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/*-------------------------------------------------------------------------
*
* pg_bitutils.h
* Miscellaneous functions for bit-wise operations.
*
*
* Copyright (c) 2019-2020, PostgreSQL Global Development Group
*
* src/include/port/pg_bitutils.h
*
*-------------------------------------------------------------------------
*/
#ifndef PG_BITUTILS_H
#define PG_BITUTILS_H
#ifndef FRONTEND
extern PGDLLIMPORT const uint8 pg_leftmost_one_pos[256];
extern PGDLLIMPORT const uint8 pg_rightmost_one_pos[256];
extern PGDLLIMPORT const uint8 pg_number_of_ones[256];
#else
extern const uint8 pg_leftmost_one_pos[256];
extern const uint8 pg_rightmost_one_pos[256];
extern const uint8 pg_number_of_ones[256];
#endif
/*
* pg_leftmost_one_pos32
* Returns the position of the most significant set bit in "word",
* measured from the least significant bit. word must not be 0.
*/
static inline int
pg_leftmost_one_pos32(uint32 word)
{
#ifdef HAVE__BUILTIN_CLZ
Assert(word != 0);
return 31 - __builtin_clz(word);
#else
int shift = 32 - 8;
Assert(word != 0);
while ((word >> shift) == 0)
shift -= 8;
return shift + pg_leftmost_one_pos[(word >> shift) & 255];
#endif /* HAVE__BUILTIN_CLZ */
}
/*
* pg_leftmost_one_pos64
* As above, but for a 64-bit word.
*/
static inline int
pg_leftmost_one_pos64(uint64 word)
{
#ifdef HAVE__BUILTIN_CLZ
Assert(word != 0);
#if defined(HAVE_LONG_INT_64)
return 63 - __builtin_clzl(word);
#elif defined(HAVE_LONG_LONG_INT_64)
return 63 - __builtin_clzll(word);
#else
#error must have a working 64-bit integer datatype
#endif
#else /* !HAVE__BUILTIN_CLZ */
int shift = 64 - 8;
Assert(word != 0);
while ((word >> shift) == 0)
shift -= 8;
return shift + pg_leftmost_one_pos[(word >> shift) & 255];
#endif /* HAVE__BUILTIN_CLZ */
}
/*
* pg_rightmost_one_pos32
* Returns the position of the least significant set bit in "word",
* measured from the least significant bit. word must not be 0.
*/
static inline int
pg_rightmost_one_pos32(uint32 word)
{
#ifdef HAVE__BUILTIN_CTZ
Assert(word != 0);
return __builtin_ctz(word);
#else
int result = 0;
Assert(word != 0);
while ((word & 255) == 0)
{
word >>= 8;
result += 8;
}
result += pg_rightmost_one_pos[word & 255];
return result;
#endif /* HAVE__BUILTIN_CTZ */
}
/*
* pg_rightmost_one_pos64
* As above, but for a 64-bit word.
*/
static inline int
pg_rightmost_one_pos64(uint64 word)
{
#ifdef HAVE__BUILTIN_CTZ
Assert(word != 0);
#if defined(HAVE_LONG_INT_64)
return __builtin_ctzl(word);
#elif defined(HAVE_LONG_LONG_INT_64)
return __builtin_ctzll(word);
#else
#error must have a working 64-bit integer datatype
#endif
#else /* !HAVE__BUILTIN_CTZ */
int result = 0;
Assert(word != 0);
while ((word & 255) == 0)
{
word >>= 8;
result += 8;
}
result += pg_rightmost_one_pos[word & 255];
return result;
#endif /* HAVE__BUILTIN_CTZ */
}
/*
* pg_nextpower2_32
* Returns the next highest power of 2 of 'num', or 'num', if it's
* already a power of 2.
*
* 'num' mustn't be 0 or be above PG_UINT32_MAX / 2 + 1.
*/
static inline uint32
pg_nextpower2_32(uint32 num)
{
Assert(num > 0 && num <= PG_UINT32_MAX / 2 + 1);
/*
* A power 2 number has only 1 bit set. Subtracting 1 from such a number
* will turn on all previous bits resulting in no common bits being set
* between num and num-1.
*/
if ((num & (num - 1)) == 0)
return num; /* already power 2 */
return ((uint32) 1) << (pg_leftmost_one_pos32(num) + 1);
}
/*
* pg_nextpower2_64
* Returns the next highest power of 2 of 'num', or 'num', if it's
* already a power of 2.
*
* 'num' mustn't be 0 or be above PG_UINT64_MAX / 2 + 1.
*/
static inline uint64
pg_nextpower2_64(uint64 num)
{
Assert(num > 0 && num <= PG_UINT64_MAX / 2 + 1);
/*
* A power 2 number has only 1 bit set. Subtracting 1 from such a number
* will turn on all previous bits resulting in no common bits being set
* between num and num-1.
*/
if ((num & (num - 1)) == 0)
return num; /* already power 2 */
return ((uint64) 1) << (pg_leftmost_one_pos64(num) + 1);
}
/*
* pg_ceil_log2_32
* Returns equivalent of ceil(log2(num))
*/
static inline uint32
pg_ceil_log2_32(uint32 num)
{
if (num < 2)
return 0;
else
return pg_leftmost_one_pos32(num - 1) + 1;
}
/*
* pg_ceil_log2_64
* Returns equivalent of ceil(log2(num))
*/
static inline uint64
pg_ceil_log2_64(uint64 num)
{
if (num < 2)
return 0;
else
return pg_leftmost_one_pos64(num - 1) + 1;
}
/* Count the number of one-bits in a uint32 or uint64 */
extern int (*pg_popcount32) (uint32 word);
extern int (*pg_popcount64) (uint64 word);
/* Count the number of one-bits in a byte array */
extern uint64 pg_popcount(const char *buf, int bytes);
/*
* Rotate the bits of "word" to the right by n bits.
*/
static inline uint32
pg_rotate_right32(uint32 word, int n)
{
return (word >> n) | (word << (sizeof(word) * BITS_PER_BYTE - n));
}
#endif /* PG_BITUTILS_H */
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