postgresql/src/include/port/pg_bitutils.h

/*-------------------------------------------------------------------------
 *
 * pg_bitutils.h
 *	  Miscellaneous functions for bit-wise operations.
 *
 *
 * Copyright (c) 2019, PostgreSQL Global Development Group
 *
 * src/include/port/pg_bitutils.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef PG_BITUTILS_H
#define PG_BITUTILS_H

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];

/*
 * 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__BUIILTIN_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 */
}

/* 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);

#endif							/* PG_BITUTILS_H */