greenplumn pg_crc32c_sse42_choose 源码
greenplumn pg_crc32c_sse42_choose 代码
文件路径：/src/port/pg_crc32c_sse42_choose.c
/*-------------------------------------------------------------------------
*
* pg_crc32c_sse42_choose.c
* Choose between Intel SSE 4.2 and software CRC-32C implementation.
*
* On first call, checks if the CPU we're running on supports Intel SSE
* 4.2. If it does, use the special SSE instructions for CRC-32C
* computation. Otherwise, fall back to the pure software implementation
* (slicing-by-8).
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/port/pg_crc32c_sse42_choose.c
*
*-------------------------------------------------------------------------
*/
#include "c.h"
#ifdef HAVE__GET_CPUID
#include <cpuid.h>
#endif
#ifdef HAVE__CPUID
#include <intrin.h>
#endif
#include "port/pg_crc32c.h"
static bool
pg_crc32c_sse42_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 << 20)) != 0; /* SSE 4.2 */
}
/*
* This gets called on the first call. It replaces the function pointer
* so that subsequent calls are routed directly to the chosen implementation.
*/
static pg_crc32c
pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len)
{
if (pg_crc32c_sse42_available())
pg_comp_crc32c = pg_comp_crc32c_sse42;
else
pg_comp_crc32c = pg_comp_crc32c_sb8;
return pg_comp_crc32c(crc, data, len);
}
pg_crc32c (*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) = pg_comp_crc32c_choose;
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