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Diffstat (limited to 'contrib/zstd/bits.h')
| -rw-r--r-- | contrib/zstd/bits.h | 175 |
1 files changed, 175 insertions, 0 deletions
diff --git a/contrib/zstd/bits.h b/contrib/zstd/bits.h new file mode 100644 index 0000000..7939f3d --- /dev/null +++ b/contrib/zstd/bits.h @@ -0,0 +1,175 @@ +/* + * Copyright (c) Meta Platforms, Inc. and affiliates. + * All rights reserved. + * + * This source code is licensed under both the BSD-style license (found in the + * LICENSE file in the root directory of this source tree) and the GPLv2 (found + * in the COPYING file in the root directory of this source tree). + * You may select, at your option, one of the above-listed licenses. + */ + +#ifndef ZSTD_BITS_H +#define ZSTD_BITS_H + +#include "mem.h" + +MEM_STATIC unsigned ZSTD_countTrailingZeros32_fallback(U32 val) +{ + assert(val != 0); + { + static const int DeBruijnBytePos[32] = {0, 1, 28, 2, 29, 14, 24, 3, + 30, 22, 20, 15, 25, 17, 4, 8, + 31, 27, 13, 23, 21, 19, 16, 7, + 26, 12, 18, 6, 11, 5, 10, 9}; + return DeBruijnBytePos[((U32) ((val & -(S32) val) * 0x077CB531U)) >> 27]; + } +} + +MEM_STATIC unsigned ZSTD_countTrailingZeros32(U32 val) +{ + assert(val != 0); +# if defined(_MSC_VER) +# if STATIC_BMI2 == 1 + return _tzcnt_u32(val); +# else + if (val != 0) { + unsigned long r; + _BitScanForward(&r, val); + return (unsigned)r; + } else { + /* Should not reach this code path */ + __assume(0); + } +# endif +# elif defined(__GNUC__) && (__GNUC__ >= 4) + return (unsigned)__builtin_ctz(val); +# else + return ZSTD_countTrailingZeros32_fallback(val); +# endif +} + +MEM_STATIC unsigned ZSTD_countLeadingZeros32_fallback(U32 val) { + assert(val != 0); + { + static const U32 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}; + val |= val >> 1; + val |= val >> 2; + val |= val >> 4; + val |= val >> 8; + val |= val >> 16; + return 31 - DeBruijnClz[(val * 0x07C4ACDDU) >> 27]; + } +} + +MEM_STATIC unsigned ZSTD_countLeadingZeros32(U32 val) +{ + assert(val != 0); +# if defined(_MSC_VER) +# if STATIC_BMI2 == 1 + return _lzcnt_u32(val); +# else + if (val != 0) { + unsigned long r; + _BitScanReverse(&r, val); + return (unsigned)(31 - r); + } else { + /* Should not reach this code path */ + __assume(0); + } +# endif +# elif defined(__GNUC__) && (__GNUC__ >= 4) + return (unsigned)__builtin_clz(val); +# else + return ZSTD_countLeadingZeros32_fallback(val); +# endif +} + +MEM_STATIC unsigned ZSTD_countTrailingZeros64(U64 val) +{ + assert(val != 0); +# if defined(_MSC_VER) && defined(_WIN64) +# if STATIC_BMI2 == 1 + return _tzcnt_u64(val); +# else + if (val != 0) { + unsigned long r; + _BitScanForward64(&r, val); + return (unsigned)r; + } else { + /* Should not reach this code path */ + __assume(0); + } +# endif +# elif defined(__GNUC__) && (__GNUC__ >= 4) && defined(__LP64__) + return (unsigned)__builtin_ctzll(val); +# else + { + U32 mostSignificantWord = (U32)(val >> 32); + U32 leastSignificantWord = (U32)val; + if (leastSignificantWord == 0) { + return 32 + ZSTD_countTrailingZeros32(mostSignificantWord); + } else { + return ZSTD_countTrailingZeros32(leastSignificantWord); + } + } +# endif +} + +MEM_STATIC unsigned ZSTD_countLeadingZeros64(U64 val) +{ + assert(val != 0); +# if defined(_MSC_VER) && defined(_WIN64) +# if STATIC_BMI2 == 1 + return _lzcnt_u64(val); +# else + if (val != 0) { + unsigned long r; + _BitScanReverse64(&r, val); + return (unsigned)(63 - r); + } else { + /* Should not reach this code path */ + __assume(0); + } +# endif +# elif defined(__GNUC__) && (__GNUC__ >= 4) + return (unsigned)(__builtin_clzll(val)); +# else + { + U32 mostSignificantWord = (U32)(val >> 32); + U32 leastSignificantWord = (U32)val; + if (mostSignificantWord == 0) { + return 32 + ZSTD_countLeadingZeros32(leastSignificantWord); + } else { + return ZSTD_countLeadingZeros32(mostSignificantWord); + } + } +# endif +} + +MEM_STATIC unsigned ZSTD_NbCommonBytes(size_t val) +{ + if (MEM_isLittleEndian()) { + if (MEM_64bits()) { + return ZSTD_countTrailingZeros64((U64)val) >> 3; + } else { + return ZSTD_countTrailingZeros32((U32)val) >> 3; + } + } else { /* Big Endian CPU */ + if (MEM_64bits()) { + return ZSTD_countLeadingZeros64((U64)val) >> 3; + } else { + return ZSTD_countLeadingZeros32((U32)val) >> 3; + } + } +} + +MEM_STATIC unsigned ZSTD_highbit32(U32 val) /* compress, dictBuilder, decodeCorpus */ +{ + assert(val != 0); + return 31 - ZSTD_countLeadingZeros32(val); +} + +#endif /* ZSTD_BITS_H */ |