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RSBinToGroups() use __builtin_clz() instead of manual bsr if available

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should be faster.
This commit is contained in:
Daniel Gibson 2016-04-22 19:40:09 +02:00
parent 46353ffc5d
commit c58328d881
1 changed files with 21 additions and 12 deletions
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33
Sources/Engine/Graphics/DrawPort_RenderScene.cpp
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@ -499,18 +499,27 @@ static void RSBinToGroups( ScenePolygon *pspoFirst)
);
#else
// emulate x86's bsr opcode...not fast. :/
register DWORD val = _ctGroupsCount;
register INDEX bsr = 31;
if (val != 0)
{
while (bsr > 0)
{
if (val & (1l << bsr))
break;
bsr--;
}
}
// emulate x86's bsr opcode...
// GCC and clang have an architecture-independent intrinsic for this
// (it counts leading zeros starting at MSB and is undefined for 0)
#ifdef __GNUC__
INDEX bsr = 31;
if(_ctGroupsCount != 0) bsr -= __builtin_clz(_ctGroupsCount);
else bsr = 0;
#else // another compiler - doing it manually.. not fast. :/
register DWORD val = _ctGroupsCount;
register INDEX bsr = 31;
if (val != 0)
{
while (bsr > 0)
{
if (val & (1l << bsr))
break;
bsr--;
}
}
#endif
_ctGroupsCount = 2 << bsr;
#endif