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/*--------------------------------------------------------------------
* Symbols referenced in this file:
* - pg_popcount64
* - pg_popcount64_slow
*--------------------------------------------------------------------
*/
/*-------------------------------------------------------------------------
*
* pg_bitutils.c
* Miscellaneous functions for bit-wise operations.
*
* Copyright (c) 2019-2020, 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.
*/
/*
* 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.
*/
/*
* 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.
*/
/*
* On x86_64, we can use the hardware popcount instruction, but only if
* we can verify that the CPU supports it via the cpuid instruction.
*
* Otherwise, we fall back to __builtin_popcount if the compiler has that,
* or a hand-rolled implementation if not.
*/
#ifdef HAVE_X86_64_POPCNTQ
#if defined(HAVE__GET_CPUID) || defined(HAVE__CPUID)
#define USE_POPCNT_ASM 1
#endif
#endif
static int pg_popcount32_slow(uint32 word);
static int pg_popcount64_slow(uint64 word);
#ifdef USE_POPCNT_ASM
static bool pg_popcount_available(void);
static int pg_popcount32_choose(uint32 word);
static int pg_popcount64_choose(uint64 word);
static int pg_popcount32_asm(uint32 word);
static int pg_popcount64_asm(uint64 word);
int (*pg_popcount32) (uint32 word) = pg_popcount32_choose;
int (*pg_popcount64) (uint64 word) = pg_popcount64_choose;
#else
int (*pg_popcount64) (uint64 word) = pg_popcount64_slow;
#endif /* USE_POPCNT_ASM */
#ifdef USE_POPCNT_ASM
/*
* 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_asm;
pg_popcount64 = pg_popcount64_asm;
}
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_asm;
pg_popcount64 = pg_popcount64_asm;
}
else
{
pg_popcount32 = pg_popcount32_slow;
pg_popcount64 = pg_popcount64_slow;
}
return pg_popcount64(word);
}
/*
* pg_popcount32_asm
* Return the number of 1 bits set in word
*/
static int
pg_popcount32_asm(uint32 word)
{
uint32 res;
__asm__ __volatile__(" popcntl %1,%0\n":"=q"(res):"rm"(word):"cc");
return (int) res;
}
/*
* pg_popcount64_asm
* Return the number of 1 bits set in word
*/
static int
pg_popcount64_asm(uint64 word)
{
uint64 res;
__asm__ __volatile__(" popcntq %1,%0\n":"=q"(res):"rm"(word):"cc");
return (int) res;
}
#endif /* USE_POPCNT_ASM */
/*
* pg_popcount32_slow
* Return the number of 1 bits set in word
*/
#ifdef HAVE__BUILTIN_POPCOUNT
#else /* !HAVE__BUILTIN_POPCOUNT */
#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 */
}
/*
* pg_popcount
* Returns the number of 1-bits in buf
*/
#if SIZEOF_VOID_P >= 8
#else
#endif
|
