pg_bitutils.c

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/*-------------------------------------------------------------------------
 *
 * pg_bitutils.c
 *    Miscellaneous functions for bit-wise operations.
 *
 * Copyright (c) 2019-2023, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/port/pg_bitutils.c
 *
 *-------------------------------------------------------------------------
 */
#include "c.h"
 
#ifdef HAVE__GET_CPUID
#include <cpuid.h>
#endif
#ifdef HAVE__CPUID
#include <intrin.h>
#endif
 
#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
};
 
static int  pg_popcount32_slow(uint32 word);
static int  pg_popcount64_slow(uint64 word);
 
#ifdef TRY_POPCNT_FAST
static bool pg_popcount_available(void);
static int  pg_popcount32_choose(uint32 word);
static int  pg_popcount64_choose(uint64 word);
static int  pg_popcount32_fast(uint32 word);
static int  pg_popcount64_fast(uint64 word);
 
int         (*pg_popcount32) (uint32 word) = pg_popcount32_choose;
int         (*pg_popcount64) (uint64 word) = pg_popcount64_choose;
#endif                          /* TRY_POPCNT_FAST */
 
#ifdef TRY_POPCNT_FAST
 
/*
 * Return true if CPUID indicates that the POPCNT instruction is available.
 */
static bool
pg_popcount_available(void)
{
    unsigned int exx[4] = {0, 0, 0, 0};
 
#if defined(HAVE__GET_CPUID)
    __get_cpuid(1, &exx[0], &exx[1], &exx[2], &exx[3]);
#elif defined(HAVE__CPUID)
    __cpuid(exx, 1);
#else
#error cpuid instruction not available
#endif
 
    return (exx[2] & (1 << 23)) != 0;   /* POPCNT */
}
 
/*
 * These functions get called on the first call to pg_popcount32 etc.
 * They detect whether we can use the asm implementations, and replace
 * the function pointers so that subsequent calls are routed directly to
 * the chosen implementation.
 */
static int
pg_popcount32_choose(uint32 word)
{
    if (pg_popcount_available())
    {
        pg_popcount32 = pg_popcount32_fast;
        pg_popcount64 = pg_popcount64_fast;
    }
    else
    {
        pg_popcount32 = pg_popcount32_slow;
        pg_popcount64 = pg_popcount64_slow;
    }
 
    return pg_popcount32(word);
}
 
static int
pg_popcount64_choose(uint64 word)
{
    if (pg_popcount_available())
    {
        pg_popcount32 = pg_popcount32_fast;
        pg_popcount64 = pg_popcount64_fast;
    }
    else
    {
        pg_popcount32 = pg_popcount32_slow;
        pg_popcount64 = pg_popcount64_slow;
    }
 
    return pg_popcount64(word);
}
 
/*
 * pg_popcount32_fast
 *      Return the number of 1 bits set in word
 */
static int
pg_popcount32_fast(uint32 word)
{
#ifdef _MSC_VER
    return __popcnt(word);
#else
    uint32      res;
 
__asm__ __volatile__(" popcntl %1,%0\n":"=q"(res):"rm"(word):"cc");
    return (int) res;
#endif
}
 
/*
 * pg_popcount64_fast
 *      Return the number of 1 bits set in word
 */
static int
pg_popcount64_fast(uint64 word)
{
#ifdef _MSC_VER
    return __popcnt64(word);
#else
    uint64      res;
 
__asm__ __volatile__(" popcntq %1,%0\n":"=q"(res):"rm"(word):"cc");
    return (int) res;
#endif
}
 
#endif                          /* TRY_POPCNT_FAST */
 
 
/*
 * pg_popcount32_slow
 *      Return the number of 1 bits set in word
 */
static int
pg_popcount32_slow(uint32 word)
{
#ifdef HAVE__BUILTIN_POPCOUNT
    return __builtin_popcount(word);
#else                           /* !HAVE__BUILTIN_POPCOUNT */
    int         result = 0;
 
    while (word != 0)
    {
        result += pg_number_of_ones[word & 255];
        word >>= 8;
    }
 
    return result;
#endif                          /* HAVE__BUILTIN_POPCOUNT */
}
 
/*
 * pg_popcount64_slow
 *      Return the number of 1 bits set in word
 */
static int
pg_popcount64_slow(uint64 word)
{
#ifdef HAVE__BUILTIN_POPCOUNT
#if defined(HAVE_LONG_INT_64)
    return __builtin_popcountl(word);
#elif defined(HAVE_LONG_LONG_INT_64)
    return __builtin_popcountll(word);
#else
#error must have a working 64-bit integer datatype
#endif
#else                           /* !HAVE__BUILTIN_POPCOUNT */
    int         result = 0;
 
    while (word != 0)
    {
        result += pg_number_of_ones[word & 255];
        word >>= 8;
    }
 
    return result;
#endif                          /* HAVE__BUILTIN_POPCOUNT */
}
 
#ifndef TRY_POPCNT_FAST
 
/*
 * When the POPCNT instruction is not available, there's no point in using
 * function pointers to vary the implementation between the fast and slow
 * method.  We instead just make these actual external functions when
 * TRY_POPCNT_FAST is not defined.  The compiler should be able to inline
 * the slow versions here.
 */
int
pg_popcount32(uint32 word)
{
    return pg_popcount32_slow(word);
}
 
int
pg_popcount64(uint64 word)
{
    return pg_popcount64_slow(word);
}
 
#endif                          /* !TRY_POPCNT_FAST */
 
/*
 * pg_popcount
 *      Returns the number of 1-bits in buf
 */
uint64
pg_popcount(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;
    }
#else
    /* Process in 32-bit chunks if the buffer is aligned. */
    if (buf == (const char *) TYPEALIGN(4, buf))
    {
        const uint32 *words = (const uint32 *) buf;
 
        while (bytes >= 4)
        {
            popcnt += pg_popcount32(*words++);
            bytes -= 4;
        }
 
        buf = (const char *) words;
    }
#endif
 
    /* Process any remaining bytes */
    while (bytes--)
        popcnt += pg_number_of_ones[(unsigned char) *buf++];
 
    return popcnt;
}