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Implement correct "round to nearest" mode

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On PowerPC round to nearest ties to even, not away from zero
Also implement correct behavior for ppc_fresx
Fixes "tips to win" sequence in Daytona 2 BOTE
This commit is contained in:
gm-matthew 2023-10-15 00:54:59 +01:00 committed by Bart Trzynadlowski
parent d32641030d
commit 392900fee2
1 changed files with 34 additions and 6 deletions
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40
Src/CPU/PowerPC/ppc_ops.c
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@ -33,6 +33,7 @@
// it really seems like this should be elsewhere - like maybe the floating point checks can hang out someplace else
#include <math.h>
#include <cfenv>
static void ppc_unimplemented(UINT32 op)
{
@ -1661,8 +1662,23 @@ inline int sign_double(FPR x)
return ((x.id & DOUBLE_SIGN) != 0);
}
inline void set_rounding_mode(void)
{
// may require compiler option to work correctly (-frounding-math for GCC, /fp:strict for Visual Studio)
// unknown if any games actually change this
switch (ppc.fpscr & 3)
{
case 0: fesetround(FE_TONEAREST); break;
case 1: fesetround(FE_TOWARDZERO); break;
case 2: fesetround(FE_UPWARD); break;
case 3: fesetround(FE_DOWNWARD); break;
}
}
/*
inline INT64 smround_to_nearest(FPR f)
{
// This method is incorrect; it ties away from zero, while PowerPC ties to even
if (f.fd >= 0)
{
return (INT64)(f.fd + 0.5);
@ -1689,6 +1705,7 @@ inline INT64 round_toward_negative_infinity(FPR f)
double r = floor(f.fd);
return (INT64)(r);
}
*/
#define SET_VXSNAN(a, b) if (is_snan_double(a) || is_snan_double(b)) ppc.fpscr |= 0x80000000
#define SET_VXSNAN_1(c) if (is_snan_double(c)) ppc.fpscr |= 0x80000000
@ -2174,10 +2191,12 @@ static void ppc_fctiwx(UINT32 op)
switch(ppc.fpscr & 3)
{
case 0: r = (INT64)smround_to_nearest(FPR(b)); break;
case 1: r = (INT64)smround_toward_zero(FPR(b)); break;
case 2: r = (INT64)round_toward_positive_infinity(FPR(b)); break;
case 3: r = (INT64)round_toward_negative_infinity(FPR(b)); break;
// nearbyint() uses rounding mode set by fesetround()
// this should be FE_TONEAREST (ties to even) if the case is 0
case 0: r = (INT64)nearbyint(FPR(b).fd); break;
case 1: r = (INT64)trunc(FPR(b).fd); break;
case 2: r = (INT64)ceil(FPR(b).fd); break;
case 3: r = (INT64)floor(FPR(b).fd); break;
}
if(r > (INT64)((INT32)0x7FFFFFFF))
@ -2219,7 +2238,7 @@ static void ppc_fctiwzx(UINT32 op)
CHECK_FPU_AVAILABLE();
SET_VXSNAN_1(FPR(b));
r = smround_toward_zero(FPR(b));
r = (INT64)trunc(FPR(b).fd);
if(r > (INT64)((INT32)0x7fffffff))
{
@ -2398,6 +2417,8 @@ static void ppc_mtfsb0x(UINT32 op)
if (crbD != 1 && crbD != 2) // these bits cannot be explicitly cleared
ppc.fpscr &= ~(1 << (31 - crbD));
set_rounding_mode();
if( RCBIT ) {
SET_CR1();
}
@ -2412,6 +2433,8 @@ static void ppc_mtfsb1x(UINT32 op)
if (crbD != 1 && crbD != 2) // these bits cannot be explicitly cleared
ppc.fpscr |= (1 << (31 - crbD));
set_rounding_mode();
if( RCBIT ) {
SET_CR1();
}
@ -2425,6 +2448,8 @@ static void ppc_mtfsfx(UINT32 op)
ppc.fpscr &= (~f) | ~(FPSCR_FEX | FPSCR_VX);
ppc.fpscr |= (UINT32)(FPR(b).id) & ~(FPSCR_FEX | FPSCR_VX);
set_rounding_mode();
// FEX, VX
if( RCBIT ) {
@ -2459,6 +2484,8 @@ static void ppc_mtfsfix(UINT32 op)
ppc.fpscr &= ~(0xf << crfd); // clear field
ppc.fpscr |= (imm << crfd); // insert new data
set_rounding_mode();
if( RCBIT ) {
SET_CR1();
}
@ -2541,7 +2568,8 @@ static void ppc_fresx(UINT32 op)
SET_VXSNAN_1(FPR(b));
FPR(t).fd = 1.0 / FPR(b).fd; /* ??? */
// On the 603 fres behaves the same as fdivs RT, 1.0, RB
FPR(t).fd = (float)(1.0 / FPR(b).fd);
set_fprf(FPR(t));
if( RCBIT ) {