Initial stab at overflow flag implementation in CPU DSL. Probably broken for subtraction

2 files changed, 6 insertions, 5 deletions

diff --git a/cpu_dsl.py b/cpu_dsl.py
index 6401827..e836e08 100755
--- a/cpu_dsl.py
+++ b/cpu_dsl.py
@@ -304,7 +304,7 @@ def _updateFlagsCImpl(prog, params, rawParams):
 		else:
 			lastDst = prog.resolveParam(prog.lastDst, None, {})
 		storage = prog.flags.getStorage(flag)
-		if calc == 'bit' or calc == 'sign' or calc == 'carry' or calc == 'half':
+		if calc == 'bit' or calc == 'sign' or calc == 'carry' or calc == 'half' or calc == 'overflow':
 			myRes = lastDst
 			if calc == 'sign':
 				resultBit = prog.paramSize(prog.lastDst) - 1
@@ -313,6 +313,9 @@ def _updateFlagsCImpl(prog, params, rawParams):
 			elif calc == 'half':
 				resultBit = 4
 				myRes = '({a} ^ {b} ^ {res})'.format(a = prog.lastA, b = prog.lastB, res = lastDst)
+			elif calc == 'overflow':
+				resultBit = prog.paramSize(prog.lastDst) - 1
+				myRes = '((~({a} ^ {b})) & ({a} ^ {res}))'.format(a = prog.lastA, b = prog.lastB, res = lastDst)
 			else:
 				resultBit = int(resultBit)
 			if type(storage) is tuple:
@@ -347,9 +350,7 @@ def _updateFlagsCImpl(prog, params, rawParams):
 				reg = prog.resolveParam(storage, None, {})
 				output.append('\n\t{reg} = {res} == 0;'.format(
 					reg = reg, res = lastDst
-				))			
-		elif calc == 'overflow':
-			pass
+				))
 		elif calc == 'parity':
 			pass
 		else:
diff --git a/ztestrun.c b/ztestrun.c
index 4a59534..42c934f 100644
--- a/ztestrun.c
+++ b/ztestrun.c
@@ -116,7 +116,7 @@ int main(int argc, char ** argv)
 	printf("Flags: SZYHXVNC\n"
 	       "       %d%d%d%d%d%d%d%d\n", 
 			context->last_flag_result >> 7, context->zflag != 0, context->last_flag_result >> 5 & 1, context->chflags >> 3 & 1, 
-			context->last_flag_result >> 3 & 1, context->pvflag != 0, context->nflag, context->chflags >> 7 & 1
+			context->last_flag_result >> 3 & 1, context->pvflag != 0, context->nflag != 0, context->chflags >> 7 & 1
 	);
 	puts("--Alternate Regs--");
 	printf("A: %X\nB: %X\nC: %X\nD: %X\nE: %X\nHL: %X\n",