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Dyncom/VFP: Perform flush-to-zero on the second operand of vsub before sending it to vadd.

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Previously we were letting vadd flush the value to positive 0, but there are cases where this behavior is wrong, for example,

vsub: -0 - +0 = -0
vadd: -0 + +0 = +0

Now we'll flush the value to +0 inside vsub, and then negate it.
This commit is contained in:
Subv 2017-05-08 16:24:08 -05:00
parent e33558c6ce
commit a0874a7a68
1 changed files with 12 additions and 2 deletions
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14
src/core/arm/skyeye_common/vfp/vfpsingle.cpp
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@ -1062,12 +1062,22 @@ static u32 vfp_single_fadd(ARMul_State* state, int sd, int sn, s32 m, u32 fpscr)
static u32 vfp_single_fsub(ARMul_State* state, int sd, int sn, s32 m, u32 fpscr) {
LOG_TRACE(Core_ARM11, "s%u = %08x", sn, sd);
/*
* Subtraction is addition with one sign inverted.
* Subtraction is addition with one sign inverted. Unpack the second operand to perform FTZ if
* necessary, we can't let fadd do this because a denormal in m might get flushed to +0 in FTZ
* mode, and the resulting sign of 0 OP +0 differs between fadd and fsub. We do not need to do
* this for n because +0 OP 0 is always +0 for both fadd and fsub.
*/
struct vfp_single vsm;
u32 exceptions = vfp_single_unpack(&vsm, m, fpscr);
if (exceptions & FPSCR_IDC) {
// The value was flushed to zero, re-pack it.
m = vfp_single_pack(&vsm);
}
if (m != 0x7FC00000) // Only negate if m isn't NaN.
m = vfp_single_packed_negate(m);
return vfp_single_fadd(state, sd, sn, m, fpscr);
return vfp_single_fadd(state, sd, sn, m, fpscr) | exceptions;
}
/*