResult.MemMappedValue):
                    self.generate_assign_reg_to_memory(lv, rvalue.register)
                elif isinstance(lv, ParseResult.IndirectValue):
                    lv = unwrap_indirect(lv)
                    self.generate_assign_reg_to_memory(lv, rvalue.register)
                else:
                    raise CodeError("invalid assignment target (2)", str(stmt))
        elif isinstance(rvalue, ParseResult.StringValue):
            r_str = self.output_string(rvalue.value, True)
            for lv in stmt.leftvalues:
                if isinstance(lv, ParseResult.RegisterValue):
                    if len(rvalue.value) == 1:
                        self.generate_assign_char_to_reg(lv, r_str)
                    else:
                        self.generate_assign_string_to_reg(lv, rvalue)
                elif isinstance(lv, ParseResult.MemMappedValue):
                    if len(rvalue.value) == 1:
                        self.generate_assign_char_to_memory(lv, r_str)
                    else:
                        self.generate_assign_string_to_memory(lv, rvalue)
                elif isinstance(lv, ParseResult.IndirectValue):
                    lv = unwrap_indirect(lv)
                    if len(rvalue.value) == 1:
                        self.generate_assign_char_to_memory(lv, r_str)
                    else:
                        self.generate_assign_string_to_memory(lv, rvalue)
                else:
                    raise CodeError("invalid assignment target (2)", str(stmt))
        elif isinstance(rvalue, ParseResult.MemMappedValue):
            for lv in stmt.leftvalues:
                if isinstance(lv, ParseResult.RegisterValue):
                    self.generate_assign_mem_to_reg(lv.register, rvalue)
                elif isinstance(lv, ParseResult.MemMappedValue):
                    self.generate_assign_mem_to_mem(lv, rvalue)
                elif isinstance(lv, ParseResult.IndirectValue):
                    lv = unwrap_indirect(lv)
                    self.generate_assign_mem_to_mem(lv, rvalue)
                else:
                    raise CodeError("invalid assignment target (4)", str(stmt))
        elif isinstance(rvalue, ParseResult.FloatValue):
            for lv in stmt.leftvalues:
                if isinstance(lv, ParseResult.MemMappedValue) and lv.datatype == DataType.FLOAT:
                    self.generate_assign_float_to_mem(lv, rvalue)
                elif isinstance(lv, ParseResult.IndirectValue):
                    lv = unwrap_indirect(lv)
                    assert lv.datatype == DataType.FLOAT
                    self.generate_assign_float_to_mem(lv, rvalue)
                else:
                    raise CodeError("cannot assign float to ", str(lv))
        else:
            raise CodeError("invalid assignment value type", str(stmt))

    def generate_assign_float_to_mem(self, mmv: ParseResult.MemMappedValue,
                                     rvalue: Union[ParseResult.FloatValue, ParseResult.IntegerValue], save_reg: bool=True) -> None:
        floatvalue = float(rvalue.value)
        mflpt = self.to_mflpt5(floatvalue)
        target = mmv.name or Parser.to_hex(mmv.address)
        if save_reg:
            self.p("\t\tpha\t\t\t; {:s} = {}".format(target, rvalue.name or floatvalue))
        else:
            self.p("\t\t\t\t\t; {:s} = {}".format(target, rvalue.name or floatvalue))
        for num in range(5):
            self.p("\t\tlda  #${:02x}".format(mflpt[num]))
            self.p("\t\tsta  {:s}+{:d}".format(target, num))
        if save_reg:
            self.p("\t\tpla")

    def generate_assign_reg_to_memory(self, lv: ParseResult.MemMappedValue, r_register: str) -> None:
        # Memory = Register
        lv_string = lv.name or Parser.to_hex(lv.address)
        if lv.datatype == DataType.BYTE:
            if len(r_register) > 1:
                raise CodeError("cannot assign register pair to single byte memory")
            self.p("\t\tst{:s}  {}".format(r_register.lower(), lv_string))
        elif lv.datatype == DataType.WORD:
            if len(r_register) == 1:
                self.p("\t\tst{:s}  {}".format(r_register.lower(), lv_string))  # lsb
                with self.preserving_registers({'A'}, loads_a_within=True):
                    self.p("\t\tlda  #0")
                    self.p("\t\tsta  {:s}+1".format(lv_string))  # msb
            else:
                self.p("\t\tst{:s}  {}".format(r_register[0].lower(), lv_string))
                self.p("\t\tst{:s}  {}+1".format(r_register[1].lower(), lv_string))
        elif lv.datatype == DataType.FLOAT:
            # assigning a register to a float requires c64 ROM routines
            if r_register in REGISTER_WORDS:
                def do_rom_calls():
                    self.p("\t\tjsr  c64util.GIVUAYF")  # uword AY -> fac1
                    self.p("\t\tldx  #<" + lv_string)
                    self.p("\t\tldy  #>" + lv_string)
                    self.p("\t\tjsr  c64.FTOMEMXY")  # fac1 -> memory XY
                if r_register == "AY":
                    with self.preserving_registers({'A', 'X', 'Y'}):
                        do_rom_calls()
                elif r_register == "AX":
                    with self.preserving_registers({'A', 'X', 'Y'}):
                        self.p("\t\tpha\n\t\ttxa\n\t\ttay\n\t\tpla")    # X->Y (so we have AY now)
                        do_rom_calls()
                else:  # XY
                    with self.preserving_registers({'A', 'X', 'Y'}, loads_a_within=True):
                        self.p("\t\ttxa")    # X->A (so we have AY now)
                        do_rom_calls()
            elif r_register in "AXY":

                def do_rom_calls():
                    self.p("\t\tjsr  c64.FREADUY")  # ubyte Y -> fac1
                    self.p("\t\tldx  #<" + lv_string)
                    self.p("\t\tldy  #>" + lv_string)
                    self.p("\t\tjsr  c64.FTOMEMXY")  # fac1 -> memory XY

                if r_register == "A":
                    with self.preserving_registers({'A', 'X', 'Y'}):
                        self.p("\t\ttay")
                        do_rom_calls()
                elif r_register == "X":
                    with self.preserving_registers({'A', 'X', 'Y'}, loads_a_within=True):
                        self.p("\t\ttxa")
                        self.p("\t\ttay")
                        do_rom_calls()
                elif r_register == "Y":
                    with self.preserving_registers({'A', 'X', 'Y'}):
                        do_rom_calls()
            else:
                raise CodeError("invalid register to assign to float", r_register)
        else:
            raise CodeError("invalid lvalue type", lv.datatype)

    def generate_assign_reg_to_reg(self, lv: ParseResult.RegisterValue, r_register: str) -> None:
        if lv.register != r_register:
            if lv.register == 'A':  # x/y -> a
                self.p("\t\tt{:s}a".format(r_register.lower()))
            elif lv.register == 'Y':
                if r_register == 'A':
                    # a -> y
                    self.p("\t\ttay")
                else:
                    # x -> y, 6502 doesn't have txy
                    self.p("\t\tstx  ${0:02x}\n\t\tldy  ${0:02x}".format(Zeropage.SCRATCH_B1))
            elif lv.register == 'X':
                if r_register == 'A':
                    # a -> x
                    self.p("\t\ttax")
                else:
                    # y -> x, 6502 doesn't have tyx
                    self.p("\t\tsty  ${0:02x}\n\t\tldx  ${0:02x}".format(Zeropage.SCRATCH_B1))
            elif lv.register in REGISTER_WORDS:
                if len(r_register) == 1:
                    # assign one register to a pair, so the hi byte is zero.
                    if lv.register == "AX" and r_register == "A":
                        self.p("\t\tldx  #0")
                    elif lv.register == "AX" and r_register == "X":
                        self.p("\t\ttxa\n\t\tldx  #0")
                    elif lv.register == "AX" and r_register == "Y":
                        self.p("\t\ttya\n\t\tldx  #0")
                    elif lv.register == "AY" and r_register == "A":
                        self.p("\t\tldy  #0")
                    elif lv.register == "AY" and r_register == "X":
                        self.p("\t\ttxa\n\t\tldy  #0")
                    elif lv.register == "AY" and r_register == "Y":
                        self.p("\t\ttya\n\t\tldy  #0")
                    elif lv.register == "XY" and r_register == "A":
                        self.p("\t\ttax\n\t\tldy  #0")
                    elif lv.register == "XY" and r_register == "X":
                        self.p("\t\tldy  #0")
                    elif lv.register == "XY" and r_register == "Y":
                        self.p("\t\ttyx\n\t\tldy  #0")
                    else:
                        raise CodeError("invalid register combination", lv.register, r_register)
                elif lv.register == "AX" and r_register == "AY":
                    # y -> x, 6502 doesn't have tyx
                    self.p("\t\tsty  ${0:02x}\n\t\tldx  ${0:02x}".format(Zeropage.SCRATCH_B1))
                elif lv.register == "AX" and r_register == "XY":
                    self.p("\t\ttxa")
                    # y -> x, 6502 doesn't have tyx
                    self.p("\t\tsty  ${0:02x}\n\t\tldx  ${0:02x}".format(Zeropage.SCRATCH_B1))
                elif lv.register == "AY" and r_register == "AX":
                    # x -> y, 6502 doesn't have txy
                    self.p("\t\tstx  ${0:02x}\n\t\tldy  ${0:02x}".format(Zeropage.SCRATCH_B1))
                elif lv.register == "AY" and r_register == "XY":
                    self.p("\t\ttxa")
                elif lv.register == "XY" and r_register == "AX":
                    self.p("\t\ttax")
                    # x -> y, 6502 doesn't have txy
                    self.p("\t\tstx  ${0:02x}\n\t\tldy  ${0:02x}".format(Zeropage.SCRATCH_B1))
                elif lv.register == "XY" and r_register == "AY":
                    self.p("\t\ttax")
                else:
                    raise CodeError("invalid register combination", lv.register, r_register)
            else:
                raise CodeError("invalid register " + lv.register)

    @contextlib.contextmanager
    def preserving_registers(self, registers: Set[str], loads_a_within: bool=False):
        # this clobbers a ZP scratch register and is therefore NOT safe to use in interrupts
        # see http://6502.org/tutorials/register_preservation.html
        if registers == {'A'}:
            self.p("\t\tpha")
            yield
            self.p("\t\tpla")
        elif registers:
            if not loads_a_within:
                self.p("\t\tsta  ${:02x}".format(Zeropage.SCRATCH_B2))
            if 'A' in registers:
                self.p("\t\tpha")
            if 'X' in registers:
                self.p("\t\ttxa\n\t\tpha")
            if 'Y' in registers:
                self.p("\t\ttya\n\t\tpha")
            if not loads_a_within:
                self.p("\t\tlda  ${:02x}".format(Zeropage.SCRATCH_B2))
            yield
            if 'X' in registers and 'Y' in registers:
                if 'A' not in registers:
                    self.p("\t\tsta  ${:02x}".format(Zeropage.SCRATCH_B2))
                    self.p("\t\tpla\n\t\ttay")
                    self.p("\t\tpla\n\t\ttax")
                    self.p("\t\tlda  ${:02x}".format(Zeropage.SCRATCH_B2))
                else:
                    self.p("\t\tpla\n\t\ttay")
                    self.p("\t\tpla\n\t\ttax")
            else:
                if 'Y' in registers:
                    if 'A' not in registers:
                        self.p("\t\tsta  ${:02x}".format(Zeropage.SCRATCH_B2))
                        self.p("\t\tpla\n\t\ttay")
                        self.p("\t\tlda  ${:02x}".format(Zeropage.SCRATCH_B2))
                    else:
                        self.p("\t\tpla\n\t\ttay")
                if 'X' in registers:
                    if 'A' not in registers:
                        self.p("\t\tsta  ${:02x}".format(Zeropage.SCRATCH_B2))
                        self.p("\t\tpla\n\t\ttax")
                        self.p("\t\tlda  ${:02x}".format(Zeropage.SCRATCH_B2))
                    else:
                        self.p("\t\tpla\n\t\ttax")
            if 'A' in registers:
                self.p("\t\tpla")
        else:
            yield

    def generate_assign_integer_to_mem(self, lv: ParseResult.MemMappedValue, rvalue: ParseResult.IntegerValue) -> None:
        if lv.name:
            symblock, sym = self.cur_block.lookup(lv.name)
            if not isinstance(sym, VariableDef):
                raise CodeError("invalid lvalue type " + str(sym))
            assign_target = symblock.label + '.' + sym.name if symblock is not self.cur_block else lv.name
            lvdatatype = sym.type
        else:
            assign_target = Parser.to_hex(lv.address)
            lvdatatype = lv.datatype
        r_str = rvalue.name if rvalue.name else "${:x}".format(rvalue.value)
        if lvdatatype == DataType.BYTE:
            if rvalue.value is not None and not lv.assignable_from(rvalue) or rvalue.datatype != DataType.BYTE:
                raise OverflowError("value doesn't fit in a byte")
            with self.preserving_registers({'A'}, loads_a_within=True):
                self.p("\t\tlda  #" + r_str)
                self.p("\t\tsta  " + assign_target)
        elif lvdatatype == DataType.WORD:
            if rvalue.value is not None and not lv.assignable_from(rvalue):
                raise OverflowError("value doesn't fit in a word")
            with self.preserving_registers({'A'}, loads_a_within=True):
                self.p("\t\tlda  #<" + r_str)
                self.p("\t\tsta  " + assign_target)
                self.p("\t\tlda  #>" + r_str)
                self.p("\t\tsta  {}+1".format(assign_target))
        elif lvdatatype == DataType.FLOAT:
            if rvalue.value is not None and not DataType.FLOAT.assignable_from_value(rvalue.value):
                raise CodeError("value cannot be assigned to a float")
            self.generate_assign_float_to_mem(lv, rvalue, False)
        else:
            raise CodeError("invalid lvalue type " + str(lvdatatype))

    def generate_assign_mem_to_reg(self, l_register: str, rvalue: ParseResult.MemMappedValue) -> None:
        r_str = rvalue.name if rvalue.name else "${:x}".format(rvalue.address)
        if len(l_register) == 1:
            if rvalue.datatype != DataType.BYTE:
                raise CodeError("can only assign a byte to a register")
            self.p("\t\tld{:s}  {:s}".format(l_register.lower(), r_str))
        else:
            if rvalue.datatype == DataType.BYTE:
                self.p("\t\tld{:s}  {:s}".format(l_register[0].lower(), r_str))
                self.p("\t\tld{:s}  #0".format(l_register[1].lower()))
            elif rvalue.datatype == DataType.WORD:
                self.p("\t\tld{:s}  {:s}".format(l_register[0].lower(), r_str))
                self.p("\t\tld{:s}  {:s}+1".format(l_register[1].lower(), r_str))
            else:
                raise CodeError("can only assign a byte or word to a register pair")

    def generate_assign_mem_to_mem(self, lv: ParseResult.MemMappedValue, rvalue: ParseResult.MemMappedValue) -> None:
        r_str = rvalue.name or Parser.to_hex(rvalue.address)
        l_str = lv.name or Parser.to_hex(lv.address)
        if lv.datatype == DataType.BYTE:
            if rvalue.datatype != DataType.BYTE:
                raise CodeError("can only assign a byte to a byte", str(rvalue))
            with self.preserving_registers({'A'}, loads_a_within=True):
                self.p("\t\tlda  " + r_str)
                self.p("\t\tsta  " + l_str)
        elif lv.datatype == DataType.WORD:
            if rvalue.datatype == DataType.BYTE:
                with self.preserving_registers({'A'}, loads_a_within=True):
                    self.p("\t\tlda  " + r_str)
                    self.p("\t\tsta  " + l_str)
                    self.p("\t\tlda  #0")
                    self.p("\t\tsta  {:s}+1".format(l_str))
            elif rvalue.datatype == DataType.WORD:
                with self.preserving_registers({'A'}, loads_a_within=True):
                    self.p("\t\tlda  {:s}".format(r_str))
                    self.p("\t\tsta  {:s}".format(l_str))
                    self.p("\t\tlda  {:s}+1".format(r_str))
                    self.p("\t\tsta  {:s}+1".format(l_str))
            else:
                raise CodeError("can only assign a byte or word to a word", str(rvalue))
        elif lv.datatype == DataType.FLOAT:
            if rvalue.datatype == DataType.FLOAT:
                with self.preserving_registers({'A'}, loads_a_within=True):
                    self.p("\t\tlda  " + r_str)
                    self.p("\t\tsta  " + l_str)
                    self.p("\t\tlda  {:s}+1".format(r_str))
                    self.p("\t\tsta  {:s}+1".format(l_str))
                    self.p("\t\tlda  {:s}+2".format(r_str))
                    self.p("\t\tsta  {:s}+2".format(l_str))
                    self.p("\t\tlda  {:s}+3".format(r_str))
                    self.p("\t\tsta  {:s}+3".format(l_str))
                    self.p("\t\tlda  {:s}+4".format(r_str))
                    self.p("\t\tsta  {:s}+4".format(l_str))
            elif rvalue.datatype == DataType.BYTE:
                with self.preserving_registers({'A', 'X', 'Y'}):
                    self.p("\t\tldy  " + r_str)
                    self.p("\t\tjsr  c64.FREADUY")  # ubyte Y -> fac1
                    self.p("\t\tldx  #<" + l_str)
                    self.p("\t\tldy  #>" + l_str)
                    self.p("\t\tjsr  c64.FTOMEMXY")  # fac1 -> memory XY
            elif rvalue.datatype == DataType.WORD:
                with self.preserving_registers({'A', 'X', 'Y'}, loads_a_within=True):
                    self.p("\t\tlda  " + r_str)
                    self.p("\t\tldy  {:s}+1".format(r_str))
                    self.p("\t\tjsr  c64util.GIVUAYF")  # uword AY -> fac1
                    self.p("\t\tldx  #<" + l_str)
                    self.p("\t\tldy  #>" + l_str)
                    self.p("\t\tjsr  c64.FTOMEMXY")  # fac1 -> memory XY
            else:
                raise CodeError("unsupported rvalue to memfloat", str(rvalue))
        else:
            raise CodeError("invalid lvalue memmapped datatype", str(lv))

    def generate_assign_char_to_memory(self, lv: ParseResult.MemMappedValue, char_str: str) -> None:
        # Memory = Character
        with self.preserving_registers({'A'}, loads_a_within=True):
            self.p("\t\tlda  #" + char_str)
            if not lv.name:
                self.p("\t\tsta  " + Parser.to_hex(lv.address))
                return
            # assign char value to a memory location by symbol name
            symblock, sym = self.cur_block.lookup(lv.name)
            if isinstance(sym, VariableDef):
                assign_target = lv.name
                if symblock is not self.cur_block:
                    assign_target = symblock.label + '.' + sym.name
                if sym.type == DataType.BYTE:
                    self.p("\t\tsta  " + assign_target)
                elif sym.type == DataType.WORD:
                    self.p("\t\tsta  " + assign_target)
                    self.p("\t\tlda  #0")
                    self.p("\t\tsta  {}+1".format(assign_target))
                else:
                    raise CodeError("invalid lvalue type " + str(sym))
            else:
                raise CodeError("invalid lvalue type " + str(sym))

    def generate_assign_integer_to_reg(self, l_register: str, rvalue: ParseResult.IntegerValue) -> None:
        r_str = rvalue.name if rvalue.name else "${:x}".format(rvalue.value)
        if l_register in ('A', 'X', 'Y'):
            self.p("\t\tld{:s}  #{:s}".format(l_register.lower(), r_str))
        elif l_register in REGISTER_WORDS:
            self.p("\t\tld{:s}  #<{:s}".format(l_register[0].lower(), r_str))
            self.p("\t\tld{:s}  #>{:s}".format(l_register[1].lower(), r_str))
        elif l_register == "SC":
            # set/clear S carry bit
            if rvalue.value:
                self.p("\t\tsec")
            else:
                self.p("\t\tclc")
        elif l_register == "SI":
            # interrupt disable bit
            if rvalue.value:
                self.p("\t\tsei")
            else:
                self.p("\t\tcli")
        else:
            raise CodeError("invalid register in immediate integer assignment", l_register, rvalue.value)

    def generate_assign_char_to_reg(self, lv: ParseResult.RegisterValue, char_str: str) -> None:
        # Register = Char (string of length 1)
        if lv.register not in ('A', 'X', 'Y'):
            raise CodeError("invalid register for char assignment", lv.register)
        self.p("\t\tld{:s}  #{:s}".format(lv.register.lower(), char_str))

    def generate_assign_string_to_reg(self, lv: ParseResult.RegisterValue, rvalue: ParseResult.StringValue) -> None:
        if lv.register not in ("AX", "AY", "XY"):
            raise CodeError("need register pair AX, AY or XY for string address assignment", lv.register)
        if rvalue.name:
            self.p("\t\tld{:s}  #<{:s}".format(lv.register[0].lower(), rvalue.name))
            self.p("\t\tld{:s}  #>{:s}".format(lv.register[1].lower(), rvalue.name))
        else:
            raise CodeError("cannot assign immediate string, it should be a string variable")

    def generate_assign_string_to_memory(self, lv: ParseResult.MemMappedValue, rvalue: ParseResult.StringValue) -> None:
        if lv.datatype != DataType.WORD:
            raise CodeError("need word memory type for string address assignment")
        if rvalue.name:
            assign_target = lv.name if lv.name else Parser.to_hex(lv.address)
            self.p("\t\tlda  #<{:s}".format(rvalue.name))
            self.p("\t\tsta  " + assign_target)
            self.p("\t\tlda  #>{:s}".format(rvalue.name))
            self.p("\t\tsta  {}+1".format(assign_target))
        else:
            raise CodeError("cannot assign immediate string, it should be a string variable")

    def footer(self) -> None:
        self.p("\n\n.end")

    def output_string(self, value: str, screencodes: bool = False) -> str:
        if len(value) == 1 and screencodes:
            if value[0].isprintable() and ord(value[0]) < 128:
                return "'{:s}'".format(value[0])
            else:
                return str(ord(value[0]))
        result = '"'
        for char in value:
            if char in "{}":
                result += '", {:d}, "'.format(ord(char))
            elif char.isprintable() and ord(char) < 128:
                result += char
            else:
                if screencodes:
                    result += '", {:d}, "'.format(ord(char))
                else:
                    if char == '\f':
                        result += "{clear}"
                    elif char == '\b':
                        result += "{delete}"
                    elif char == '\n':
                        result += "{cr}"
                    elif char == '\r':
                        result += "{down}"
                    elif char == '\t':
                        result += "{tab}"
                    else:
                        result += '", {:d}, "'.format(ord(char))
        return result + '"'


class Assembler64Tass:
    def __init__(self, format: ProgramFormat) -> None:
        self.format = format

    def assemble(self, inputfilename: str, outputfilename: str) -> None:
        args = ["64tass", "--ascii", "--case-sensitive", "-Wall", "-Wno-strict-bool",
                "--dump-labels", "--vice-labels", "-l", outputfilename+".vice-mon-list",
                "-L", outputfilename+".final-asm", "--no-monitor", "--output", outputfilename, inputfilename]
        if self.format == ProgramFormat.PRG:
            args.append("--cbm-prg")
        elif self.format == ProgramFormat.RAW:
            args.append("--nostart")
        else:
            raise ValueError("don't know how to create format "+str(self.format))
        try:
            if self.format == ProgramFormat.PRG:
                print("\ncreating C-64 prg")
            elif self.format == ProgramFormat.RAW:
                print("\ncreating raw binary")
            try:
                subprocess.check_call(args)
            except FileNotFoundError as x:
                raise SystemExit("ERROR: cannot run assembler program: "+str(x))
        except subprocess.CalledProcessError as x:
            raise SystemExit("assembler failed with returncode " + str(x.returncode))

    def generate_breakpoint_list(self, program_filename: str) -> str:
        breakpoints = []
        with open(program_filename + ".final-asm", "rU") as f:
            for line in f:
                match = re.fullmatch(CodeGenerator.BREAKPOINT_COMMENT_DETECTOR, line, re.DOTALL)
                if match:
                    breakpoints.append("$" + match.group("address"))
        cmdfile = program_filename + ".vice-mon-list"
        with open(cmdfile, "at") as f:
            print("; vice monitor breakpoint list now follows", file=f)
            print("; {:d} breakpoints have been defined here".format(len(breakpoints)), file=f)
            print("del", file=f)
            for b in breakpoints:
                print("break", b, file=f)
        return cmdfile