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GTE: Use intrinsic CountLeadingZeros()

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Super tiny micro-optimization.
This commit is contained in:
Connor McLaughlin 2020-04-26 18:33:35 +10:00
parent 28a022547f
commit d1e841f55d
1 changed files with 7 additions and 33 deletions
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40
src/core/gte.cpp
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@ -1,41 +1,15 @@
#include "gte.h" #include "gte.h"
#include "common/bitutils.h"
#include <algorithm> #include <algorithm>
#include <array> #include <array>
// TODO: Optimize, intrinsics? ALWAYS_INLINE u32 CountLeadingBits(u32 value)
static inline constexpr u32 CountLeadingZeros(u16 value)
{ {
u32 count = 0; // if top-most bit is set, we want to count ones not zeros
for (u32 i = 0; i < 16 && (value & UINT16_C(0x8000)) == 0; i++) if (value & UINT32_C(0x80000000))
{ value ^= UINT32_C(0xFFFFFFFF);
count++;
value <<= 1;
}
return count; return (value == 0u) ? 32 : CountLeadingZeros(value);
}
static inline constexpr u32 CountLeadingBits(u32 value)
{
u32 count = 0;
if ((value & UINT32_C(0x80000000)) != 0)
{
for (u32 i = 0; i < 32 && ((value & UINT32_C(0x80000000)) != 0); i++)
{
count++;
value <<= 1;
}
}
else
{
for (u32 i = 0; i < 32 && (value & UINT32_C(0x80000000)) == 0; i++)
{
count++;
value <<= 1;
}
}
return count;
} }
namespace GTE { namespace GTE {
@ -365,7 +339,7 @@ u32 Core::UNRDivide(u32 lhs, u32 rhs)
return 0x1FFFF; return 0x1FFFF;
} }
const u32 shift = CountLeadingZeros(static_cast<u16>(rhs)); const u32 shift = (rhs == 0) ? 16 : CountLeadingZeros(static_cast<u16>(rhs));
lhs <<= shift; lhs <<= shift;
rhs <<= shift; rhs <<= shift;