1  // Copyright 2014 Google LLC
 2  //
 3  // Redistribution and use in source and binary forms, with or without
 4  // modification, are permitted provided that the following conditions are
 5  // met:
 6  //
 7  //     * Redistributions of source code must retain the above copyright
 8  // notice, this list of conditions and the following disclaimer.
 9  //     * Redistributions in binary form must reproduce the above
10  // copyright notice, this list of conditions and the following disclaimer
11  // in the documentation and/or other materials provided with the
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15  // this software without specific prior written permission.
16  //
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20  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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27  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28  
29  #ifdef HAVE_CONFIG_H
30  #include <config.h>  // Must come first
31  #endif
32  
33  #include "common/linux/crc32.h"
34  
35  namespace google_breakpad {
36  
37  // This implementation is based on the sample implementation in RFC 1952.
38  
39  // CRC32 polynomial, in reversed form.
40  // See RFC 1952, or http://en.wikipedia.org/wiki/Cyclic_redundancy_check
41  static const uint32_t kCrc32Polynomial = 0xEDB88320;
42  static uint32_t kCrc32Table[256] = { 0 };
43  
44  #define arraysize(f) (sizeof(f) / sizeof(*f))
45  
46  static void EnsureCrc32TableInited() {
47    if (kCrc32Table[arraysize(kCrc32Table) - 1])
48      return;  // already inited
49    for (uint32_t i = 0; i < arraysize(kCrc32Table); ++i) {
50      uint32_t c = i;
51      for (size_t j = 0; j < 8; ++j) {
52        if (c & 1) {
53          c = kCrc32Polynomial ^ (c >> 1);
54        } else {
55          c >>= 1;
56        }
57      }
58      kCrc32Table[i] = c;
59    }
60  }
61  
62  uint32_t UpdateCrc32(uint32_t start, const void* buf, size_t len) {
63    EnsureCrc32TableInited();
64  
65    uint32_t c = start ^ 0xFFFFFFFF;
66    const uint8_t* u = static_cast<const uint8_t*>(buf);
67    for (size_t i = 0; i < len; ++i) {
68      c = kCrc32Table[(c ^ u[i]) & 0xFF] ^ (c >> 8);
69    }
70    return c ^ 0xFFFFFFFF;
71  }
72  
73  }  // namespace google_breakpad