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math: Use MSVC _BitScan intrinsics in countLeadingZeros/countTrailingZeros runtime fast path. (#385)

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This commit is contained in:
Branimir Karadžić
2026-04-24 23:18:15 -07:00
committed by GitHub
parent 8d98acc6f7
commit 0f575d5880
1 changed files with 56 additions and 0 deletions
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56
include/bx/inline/math.inl
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@@ -12,6 +12,22 @@
#include <bx/simd_t.h>
#include <bx/uint32_t.h>
#if BX_COMPILER_MSVC
extern "C" unsigned char _BitScanReverse(unsigned long* _Index, unsigned long _Mask);
# pragma intrinsic(_BitScanReverse)
extern "C" unsigned char _BitScanForward(unsigned long* _Index, unsigned long _Mask);
# pragma intrinsic(_BitScanForward)
# if BX_ARCH_64BIT
extern "C" unsigned char _BitScanReverse64(unsigned long* _Index, unsigned __int64 _Mask);
# pragma intrinsic(_BitScanReverse64)
extern "C" unsigned char _BitScanForward64(unsigned long* _Index, unsigned __int64 _Mask);
# pragma intrinsic(_BitScanForward64)
# endif // BX_ARCH_64BIT
#endif // BX_COMPILER_MSVC
namespace bx
{
inline BX_CONSTEXPR_FUNC float toRad(float _deg)
@@ -581,6 +597,16 @@ namespace bx
#if BX_COMPILER_GCC || BX_COMPILER_CLANG
return 0 == _val ? 32 : __builtin_clz(_val);
#else
# if BX_COMPILER_MSVC
if (!isConstantEvaluated() )
{
unsigned long index;
return 0 != _BitScanReverse(&index, (unsigned long)_val)
? uint8_t(31 - index)
: uint8_t(32)
;
}
# endif // BX_COMPILER_MSVC
const uint32_t tmp0 = uint32_srl(_val, 1);
const uint32_t tmp1 = uint32_or(tmp0, _val);
const uint32_t tmp2 = uint32_srl(tmp1, 2);
@@ -604,6 +630,16 @@ namespace bx
#if BX_COMPILER_GCC || BX_COMPILER_CLANG
return 0 == _val ? 64 : __builtin_clzll(_val);
#else
# if BX_COMPILER_MSVC && BX_ARCH_64BIT
if (!isConstantEvaluated() )
{
unsigned long index;
return 0 != _BitScanReverse64(&index, (unsigned __int64)_val)
? uint8_t(63 - index)
: uint8_t(64)
;
}
# endif // BX_COMPILER_MSVC && BX_ARCH_64BIT
return _val & UINT64_C(0xffffffff00000000)
? countLeadingZeros<uint32_t>(uint32_t(_val>>32) )
: countLeadingZeros<uint32_t>(uint32_t(_val) ) + 32
@@ -630,6 +666,16 @@ namespace bx
#if BX_COMPILER_GCC || BX_COMPILER_CLANG
return 0 == _val ? 32 : __builtin_ctz(_val);
#else
# if BX_COMPILER_MSVC
if (!isConstantEvaluated() )
{
unsigned long index;
return 0 != _BitScanForward(&index, (unsigned long)_val)
? uint8_t(index)
: uint8_t(32)
;
}
# endif // BX_COMPILER_MSVC
const uint32_t tmp0 = uint32_not(_val);
const uint32_t tmp1 = uint32_dec(_val);
const uint32_t tmp2 = uint32_and(tmp0, tmp1);
@@ -645,6 +691,16 @@ namespace bx
#if BX_COMPILER_GCC || BX_COMPILER_CLANG
return 0 == _val ? 64 : __builtin_ctzll(_val);
#else
# if BX_COMPILER_MSVC && BX_ARCH_64BIT
if (!isConstantEvaluated() )
{
unsigned long index;
return 0 != _BitScanForward64(&index, (unsigned __int64)_val)
? uint8_t(index)
: uint8_t(64)
;
}
# endif // BX_COMPILER_MSVC && BX_ARCH_64BIT
return _val & UINT64_C(0xffffffff)
? countTrailingZeros<uint32_t>(uint32_t(_val) )
: countTrailingZeros<uint32_t>(uint32_t(_val>>32) ) + 32