public static byte doArithmeticByte(CpuContext ctx, byte a1, byte a2, bool withCarry, bool isSub)
{
ushort res; /* To detect carry */
if (isSub)
{
ctx.SETFLAG(Z80Flags.F_N);
ctx.VALFLAG(Z80Flags.F_H, (((a1 & 0x0F) - (a2 & 0x0F)) & 0x10) != 0);
res = (ushort)(a1 - a2);
if (withCarry && ctx.GETFLAG(Z80Flags.F_C)) res--;
}
else
{
ctx.RESFLAG(Z80Flags.F_N);
ctx.VALFLAG(Z80Flags.F_H, (((a1 & 0x0F) + (a2 & 0x0F)) & 0x10) != 0);
res = (ushort)(a1 + a2);
if (withCarry && ctx.GETFLAG(Z80Flags.F_C)) res++;
}
ctx.VALFLAG(Z80Flags.F_S, ((res & 0x80) != 0));
ctx.VALFLAG(Z80Flags.F_C, ((res & 0x100) != 0));
ctx.VALFLAG(Z80Flags.F_Z, ((res & 0xff) == 0));
int minuend_sign = a1 & 0x80;
int subtrahend_sign = a2 & 0x80;
int result_sign = res & 0x80;
bool overflow;
if (isSub)
{
overflow = minuend_sign != subtrahend_sign && result_sign != minuend_sign;
}
else
{
overflow = minuend_sign == subtrahend_sign && result_sign != minuend_sign;
}
ctx.VALFLAG(Z80Flags.F_PV, overflow);
adjustFlags(ctx, (byte)res);
return (byte)(res & 0xFF);
}
public static ushort doArithmeticWord(CpuContext ctx, ushort a1, ushort a2, bool withCarry, bool isSub)
{
if (withCarry && ctx.GETFLAG(Z80Flags.F_C))
a2++;
int sum = a1;
if (isSub)
{
sum -= a2;
ctx.VALFLAG(Z80Flags.F_H, (((a1 & 0x0fff) - (a2 & 0x0fff)) & 0x1000) != 0);
}
else
{
sum += a2;
ctx.VALFLAG(Z80Flags.F_H, (((a1 & 0x0fff) + (a2 & 0x0fff)) & 0x1000) != 0);
}
ctx.VALFLAG(Z80Flags.F_C, (sum & 0x10000) != 0);
if (withCarry || isSub)
{
int minuend_sign = a1 & 0x8000;
int subtrahend_sign = a2 & 0x8000;
int result_sign = sum & 0x8000;
bool overflow;
if (isSub)
{
overflow = minuend_sign != subtrahend_sign && result_sign != minuend_sign;
}
else
{
overflow = minuend_sign == subtrahend_sign && result_sign != minuend_sign;
}
ctx.VALFLAG(Z80Flags.F_PV, overflow);
ctx.VALFLAG(Z80Flags.F_S, (sum & 0x8000) != 0);
ctx.VALFLAG(Z80Flags.F_Z, sum == 0);
}
ctx.VALFLAG(Z80Flags.F_N, isSub);
adjustFlags(ctx, (byte)(sum >> 8));
return (ushort)sum;
}
public static byte doRRC(CpuContext ctx, bool adjFlags, byte val)
{
ctx.VALFLAG(Z80Flags.F_C, (val & 0x01) != 0);
val >>= 1;
val |= (byte)((ctx.GETFLAG(Z80Flags.F_C) ? 1 :0) << 7);
adjustFlags(ctx, val);
ctx.RESFLAG(Z80Flags.F_H | Z80Flags.F_N);
if (adjFlags)
adjustFlagSZP(ctx, val);
return val;
}
public static byte doRL(CpuContext ctx, bool adjFlags, byte val)
{
int CY = ctx.GETFLAG(Z80Flags.F_C) ? 1 :0;
ctx.VALFLAG(Z80Flags.F_C, (val & 0x80) != 0);
val <<= 1;
val |= (byte)CY;
adjustFlags(ctx, val);
ctx.RESFLAG(Z80Flags.F_H | Z80Flags.F_N);
if (adjFlags)
adjustFlagSZP(ctx, val);
return val;
}
// The DAA opcode
// According to the value in A and the flags set, add a value to A
// This algorithm taken from:
// http://www.worldofspectrum.org/faq/reference/z80reference.htm
// and verified against the specification in the Zilog
// Z80 Family CPU User Manual, rev. 04, Dec. 2004, pp. 166-167
public static void doDAA(CpuContext ctx)
{
int correction_factor = 0x00;
int carry = 0;
if (ctx.A > 0x99 || ctx.GETFLAG(Z80Flags.F_C))
{
correction_factor |= 0x60;
carry = 1;
}
if ((ctx.A & 0x0f) > 9 || ctx.GETFLAG(Z80Flags.F_H))
correction_factor |= 0x06;
int a_before = ctx.A;
if (ctx.GETFLAG(Z80Flags.F_N))
{
ctx.A = (byte)(ctx.A - correction_factor);
}
else
{
ctx.A = (byte)(ctx.A + correction_factor);
}
ctx.VALFLAG(Z80Flags.F_H, ((a_before ^ ctx.A) & 0x10) != 0);
ctx.VALFLAG(Z80Flags.F_C, carry != 0);
ctx.VALFLAG(Z80Flags.F_S, (ctx.A & 0x80) != 0);
ctx.VALFLAG(Z80Flags.F_Z, (ctx.A == 0));
ctx.VALFLAG(Z80Flags.F_PV, parityBit[ctx.A]);
adjustFlags(ctx, ctx.A);
}
public static void doCCF(CpuContext ctx)
{
ctx.VALFLAG(Z80Flags.F_C, (1 - (ctx.GETFLAG(Z80Flags.F_C) ? 1 : 0) != 0));
ctx.RESFLAG(Z80Flags.F_N);
adjustFlags(ctx, ctx.A);
}
public static void doBIT(CpuContext ctx, int Bit, byte Value)
{
if ((Value & (1 << Bit)) != 0)
{
ctx.RESFLAG(Z80Flags.F_Z | Z80Flags.F_PV);
}
else
{
ctx.SETFLAG(Z80Flags.F_Z | Z80Flags.F_PV);
}
ctx.SETFLAG(Z80Flags.F_H);
ctx.RESFLAG(Z80Flags.F_N);
ctx.RESFLAG(Z80Flags.F_S);
if ((Bit == 7) && !ctx.GETFLAG(Z80Flags.F_Z))
{
ctx.SETFLAG(Z80Flags.F_S);
}
}