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Interpreter: Fix fctiwx rounding

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The interpreter implementation of fctiwx was treating rounding
mode 0 as "round to nearest, ties towards zero", which is not
an actual IEEE-754 rounding mode. The IBM document mentioned
in a comment at the top of the function, on the other hand,
treats rounding mode 0 as "round to nearest, ties to even",
which makes more sense.

This fixes one of JMC's console-recorded F-Zero GX replays on
JitArm64. (JitArm64 uses an interpreter fallback for fctiwx.)
This commit is contained in:
JosJuice 2021-05-22 17:28:04 +02:00
parent 40a4715074
commit 68a5fc55d2
1 changed files with 2 additions and 1 deletions
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Source/Core/Core/PowerPC/Interpreter/Interpreter_FloatingPoint.cpp
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@ -73,7 +73,8 @@ void ConvertToInteger(UGeckoInstruction inst, RoundingMode rounding_mode)
const double t = b + 0.5; const double t = b + 0.5;
i = static_cast<s32>(t); i = static_cast<s32>(t);
if (t - i < 0 || (t - i == 0 && b > 0)) // Ties to even
if (t - i < 0 || (t - i == 0 && (i & 1)))
{ {
i--; i--;
} }