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329 lines
7.4 KiB
C
329 lines
7.4 KiB
C
/*-------------------------------------------------------------------------
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*
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* pg_bitutils.h
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* Miscellaneous functions for bit-wise operations.
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*
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*
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* Copyright (c) 2019-2023, PostgreSQL Global Development Group
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*
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* src/include/port/pg_bitutils.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef PG_BITUTILS_H
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#define PG_BITUTILS_H
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extern PGDLLIMPORT const uint8 pg_leftmost_one_pos[256];
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extern PGDLLIMPORT const uint8 pg_rightmost_one_pos[256];
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extern PGDLLIMPORT const uint8 pg_number_of_ones[256];
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/*
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* pg_leftmost_one_pos32
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* Returns the position of the most significant set bit in "word",
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* measured from the least significant bit. word must not be 0.
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*/
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static inline int
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pg_leftmost_one_pos32(uint32 word)
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{
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#ifdef HAVE__BUILTIN_CLZ
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int bitscan_result;
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#endif
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#if !defined(HAVE__BUILTIN_CLZ) || defined(USE_ASSERT_CHECKING)
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int result;
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int shift = 32 - 8;
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Assert(word != 0);
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while ((word >> shift) == 0)
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shift -= 8;
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result = shift + pg_leftmost_one_pos[(word >> shift) & 255];
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#endif
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#if defined(HAVE__BUILTIN_CLZ)
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bitscan_result = 31 - __builtin_clz(word);
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Assert(bitscan_result == result);
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return bitscan_result;
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#else
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return result;
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#endif /* HAVE__BUILTIN_CLZ */
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}
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/*
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* pg_leftmost_one_pos64
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* As above, but for a 64-bit word.
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*/
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static inline int
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pg_leftmost_one_pos64(uint64 word)
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{
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#ifdef HAVE__BUILTIN_CLZ
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int bitscan_result;
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#endif
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#if !defined(HAVE__BUILTIN_CLZ) || defined(USE_ASSERT_CHECKING)
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int result;
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int shift = 64 - 8;
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Assert(word != 0);
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while ((word >> shift) == 0)
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shift -= 8;
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result = shift + pg_leftmost_one_pos[(word >> shift) & 255];
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#endif
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#if defined(HAVE__BUILTIN_CLZ)
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#if defined(HAVE_LONG_INT_64)
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bitscan_result = 63 - __builtin_clzl(word);
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#elif defined(HAVE_LONG_LONG_INT_64)
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bitscan_result = 63 - __builtin_clzll(word);
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#else
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#error must have a working 64-bit integer datatype
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#endif /* HAVE_LONG_INT_64 */
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Assert(bitscan_result == result);
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return bitscan_result;
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#else
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return result;
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#endif /* HAVE__BUILTIN_CLZ */
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}
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/*
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* pg_rightmost_one_pos32
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* Returns the position of the least significant set bit in "word",
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* measured from the least significant bit. word must not be 0.
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*/
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static inline int
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pg_rightmost_one_pos32(uint32 word)
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{
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#ifdef HAVE__BUILTIN_CTZ
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const uint32 orig_word = word;
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int bitscan_result;
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#endif
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#if !defined(HAVE__BUILTIN_CTZ) || defined(USE_ASSERT_CHECKING)
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int result = 0;
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Assert(word != 0);
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while ((word & 255) == 0)
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{
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word >>= 8;
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result += 8;
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}
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result += pg_rightmost_one_pos[word & 255];
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#endif
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#if defined(HAVE__BUILTIN_CTZ)
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bitscan_result = __builtin_ctz(orig_word);
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Assert(bitscan_result == result);
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return bitscan_result;
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#else
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return result;
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#endif /* HAVE__BUILTIN_CTZ */
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}
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/*
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* pg_rightmost_one_pos64
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* As above, but for a 64-bit word.
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*/
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static inline int
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pg_rightmost_one_pos64(uint64 word)
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{
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#ifdef HAVE__BUILTIN_CTZ
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const uint64 orig_word = word;
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int bitscan_result;
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#endif
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#if !defined(HAVE__BUILTIN_CTZ) || defined(USE_ASSERT_CHECKING)
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int result = 0;
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Assert(word != 0);
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while ((word & 255) == 0)
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{
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word >>= 8;
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result += 8;
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}
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result += pg_rightmost_one_pos[word & 255];
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#endif
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#if defined(HAVE__BUILTIN_CTZ)
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#if defined(HAVE_LONG_INT_64)
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bitscan_result = __builtin_ctzl(orig_word);
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#elif defined(HAVE_LONG_LONG_INT_64)
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bitscan_result = __builtin_ctzll(orig_word);
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#else
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#error must have a working 64-bit integer datatype
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#endif /* HAVE_LONG_INT_64 */
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Assert(bitscan_result == result);
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return bitscan_result;
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#else
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return result;
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#endif /* HAVE__BUILTIN_CTZ */
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}
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/*
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* pg_nextpower2_32
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* Returns the next higher power of 2 above 'num', or 'num' if it's
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* already a power of 2.
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*
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* 'num' mustn't be 0 or be above PG_UINT32_MAX / 2 + 1.
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*/
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static inline uint32
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pg_nextpower2_32(uint32 num)
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{
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Assert(num > 0 && num <= PG_UINT32_MAX / 2 + 1);
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/*
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* A power 2 number has only 1 bit set. Subtracting 1 from such a number
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* will turn on all previous bits resulting in no common bits being set
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* between num and num-1.
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*/
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if ((num & (num - 1)) == 0)
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return num; /* already power 2 */
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return ((uint32) 1) << (pg_leftmost_one_pos32(num) + 1);
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}
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/*
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* pg_nextpower2_64
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* Returns the next higher power of 2 above 'num', or 'num' if it's
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* already a power of 2.
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*
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* 'num' mustn't be 0 or be above PG_UINT64_MAX / 2 + 1.
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*/
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static inline uint64
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pg_nextpower2_64(uint64 num)
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{
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Assert(num > 0 && num <= PG_UINT64_MAX / 2 + 1);
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/*
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* A power 2 number has only 1 bit set. Subtracting 1 from such a number
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* will turn on all previous bits resulting in no common bits being set
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* between num and num-1.
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*/
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if ((num & (num - 1)) == 0)
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return num; /* already power 2 */
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return ((uint64) 1) << (pg_leftmost_one_pos64(num) + 1);
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}
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/*
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* pg_prevpower2_32
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* Returns the next lower power of 2 below 'num', or 'num' if it's
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* already a power of 2.
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*
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* 'num' mustn't be 0.
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*/
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static inline uint32
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pg_prevpower2_32(uint32 num)
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{
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return ((uint32) 1) << pg_leftmost_one_pos32(num);
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}
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/*
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* pg_prevpower2_64
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* Returns the next lower power of 2 below 'num', or 'num' if it's
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* already a power of 2.
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*
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* 'num' mustn't be 0.
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*/
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static inline uint64
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pg_prevpower2_64(uint64 num)
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{
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return ((uint64) 1) << pg_leftmost_one_pos64(num);
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}
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/*
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* pg_ceil_log2_32
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* Returns equivalent of ceil(log2(num))
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*/
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static inline uint32
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pg_ceil_log2_32(uint32 num)
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{
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if (num < 2)
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return 0;
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else
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return pg_leftmost_one_pos32(num - 1) + 1;
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}
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/*
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* pg_ceil_log2_64
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* Returns equivalent of ceil(log2(num))
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*/
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static inline uint64
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pg_ceil_log2_64(uint64 num)
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{
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if (num < 2)
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return 0;
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else
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return pg_leftmost_one_pos64(num - 1) + 1;
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}
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/*
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* With MSVC on x86_64 builds, try using native popcnt instructions via the
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* __popcnt and __popcnt64 intrinsics. These don't work the same as GCC's
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* __builtin_popcount* intrinsic functions as they always emit popcnt
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* instructions.
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*/
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#if defined(_MSC_VER) && defined(_M_AMD64)
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#define HAVE_X86_64_POPCNTQ
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#endif
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/*
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* On x86_64, we can use the hardware popcount instruction, but only if
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* we can verify that the CPU supports it via the cpuid instruction.
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*
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* Otherwise, we fall back to a hand-rolled implementation.
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*/
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#ifdef HAVE_X86_64_POPCNTQ
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#if defined(HAVE__GET_CPUID) || defined(HAVE__CPUID)
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#define TRY_POPCNT_FAST 1
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#endif
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#endif
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#ifdef TRY_POPCNT_FAST
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/* Attempt to use the POPCNT instruction, but perform a runtime check first */
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extern int (*pg_popcount32) (uint32 word);
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extern int (*pg_popcount64) (uint64 word);
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#else
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/* Use a portable implementation -- no need for a function pointer. */
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extern int pg_popcount32(uint32 word);
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extern int pg_popcount64(uint64 word);
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#endif /* TRY_POPCNT_FAST */
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/* Count the number of one-bits in a byte array */
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extern uint64 pg_popcount(const char *buf, int bytes);
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/*
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* Rotate the bits of "word" to the right/left by n bits.
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*/
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static inline uint32
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pg_rotate_right32(uint32 word, int n)
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{
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return (word >> n) | (word << (32 - n));
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}
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static inline uint32
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pg_rotate_left32(uint32 word, int n)
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{
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return (word << n) | (word >> (32 - n));
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}
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/* size_t variants of the above, as required */
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#if SIZEOF_SIZE_T == 4
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#define pg_leftmost_one_pos_size_t pg_leftmost_one_pos32
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#define pg_nextpower2_size_t pg_nextpower2_32
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#define pg_prevpower2_size_t pg_prevpower2_32
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#else
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#define pg_leftmost_one_pos_size_t pg_leftmost_one_pos64
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#define pg_nextpower2_size_t pg_nextpower2_64
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#define pg_prevpower2_size_t pg_prevpower2_64
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#endif
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#endif /* PG_BITUTILS_H */
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