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fixed VRCP instruction to match the real hardware results

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This commit is contained in:
Nicola Salmoria 2008-01-21 21:41:33 +00:00
parent 3924c0bc9c
commit b0e569464a
1 changed files with 42 additions and 15 deletions
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57
src/emu/cpu/rsp/rsp.c
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@ -2301,32 +2301,59 @@ static void handle_vector_ops(UINT32 op)
}
else
{
int negative = 0;
int sign = 0;
int exp = 0;
int mantissa = 0;
if (rec < 0)
{
rec = ~rec+1;
negative = 1;
rec = -rec; // rec = MINUS rec
sign = 1;
}
for (i = 15; i > 0; i--)
// restrict to 10-bit mantissa
for (i = 15; i >= 0; i--)
{
if (rec & (1 << i))
{
rec &= ((0xffc0) >> (15 - i));
i = 0;
exp = i;
mantissa = (rec << (15 - i)) >> 6;
break;
}
}
rec = (INT32)(0x7fffffff / (double)rec);
for (i = 31; i > 0; i--)
if (mantissa == 0x200)
{
if (rec & (1 << i))
{
rec &= ((0xffff8000) >> (31 - i));
i = 0;
}
rec = 0x7fffffff;
}
if (negative)
else
{
rec = ~rec;
rec = 0xffffffffU / mantissa;
//
// simulate rounding error
//
// This has been verified on the real hardware.
//
// I was able to replicate this exact behaviour by using a five-round
// Newton reciprocal method using floorf() on intermediate results
// to force the use of IEEE 754 32bit floats.
// However, for the sake of portability, we'll use integer arithmetic.
//
if (rec & 0x800)
rec += 1;
rec <<= 8;
}
// restrict result to 17 significant bits
rec &= 0x7fffc000;
rec >>= exp;
if (sign)
{
rec = ~rec; // rec = BITWISE NOT rec
}
}