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Code Issues Releases 1 Activity

Use clz ^ 31 instead of 31 - clz; better codegen for GCC

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This commit is contained in:
Dávid Bolvanský
2019-09-23 21:23:09 +02:00
parent 7451c6578c
commit 1f7228c040
8 changed files with 8 additions and 8 deletions
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2
lib/legacy/zstd_v01.c
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@@ -346,7 +346,7 @@ FORCE_INLINE unsigned FSE_highbit32 (U32 val)
_BitScanReverse ( &r, val );
return (unsigned) r;
# elif defined(__GNUC__) && (GCC_VERSION >= 304) /* GCC Intrinsic */
return 31 - __builtin_clz (val);
return __builtin_clz (val) ^ 31;
# else /* Software version */
static const unsigned DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31 };
U32 v = val;

2
lib/legacy/zstd_v02.c
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@@ -353,7 +353,7 @@ MEM_STATIC unsigned BIT_highbit32 (U32 val)
_BitScanReverse ( &r, val );
return (unsigned) r;
# elif defined(__GNUC__) && (__GNUC__ >= 3) /* Use GCC Intrinsic */
return 31 - __builtin_clz (val);
return __builtin_clz (val) ^ 31;
# else /* Software version */
static const unsigned DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31 };
U32 v = val;

2
lib/legacy/zstd_v03.c
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@@ -356,7 +356,7 @@ MEM_STATIC unsigned BIT_highbit32 (U32 val)
_BitScanReverse ( &r, val );
return (unsigned) r;
# elif defined(__GNUC__) && (__GNUC__ >= 3) /* Use GCC Intrinsic */
return 31 - __builtin_clz (val);
return __builtin_clz (val) ^ 31;
# else /* Software version */
static const unsigned DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31 };
U32 v = val;

2
lib/legacy/zstd_v04.c
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@@ -627,7 +627,7 @@ MEM_STATIC unsigned BIT_highbit32 (U32 val)
_BitScanReverse ( &r, val );
return (unsigned) r;
# elif defined(__GNUC__) && (__GNUC__ >= 3) /* Use GCC Intrinsic */
return 31 - __builtin_clz (val);
return __builtin_clz (val) ^ 31;
# else /* Software version */
static const unsigned DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31 };
U32 v = val;

2
lib/legacy/zstd_v05.c
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@@ -756,7 +756,7 @@ MEM_STATIC unsigned BITv05_highbit32 (U32 val)
_BitScanReverse ( &r, val );
return (unsigned) r;
# elif defined(__GNUC__) && (__GNUC__ >= 3) /* Use GCC Intrinsic */
return 31 - __builtin_clz (val);
return __builtin_clz (val) ^ 31;
# else /* Software version */
static const unsigned DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31 };
U32 v = val;

2
lib/legacy/zstd_v06.c
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@@ -860,7 +860,7 @@ MEM_STATIC unsigned BITv06_highbit32 ( U32 val)
_BitScanReverse ( &r, val );
return (unsigned) r;
# elif defined(__GNUC__) && (__GNUC__ >= 3) /* Use GCC Intrinsic */
return 31 - __builtin_clz (val);
return __builtin_clz (val) ^ 31;
# else /* Software version */
static const unsigned DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31 };
U32 v = val;

2
lib/legacy/zstd_v07.c
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@@ -530,7 +530,7 @@ MEM_STATIC unsigned BITv07_highbit32 (U32 val)
_BitScanReverse ( &r, val );
return (unsigned) r;
# elif defined(__GNUC__) && (__GNUC__ >= 3) /* Use GCC Intrinsic */
return 31 - __builtin_clz (val);
return __builtin_clz (val) ^ 31;
# else /* Software version */
static const unsigned DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31 };
U32 v = val;