From e41dd1aa0198e0aeaa495d710937e70b191d605e Mon Sep 17 00:00:00 2001
From: Chris Pressey <cpressey@catseye.tc>
Date: Fri, 24 Nov 2017 13:09:10 +0000
Subject: [PATCH] Attempt to add Zero Page addressing; the emitter may need
 rethink.

---
 README.markdown                 | 11 ++++++++---
 src/sixtypical/compiler.py      | 11 +++++++++--
 src/sixtypical/emitter.py       |  4 ++++
 src/sixtypical/gen6502.py       | 16 +++++++++++++++-
 tests/SixtyPical Compilation.md | 16 ++++++++++++++++
 5 files changed, 52 insertions(+), 6 deletions(-)

diff --git a/README.markdown b/README.markdown
index 60d8a55..b38da83 100644
--- a/README.markdown
+++ b/README.markdown
@@ -49,13 +49,18 @@ A `pointer` is implemented as a zero-page memory location, and accessing the
 buffer pointed to is implemented with "indirect indexed" addressing, as in
 
     LDA ($02), Y
+    STA ($02), Y
 
 We will likely have a new mode of `copy` for this, like
 
-    copy 100, [ptr] + y
+    copy ^buf, ptr           // this is the only way to initialize a pointer
+    add ptr, 4               // ok, but only if it does not exceed buffer's size
+    ld y, 0                  // you must set this to something yourself
+    copy [ptr] + y, byt      // read memory through pointer, into byte
+    copy 100, [ptr] + y      // write memory through pointer (still trashes a)
 
-where `ptr` is a user-defined storage location of `pointer` type, and `+ y`
-is mandatory (and you can/should set it to zero yourself if you want.)
+where `ptr` is a user-defined storage location of `pointer` type, and the
+`+ y` part is mandatory.
 
 This instruction will likely be unchecked, at least to start.  Basically,
 this is to allow us to write to the `byte buffer[2048]` known as "the screen",
diff --git a/src/sixtypical/compiler.py b/src/sixtypical/compiler.py
index 049504e..6f58e90 100644
--- a/src/sixtypical/compiler.py
+++ b/src/sixtypical/compiler.py
@@ -8,7 +8,7 @@ from sixtypical.model import (
 )
 from sixtypical.emitter import Byte, Label, Offset, LowAddressByte, HighAddressByte
 from sixtypical.gen6502 import (
-    Immediate, Absolute, AbsoluteX, AbsoluteY, Indirect, IndirectY, Relative,
+    Immediate, Absolute, AbsoluteX, AbsoluteY, ZeroPage, Indirect, IndirectY, Relative,
     LDA, LDX, LDY, STA, STX, STY,
     TAX, TAY, TXA, TYA,
     CLC, SEC, ADC, SBC, ROL, ROR,
@@ -299,7 +299,14 @@ class Compiler(object):
                     self.emitter.emit(LDA(Absolute(Offset(src_label, 1))))
                     self.emitter.emit(STA(Absolute(Offset(dest_label, 1))))
             elif isinstance(src.type, BufferType) and isinstance(dest.type, PointerType):
-                raise NotImplementedError('zeropage')
+                # TODO: this maybe should not be the 'copy' opcode at all that means this
+                src_label = self.labels[src.name]
+                dest_label = self.labels[dest.name]                
+                self.emitter.emit(LDA(Immediate(HighAddressByte(src_label))))
+                self.emitter.emit(STA(ZeroPage(dest_label)))
+                self.emitter.emit(LDA(Immediate(LowAddressByte(src_label))))
+                #self.emitter.emit(STA(ZeroPage(Offset(dest_label, 1))))
+                self.emitter.emit(STA(ZeroPage(dest_label)))
             elif isinstance(src.type, VectorType) and isinstance(dest.type, VectorType):
                 src_label = self.labels[src.name]
                 dest_label = self.labels[dest.name]
diff --git a/src/sixtypical/emitter.py b/src/sixtypical/emitter.py
index 5ae2225..651d15e 100644
--- a/src/sixtypical/emitter.py
+++ b/src/sixtypical/emitter.py
@@ -61,6 +61,10 @@ class Label(Emittable):
         assert self.addr is not None, "unresolved label: %s" % self.name
         return Byte(self.addr - (addr + 2)).serialize()
 
+    def serialize_as_zero_page(self, offset=0):
+        assert self.addr is not None, "unresolved label: %s" % self.name
+        return Byte(self.addr + offset).serialize()
+
     def __repr__(self):
         addrs = ', addr=%r' % self.addr if self.addr is not None else ''
         return "%s(%r%s)" % (self.__class__.__name__, self.name, addrs)
diff --git a/src/sixtypical/gen6502.py b/src/sixtypical/gen6502.py
index cad4be0..b72471e 100644
--- a/src/sixtypical/gen6502.py
+++ b/src/sixtypical/gen6502.py
@@ -58,6 +58,18 @@ class AbsoluteY(Absolute):
     pass
 
 
+class ZeroPage(AddressingMode):
+    def __init__(self, value):
+        assert isinstance(value, (Label, Offset))
+        self.value = value
+
+    def size(self):
+        return 1
+
+    def serialize(self, addr=None):
+        return self.value.serialize_as_zero_page()
+
+
 class Indirect(AddressingMode):
     def __init__(self, value):
         assert isinstance(value, Label)
@@ -76,7 +88,7 @@ class IndirectY(AddressingMode):
         self.value = value
 
     def size(self):
-        return 2
+        return 1
 
     def serialize(self, addr=None):
         return self.value.serialize()
@@ -257,6 +269,7 @@ class LDA(Instruction):
         AbsoluteX: 0xbd,
         AbsoluteY: 0xb9,
         IndirectY: 0xb1,
+        ZeroPage:  0xa5,
     }
 
 
@@ -334,6 +347,7 @@ class STA(Instruction):
         AbsoluteX: 0x9d,
         AbsoluteY: 0x99,
         IndirectY: 0x91,
+        ZeroPage:  0x85,
     }
 
 
diff --git a/tests/SixtyPical Compilation.md b/tests/SixtyPical Compilation.md
index 2864447..b0e5398 100644
--- a/tests/SixtyPical Compilation.md	
+++ b/tests/SixtyPical Compilation.md	
@@ -341,3 +341,19 @@ goto.
     |     goto bar
     | }
     = 00c0a0c84c06c060a2c860
+
+Buffers and pointers.
+
+    > | buffer[2048] buf
+    > | pointer ptr : 254
+    > | 
+    > | routine main
+    > |   inputs buf
+    > |   outputs buf, y
+    > |   trashes a, z, n, ptr
+    > | {
+    > |     ld y, 0
+    > |     copy buf, ptr
+    > |     // copy 123, [ptr] + y
+    > | }
+    > = 00c0a000a90b850dc0a9c0850ec060