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Set carry if the right-most bit is 1

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Don't consider the left-most bit
This commit is contained in:
Peter Evans 2018-01-21 16:17:31 -06:00
parent 5d8403aaa7
commit 3206332a7d
1 changed files with 11 additions and 2 deletions
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13
src/mos6502.bits.c
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@ -97,8 +97,17 @@ DEFINE_INST(lsr)
{
SET_RESULT(oper >> 1);
// MOS_NEGATIVE is intentionally not included here.
mos6502_modify_status(cpu, MOS_ZC, oper, result);
// Set ZERO if it should apply
mos6502_modify_status(cpu, MOS_ZERO, oper, result);
// However, we handle carry a bit differently here. The carry bit
// should be 1 if oper & 0x1; that is, when we shift right, we want
// the right-most bit to be captured in carry, in just the same way
// we want the left-most bit to be captured in carry for ASL.
cpu->P &= ~MOS_CARRY;
if (oper & 0x1) {
cpu->P |= MOS_CARRY;
}
if (cpu->eff_addr) {
mos6502_set(cpu, cpu->eff_addr, result & 0xff);