/*-------------------------------------------------------------------------
 *
 * pg_bitutils.c
 *	  Miscellaneous functions for bit-wise operations.
 *
 * Copyright (c) 2019-2026, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *	  src/port/pg_bitutils.c
 *
 *-------------------------------------------------------------------------
 */
#include "c.h"

#include "port/pg_bitutils.h"


/*
 * Array giving the position of the left-most set bit for each possible
 * byte value.  We count the right-most position as the 0th bit, and the
 * left-most the 7th bit.  The 0th entry of the array should not be used.
 *
 * Note: this is not used by the functions in pg_bitutils.h when
 * HAVE__BUILTIN_CLZ is defined, but we provide it anyway, so that
 * extensions possibly compiled with a different compiler can use it.
 */
const uint8 pg_leftmost_one_pos[256] = {
	0, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
	4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
	5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
	5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
	6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
	6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
	6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
	6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7
};

/*
 * Array giving the position of the right-most set bit for each possible
 * byte value.  We count the right-most position as the 0th bit, and the
 * left-most the 7th bit.  The 0th entry of the array should not be used.
 *
 * Note: this is not used by the functions in pg_bitutils.h when
 * HAVE__BUILTIN_CTZ is defined, but we provide it anyway, so that
 * extensions possibly compiled with a different compiler can use it.
 */
const uint8 pg_rightmost_one_pos[256] = {
	0, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	6, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	7, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	6, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
	4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
};

/*
 * Array giving the number of 1-bits in each possible byte value.
 *
 * Note: we export this for use by functions in which explicit use
 * of the popcount functions seems unlikely to be a win.
 */
const uint8 pg_number_of_ones[256] = {
	0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
	1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
	1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
	2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
	1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
	2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
	2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
	3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
	1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
	2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
	2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
	3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
	2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
	3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
	3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
	4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8
};

/*
 * pg_popcount_portable
 *		Returns the number of 1-bits in buf
 */
uint64
pg_popcount_portable(const char *buf, int bytes)
{
	uint64		popcnt = 0;

#if SIZEOF_VOID_P >= 8
	/* Process in 64-bit chunks if the buffer is aligned. */
	if (buf == (const char *) TYPEALIGN(8, buf))
	{
		const uint64 *words = (const uint64 *) buf;

		while (bytes >= 8)
		{
			popcnt += pg_popcount64(*words++);
			bytes -= 8;
		}

		buf = (const char *) words;
	}
#endif

	/* Process any remaining bytes */
	while (bytes--)
		popcnt += pg_number_of_ones[(unsigned char) *buf++];

	return popcnt;
}

/*
 * pg_popcount_masked_portable
 *		Returns the number of 1-bits in buf after applying the mask to each byte
 */
uint64
pg_popcount_masked_portable(const char *buf, int bytes, uint8 mask)
{
	uint64		popcnt = 0;

#if SIZEOF_VOID_P >= 8
	/* Process in 64-bit chunks if the buffer is aligned */
	uint64		maskv = ~UINT64CONST(0) / 0xFF * mask;

	if (buf == (const char *) TYPEALIGN(8, buf))
	{
		const uint64 *words = (const uint64 *) buf;

		while (bytes >= 8)
		{
			popcnt += pg_popcount64(*words++ & maskv);
			bytes -= 8;
		}

		buf = (const char *) words;
	}
#endif

	/* Process any remaining bytes */
	while (bytes--)
		popcnt += pg_number_of_ones[(unsigned char) *buf++ & mask];

	return popcnt;
}

#if !defined(HAVE_X86_64_POPCNTQ) && !defined(USE_NEON)

/*
 * When special CPU instructions are not available, there's no point in using
 * function pointers to vary the implementation.  We instead just make these
 * actual external functions.  The compiler should be able to inline the
 * portable versions here.
 */

/*
 * pg_popcount_optimized
 *		Returns the number of 1-bits in buf
 */
uint64
pg_popcount_optimized(const char *buf, int bytes)
{
	return pg_popcount_portable(buf, bytes);
}

/*
 * pg_popcount_masked_optimized
 *		Returns the number of 1-bits in buf after applying the mask to each byte
 */
uint64
pg_popcount_masked_optimized(const char *buf, int bytes, uint8 mask)
{
	return pg_popcount_masked_portable(buf, bytes, mask);
}

#endif							/* ! HAVE_X86_64_POPCNTQ && ! USE_NEON */
