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Fix overflow flag for SBC.

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This commit is contained in:
Radosław Kujawa 2017-02-02 22:54:34 +01:00
parent 1b936f087e
commit a255b093e9
1 changed files with 1 additions and 3 deletions
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4
src/emulation.c
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@ -804,13 +804,11 @@ emul_sbc(rk65c02emu_t *e, void *id, instruction_t *i)
if (!(e->regs.P & P_CARRY))
res--;
if ((e->regs.A ^ res) & (arg ^ res) & 0x80)
if ((e->regs.A ^ res) & ((0xFF-arg) ^ res) & 0x80)
e->regs.P |= P_SIGN_OVERFLOW;
else
e->regs.P &= ~P_SIGN_OVERFLOW;
printf("res is %x\n", res);
/* if the result does not fit into 8 bits then clear carry */
if (res & 0x8000)
e->regs.P &= ~P_CARRY;