Line data    Source code

       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * pg_crc32c_choose.c
       4             :  *    Choose which CRC-32C implementation to use, at runtime.
       5             :  *
       6             :  * Try to the special CRC instructions introduced in Intel SSE 4.2,
       7             :  * if available on the platform we're running on, but fall back to the
       8             :  * slicing-by-8 implementation otherwise.
       9             :  *
      10             :  * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
      11             :  * Portions Copyright (c) 1994, Regents of the University of California
      12             :  *
      13             :  *
      14             :  * IDENTIFICATION
      15             :  *    src/port/pg_crc32c_choose.c
      16             :  *
      17             :  *-------------------------------------------------------------------------
      18             :  */
      19             : 
      20             : #include "c.h"
      21             : 
      22             : #ifdef HAVE__GET_CPUID
      23             : #include <cpuid.h>
      24             : #endif
      25             : 
      26             : #ifdef HAVE__CPUID
      27             : #include <intrin.h>
      28             : #endif
      29             : 
      30             : #include "port/pg_crc32c.h"
      31             : 
      32             : static bool
      33           3 : pg_crc32c_sse42_available(void)
      34             : {
      35           3 :     unsigned int exx[4] = {0, 0, 0, 0};
      36             : 
      37             : #if defined(HAVE__GET_CPUID)
      38           3 :     __get_cpuid(1, &exx[0], &exx[1], &exx[2], &exx[3]);
      39             : #elif defined(HAVE__CPUID)
      40             :     __cpuid(exx, 1);
      41             : #else
      42             : #error cpuid instruction not available
      43             : #endif
      44             : 
      45           3 :     return (exx[2] & (1 << 20)) != 0; /* SSE 4.2 */
      46             : }
      47             : 
      48             : /*
      49             :  * This gets called on the first call. It replaces the function pointer
      50             :  * so that subsequent calls are routed directly to the chosen implementation.
      51             :  */
      52             : static pg_crc32c
      53           3 : pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len)
      54             : {
      55           3 :     if (pg_crc32c_sse42_available())
      56           3 :         pg_comp_crc32c = pg_comp_crc32c_sse42;
      57             :     else
      58           0 :         pg_comp_crc32c = pg_comp_crc32c_sb8;
      59             : 
      60           3 :     return pg_comp_crc32c(crc, data, len);
      61             : }
      62             : 
      63             : pg_crc32c   (*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) = pg_comp_crc32c_choose;