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Adding the BIT instruction

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This commit is contained in:
Anonymus Raccoon
2020-04-28 23:12:43 +02:00
parent 26ea447f24
commit abe445d202
3 changed files with 79 additions and 5 deletions
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sources/CPU/Instructions/BitsInstructions.cpp
+28
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@@ -27,4 +27,32 @@ namespace ComSquare::CPU
cycles += this->_registers.dl != 0;
return cycles;
}
int CPU::BIT(uint24_t valueAddr, AddressingMode mode)
{
unsigned negativeMask = this->_registers.p.m ? 0x80u : 0x8000u;
unsigned value = this->_bus->read(valueAddr);
if (!this->_registers.p.m)
value += this->_bus->read(valueAddr + 1) << 8u;
if (mode != ImmediateForA) {
this->_registers.p.n = value & negativeMask;
this->_registers.p.v = value & (negativeMask >> 1u);
}
this->_registers.p.z = (value & this->_registers.a) == 0;
int cycles = !this->_registers.p.m;
switch (mode) {
case DirectPage:
case DirectPageIndexedByX:
cycles += this->_registers.dl != 0;
break;
case AbsoluteIndexedByX:
cycles += this->_hasIndexCrossedPageBoundary;
break;
default:
break;
}
return cycles;
}
}