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CPU: Implement sub instruction

This commit is contained in:
Connor McLaughlin 2019-09-14 13:39:36 +10:00
parent 1afa02d475
commit ced3038e73
1 changed files with 20 additions and 0 deletions
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20
src/pse/cpu_core.cpp
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@ -206,6 +206,11 @@ static constexpr bool AddOverflow(u32 old_value, u32 add_value, u32 new_value)
return (((new_value ^ old_value) & (new_value ^ add_value)) & UINT32_C(0x80000000)) != 0;
}
static constexpr bool SubOverflow(u32 old_value, u32 sub_value, u32 new_value)
{
return (((new_value ^ old_value) & (old_value ^ sub_value)) & UINT32_C(0x80000000)) != 0;
}
void Core::DisassembleAndPrint(u32 addr)
{
u32 bits;
@ -358,6 +363,21 @@ void Core::ExecuteInstruction(Instruction inst, u32 inst_pc)
}
break;
case InstructionFunct::sub:
{
const u32 old_value = ReadReg(inst.r.rs);
const u32 sub_value = ReadReg(inst.r.rt);
const u32 new_value = old_value - sub_value;
if (SubOverflow(old_value, sub_value, new_value))
{
RaiseException(inst_pc, Exception::Ov);
return;
}
WriteReg(inst.r.rd, new_value);
}
break;
case InstructionFunct::subu:
{
const u32 new_value = ReadReg(inst.r.rs) - ReadReg(inst.r.rt);