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| 1 /* | 1 /* | 
| 2  *  Copyright 2012 The WebRTC Project Authors. All rights reserved. | 2  *  Copyright 2012 The WebRTC Project Authors. All rights reserved. | 
| 3  * | 3  * | 
| 4  *  Use of this source code is governed by a BSD-style license | 4  *  Use of this source code is governed by a BSD-style license | 
| 5  *  that can be found in the LICENSE file in the root of the source | 5  *  that can be found in the LICENSE file in the root of the source | 
| 6  *  tree. An additional intellectual property rights grant can be found | 6  *  tree. An additional intellectual property rights grant can be found | 
| 7  *  in the file PATENTS.  All contributing project authors may | 7  *  in the file PATENTS.  All contributing project authors may | 
| 8  *  be found in the AUTHORS file in the root of the source tree. | 8  *  be found in the AUTHORS file in the root of the source tree. | 
| 9  */ | 9  */ | 
| 10 | 10 | 
| 11 #include "webrtc/base/crc32.h" | 11 #include "webrtc/base/crc32.h" | 
| 12 | 12 | 
| 13 #include "webrtc/base/basicdefs.h" | 13 #include "webrtc/base/basicdefs.h" | 
| 14 | 14 | 
| 15 namespace rtc { | 15 namespace rtc { | 
| 16 | 16 | 
| 17 // This implementation is based on the sample implementation in RFC 1952. | 17 // This implementation is based on the sample implementation in RFC 1952. | 
| 18 | 18 | 
| 19 // CRC32 polynomial, in reversed form. | 19 // CRC32 polynomial, in reversed form. | 
| 20 // See RFC 1952, or http://en.wikipedia.org/wiki/Cyclic_redundancy_check | 20 // See RFC 1952, or http://en.wikipedia.org/wiki/Cyclic_redundancy_check | 
| 21 static const uint32 kCrc32Polynomial = 0xEDB88320; | 21 static const uint32_t kCrc32Polynomial = 0xEDB88320; | 
| 22 static uint32 kCrc32Table[256] = { 0 }; | 22 static uint32_t kCrc32Table[256] = {0}; | 
| 23 | 23 | 
| 24 static void EnsureCrc32TableInited() { | 24 static void EnsureCrc32TableInited() { | 
| 25   if (kCrc32Table[ARRAY_SIZE(kCrc32Table) - 1]) | 25   if (kCrc32Table[ARRAY_SIZE(kCrc32Table) - 1]) | 
| 26     return;  // already inited | 26     return;  // already inited | 
| 27   for (uint32 i = 0; i < ARRAY_SIZE(kCrc32Table); ++i) { | 27   for (uint32_t i = 0; i < ARRAY_SIZE(kCrc32Table); ++i) { | 
| 28     uint32 c = i; | 28     uint32_t c = i; | 
| 29     for (size_t j = 0; j < 8; ++j) { | 29     for (size_t j = 0; j < 8; ++j) { | 
| 30       if (c & 1) { | 30       if (c & 1) { | 
| 31         c = kCrc32Polynomial ^ (c >> 1); | 31         c = kCrc32Polynomial ^ (c >> 1); | 
| 32       } else { | 32       } else { | 
| 33         c >>= 1; | 33         c >>= 1; | 
| 34       } | 34       } | 
| 35     } | 35     } | 
| 36     kCrc32Table[i] = c; | 36     kCrc32Table[i] = c; | 
| 37   } | 37   } | 
| 38 } | 38 } | 
| 39 | 39 | 
| 40 uint32 UpdateCrc32(uint32 start, const void* buf, size_t len) { | 40 uint32_t UpdateCrc32(uint32_t start, const void* buf, size_t len) { | 
| 41   EnsureCrc32TableInited(); | 41   EnsureCrc32TableInited(); | 
| 42 | 42 | 
| 43   uint32 c = start ^ 0xFFFFFFFF; | 43   uint32_t c = start ^ 0xFFFFFFFF; | 
| 44   const uint8* u = static_cast<const uint8*>(buf); | 44   const uint8_t* u = static_cast<const uint8_t*>(buf); | 
| 45   for (size_t i = 0; i < len; ++i) { | 45   for (size_t i = 0; i < len; ++i) { | 
| 46     c = kCrc32Table[(c ^ u[i]) & 0xFF] ^ (c >> 8); | 46     c = kCrc32Table[(c ^ u[i]) & 0xFF] ^ (c >> 8); | 
| 47   } | 47   } | 
| 48   return c ^ 0xFFFFFFFF; | 48   return c ^ 0xFFFFFFFF; | 
| 49 } | 49 } | 
| 50 | 50 | 
| 51 }  // namespace rtc | 51 }  // namespace rtc | 
| 52 | 52 | 
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