Less compiler errors in pg_crc32c_sse42_choose.c

Thu, 17 Jun 2021 02:29:57 -0700

I am just quoting the whole file here for simplicity, as its small


In line #43 the compiler errors out, if there is no cpuid.h or intrin.h available. As the code is supposed to 
fallback on a CRC software implementation, if SSE isn't available, returning false here instead, would be better. 


Ciao
   Nat!

```
   1 /*-------------------------------------------------------------------------
   2  *
   3  * pg_crc32c_sse42_choose.c
   4  *    Choose between Intel SSE 4.2 and software CRC-32C implementation.
   5  *
   6  * On first call, checks if the CPU we're running on supports Intel SSE
   7  * 4.2. If it does, use the special SSE instructions for CRC-32C
   8  * computation. Otherwise, fall back to the pure software implementation
   9  * (slicing-by-8).
  10  *
  11  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
  12  * Portions Copyright (c) 1994, Regents of the University of California
  13  *
  14  *
  15  * IDENTIFICATION
  16  *    src/port/pg_crc32c_sse42_choose.c
  17  *
  18  *-------------------------------------------------------------------------
  19  */
  20 
  21 #include "c.h"
  22 
  23 #ifdef HAVE__GET_CPUID
  24 #include <cpuid.h>
  25 #endif
  26 
  27 #ifdef HAVE__CPUID
  28 #include <intrin.h>
  29 #endif
  30 
  31 #include "port/pg_crc32c.h"
  32 
  33 static bool
  34 pg_crc32c_sse42_available(void)
  35 {
  36     unsigned int exx[4] = {0, 0, 0, 0};
  37 
  38 #if defined(HAVE__GET_CPUID)
  39     __get_cpuid(1, &exx[0], &exx[1], &exx[2], &exx[3]);
  40 #elif defined(HAVE__CPUID)
  41     __cpuid(exx, 1);
  42 #else
  43 #error cpuid instruction not available
  44 #endif
  45 
  46     return (exx[2] & (1 << 20)) != 0;   /* SSE 4.2 */
  47 }
  48 
  49 /*
  50  * This gets called on the first call. It replaces the function pointer
  51  * so that subsequent calls are routed directly to the chosen implementation.
  52  */
  53 static pg_crc32c
  54 pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len)
  55 {
  56     if (pg_crc32c_sse42_available())
  57         pg_comp_crc32c = pg_comp_crc32c_sse42;
  58     else
  59         pg_comp_crc32c = pg_comp_crc32c_sb8;
  60 
  61     return pg_comp_crc32c(crc, data, len);
  62 }
  63 
  64 pg_crc32c   (*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) = pg_comp_crc32c_choose;
```


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