Subtract word (constant or memory location) from word memory location.

HISTORY.md

@@ -9,6 +9,7 @@ History of SixtyPical
     in a `copy` to a vector is a routine that is defined further down in the source.
 *   Initialized `word` memory locations.
 *   Can `copy` a literal word to a word table.
+*   Subtract word (constant or memory location) from word memory location.
 *   Fixed bug which was preventing `if` branches to diverge in what they initialized,
     if it was already initialized when going into the `if`.
 *   Fixed a bug which was making it crash when trying to analyze `repeat forever` loops.

src/sixtypical/analyzer.py

@@ -273,9 +273,15 @@ class Analyzer(object):
                 else:
                     self.assert_type(TYPE_WORD, dest)
         elif opcode == 'sub':
-            self.assert_type(TYPE_BYTE, src, dest)
             context.assert_meaningful(src, dest, FLAG_C)
-            context.set_written(dest, FLAG_Z, FLAG_N, FLAG_C, FLAG_V)
+            if src.type == TYPE_BYTE:
+                self.assert_type(TYPE_BYTE, src, dest)
+                context.set_written(dest, FLAG_Z, FLAG_N, FLAG_C, FLAG_V)
+            else:
+                self.assert_type(TYPE_WORD, src, dest)
+                context.set_written(dest, FLAG_Z, FLAG_N, FLAG_C, FLAG_V)
+                context.set_touched(REG_A)
+                context.set_unmeaningful(REG_A)
         elif opcode in ('inc', 'dec'):
             self.assert_type(TYPE_BYTE, dest)
             context.assert_meaningful(dest)

src/sixtypical/compiler.py

@@ -230,6 +230,26 @@ class Compiler(object):
                     self.emitter.emit(SBC(Immediate(Byte(src.value))))
                 else:
                     self.emitter.emit(SBC(Absolute(self.labels[src.name])))
+            elif isinstance(dest, LocationRef) and src.type == TYPE_WORD and dest.type == TYPE_WORD:
+                if isinstance(src, ConstantRef):
+                    dest_label = self.labels[dest.name]
+                    self.emitter.emit(LDA(Absolute(dest_label)))
+                    self.emitter.emit(SBC(Immediate(Byte(src.low_byte()))))
+                    self.emitter.emit(STA(Absolute(dest_label)))
+                    self.emitter.emit(LDA(Absolute(Offset(dest_label, 1))))
+                    self.emitter.emit(SBC(Immediate(Byte(src.high_byte()))))
+                    self.emitter.emit(STA(Absolute(Offset(dest_label, 1))))
+                elif isinstance(src, LocationRef):
+                    src_label = self.labels[src.name]
+                    dest_label = self.labels[dest.name]
+                    self.emitter.emit(LDA(Absolute(dest_label)))
+                    self.emitter.emit(SBC(Absolute(src_label)))
+                    self.emitter.emit(STA(Absolute(dest_label)))
+                    self.emitter.emit(LDA(Absolute(Offset(dest_label, 1))))
+                    self.emitter.emit(SBC(Absolute(Offset(src_label, 1))))
+                    self.emitter.emit(STA(Absolute(Offset(dest_label, 1))))
+                else:
+                    raise UnsupportedOpcodeError(instr)
             else:
                 raise UnsupportedOpcodeError(instr)
         elif opcode == 'inc':

tests/SixtyPical Analysis.md

@@ -593,6 +593,60 @@ Can't `sub` to a memory location that isn't writeable.
     | }
     ? ForbiddenWriteError: a in main
 
+You can `sub` a word constant from a word memory location.
+
+    | word score
+    | routine main
+    |   inputs a, score
+    |   outputs score
+    |   trashes a, c, z, v, n
+    | {
+    |     st on, c
+    |     sub score, 1999
+    | }
+    = ok
+
+`sub`ing a word constant from a word memory location trashes `a`.
+
+    | word score
+    | routine main
+    |   inputs a, score
+    |   outputs score, a
+    |   trashes c, z, v, n
+    | {
+    |     st on, c
+    |     sub score, 1999
+    | }
+    ? UnmeaningfulOutputError: a in main
+
+You can `sub` a word memory location from another word memory location.
+
+    | word score
+    | word delta
+    | routine main
+    |   inputs score, delta
+    |   outputs score
+    |   trashes a, c, z, v, n
+    | {
+    |     st off, c
+    |     sub score, delta
+    | }
+    = ok
+
+`sub`ing a word memory location from a word memory location trashes `a`.
+
+    | word score
+    | word delta
+    | routine main
+    |   inputs score, delta
+    |   outputs score
+    |   trashes c, z, v, n
+    | {
+    |     st off, c
+    |     sub score, delta
+    | }
+    ? ForbiddenWriteError: a in main
+
 ### inc ###
 
 Location must be initialized and writeable.

tests/SixtyPical Compilation.md

@@ -895,6 +895,47 @@ Adding a word memory location to another word memory location.
     = $081D   STA $0822
     = $0820   RTS
 
+Subtracting a constant word from a word memory location.
+
+    | word score
+    | routine main
+    |   inputs score
+    |   outputs score
+    |   trashes a, c, z, v, n
+    | {
+    |     st on, c
+    |     sub score, 1999
+    | }
+    = $080D   SEC
+    = $080E   LDA $081F
+    = $0811   SBC #$CF
+    = $0813   STA $081F
+    = $0816   LDA $0820
+    = $0819   SBC #$07
+    = $081B   STA $0820
+    = $081E   RTS
+
+Subtracting a word memory location from another word memory location.
+
+    | word score
+    | word delta
+    | routine main
+    |   inputs score, delta
+    |   outputs score
+    |   trashes a, c, z, v, n
+    | {
+    |     st on, c
+    |     sub score, delta
+    | }
+    = $080D   SEC
+    = $080E   LDA $0821
+    = $0811   SBC $0823
+    = $0814   STA $0821
+    = $0817   LDA $0822
+    = $081A   SBC $0824
+    = $081D   STA $0822
+    = $0820   RTS
+
 ### Buffers and Pointers
 
 Load address into pointer.