private static Mos6502State Asl(int address, Mos6502State currentState, MemoryUnit memory)
{
var operand = address == 0 ? currentState.A : memory.ReadByte(address);
var r = operand << 1;
var flags = currentState.P;
flags = flags.SetIf(r > 0xFF, Mos6502Flags.Carry);
r = (byte)r;
// Set Zero flag **only** if the accumulator changes to zero.
if (address == 0)
{
flags = flags.SetIf(r == 0, Mos6502Flags.Zero);
}
flags = flags.SetIf((r & 0b1000_0000) != 0, Mos6502Flags.Negative);
if (address == 0)
{
return(currentState.With(a: (byte)r, p: flags));
}
else
{
memory.WriteByte(address, (byte)r);
return(currentState.With(p: flags));
}
}
private static Mos6502State Ahx(int address, Mos6502State currentState, MemoryUnit memory)
{
// AHX is an unofficial opcode with odd behavior
// Based this test on https://github.com/anurse/remy/blob/4f01c0e16ac9b8db1553d97588c9d8927884cef1/src/hw/mos6502/exec/store.rs#L158
// I don't remember where I figured that behavior out then :(.
var highByte = (address & 0xFF00) >> 8;
var val = currentState.A & currentState.X & highByte;
memory.WriteByte(address, (byte)val);
return(currentState);
}
