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Change carry flag strategy according to docs
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5f93bdae25
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@ -32,7 +32,14 @@ DEFINE_INST(adc)
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*/
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DEFINE_INST(cmp)
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{
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mos6502_modify_status(cpu, MOS_NZC, cpu->A, cpu->A - oper);
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mos6502_modify_status(cpu, MOS_NZ, cpu->A, cpu->A - oper);
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// Carry works slightly different with the cmp-style instructions;
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// it's set if A >= oper.
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cpu->P &= ~MOS_CARRY;
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if (cpu->A >= oper) {
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cpu->P |= MOS_CARRY;
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}
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}
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/*
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@ -41,7 +48,12 @@ DEFINE_INST(cmp)
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*/
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DEFINE_INST(cpx)
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{
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mos6502_modify_status(cpu, MOS_NZC, cpu->X, cpu->X - oper);
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mos6502_modify_status(cpu, MOS_NZ, cpu->X, cpu->X - oper);
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cpu->P &= ~MOS_CARRY;
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if (cpu->X >= oper) {
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cpu->P |= MOS_CARRY;
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}
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}
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/*
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@ -50,7 +62,12 @@ DEFINE_INST(cpx)
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*/
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DEFINE_INST(cpy)
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{
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mos6502_modify_status(cpu, MOS_NZC, cpu->Y, cpu->Y - oper);
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mos6502_modify_status(cpu, MOS_NZ, cpu->Y, cpu->Y - oper);
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cpu->P &= ~MOS_CARRY;
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if (cpu->Y >= oper) {
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cpu->P |= MOS_CARRY;
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}
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}
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/*
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