change SBC to be ADC with one's complement instead of two's

It seems that is what was expected when run with nestest.

1 files changed, 5 insertions, 3 deletions

diff --git a/cpu.c b/cpu.c
index c7d25ef..bcaa00b 100644
--- a/cpu.c
+++ b/cpu.c
@@ -664,7 +664,7 @@ static void
 sbc(uint8_t arg)
 {
 	/* SBC is described online as ADC with argument as two's complement */
-	adc(~arg + 1);
+	adc(~arg);
 }
 
 static void
@@ -733,7 +733,8 @@ tay(void)
 static void
 tsx(void)
 {
-	regs.x = PULL();
+//	regs.x = PULL();
+	regs.x = regs.sp;
 
 	STATUS_UPDATE_ZERO(regs.x);
 	STATUS_UPDATE_NEGATIVE(regs.x);
@@ -751,7 +752,8 @@ txa(void)
 static void
 txs(void)
 {
-	PUSH(regs.x);
+//	PUSH(regs.x);
+	regs.sp = regs.x;
 }
 
 static void