Support branching and looping on the n flag.

HISTORY.md

@@ -9,10 +9,11 @@ History of SixtyPical
 *   Added `nop` opcode, which compiles to `NOP` (mainly for timing.)
 *   Accessing zero-page with `ld` and `st` generates zero-page opcodes.
 *   A `byte` or `word` table can be initialized with a list of constants.
+*   Branching and repeating on the `n` flag is now supported.
 *   Specifying multiple SixtyPical source files will produce a single
     compiled result from their combination.
 *   Rudimentary support for Atari 2600 prelude in a 4K cartridge image,
-    and start of an example program in `eg/atari2600` directory.
+    and an example program in `eg/atari2600` directory.
 
 0.14
 ----

eg/atari2600/smiley.60p

@@ -81,7 +81,7 @@ define display_frame routine
     repeat {
         st a, WSYNC
         dec x
-    } until z        // FIXME orig loop used "bpl _wsync_loop"
+    } until n
     st a, WSYNC
 
     //;

src/sixtypical/compiler.py

@@ -15,7 +15,7 @@ from sixtypical.gen6502 import (
     CLC, SEC, ADC, SBC, ROL, ROR,
     INC, INX, INY, DEC, DEX, DEY,
     CMP, CPX, CPY, AND, ORA, EOR,
-    BCC, BCS, BNE, BEQ,
+    BCC, BCS, BNE, BEQ, BPL, BMI,
     JMP, JSR, RTS,
     SEI, CLI,
     NOP,
@@ -518,10 +518,12 @@ class Compiler(object):
             False: {
                 'c': BCC,
                 'z': BNE,
+                'n': BPL,
             },
             True: {
                 'c': BCS,
                 'z': BEQ,
+                'n': BMI,
             },
         }[instr.inverted].get(instr.src.name)
         if cls is None:
@@ -548,10 +550,12 @@ class Compiler(object):
                 False: {
                     'c': BCC,
                     'z': BNE,
+                    'n': BPL,
                 },
                 True: {
                     'c': BCS,
                     'z': BEQ,
+                    'n': BMI,
                 },
             }[instr.inverted].get(instr.src.name)
             if cls is None:

src/sixtypical/gen6502.py

@@ -160,6 +160,18 @@ class BNE(Instruction):
     }
 
 
+class BPL(Instruction):
+    opcodes = {
+        Relative:  0x10,
+    }
+
+
+class BMI(Instruction):
+    opcodes = {
+        Relative:  0x30,
+    }
+
+
 class CLC(Instruction):
     opcodes = {
         Implied:   0x18

tests/SixtyPical Compilation.md

@@ -417,13 +417,13 @@ Compiling `repeat ... until not n`.
     | routine main
     |   trashes a, y, z, n, c
     | {
-    |     ld y, 65
+    |     ld y, 199
     |     repeat {
     |         ld a, y
     |         inc y
     |     } until not n
     | }
-    = $080D   LDY #$41
+    = $080D   LDY #$C7
     = $080F   TYA
     = $0810   INY
     = $0811   BMI $080F