1 /* 2 * libjingle 3 * Copyright 2012, Google, Inc. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions are met: 7 * 8 * 1. Redistributions of source code must retain the above copyright notice, 9 * this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright notice, 11 * this list of conditions and the following disclaimer in the documentation 12 * and/or other materials provided with the distribution. 13 * 3. The name of the author may not be used to endorse or promote products 14 * derived from this software without specific prior written permission. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED 17 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 18 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO 19 * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 20 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 21 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; 22 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 23 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 24 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 25 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28 #include "talk/base/crc32.h" 29 30 #include "talk/base/basicdefs.h" 31 32 namespace talk_base { 33 34 // This implementation is based on the sample implementation in RFC 1952. 35 36 // CRC32 polynomial, in reversed form. 37 // See RFC 1952, or http://en.wikipedia.org/wiki/Cyclic_redundancy_check 38 static const uint32 kCrc32Polynomial = 0xEDB88320; 39 static uint32 kCrc32Table[256] = { 0 }; 40 41 static void EnsureCrc32TableInited() { 42 if (kCrc32Table[ARRAY_SIZE(kCrc32Table) - 1]) 43 return; // already inited 44 for (uint32 i = 0; i < ARRAY_SIZE(kCrc32Table); ++i) { 45 uint32 c = i; 46 for (size_t j = 0; j < 8; ++j) { 47 if (c & 1) { 48 c = kCrc32Polynomial ^ (c >> 1); 49 } else { 50 c >>= 1; 51 } 52 } 53 kCrc32Table[i] = c; 54 } 55 } 56 57 uint32 UpdateCrc32(uint32 start, const void* buf, size_t len) { 58 EnsureCrc32TableInited(); 59 60 uint32 c = start ^ 0xFFFFFFFF; 61 const uint8* u = static_cast<const uint8*>(buf); 62 for (size_t i = 0; i < len; ++i) { 63 c = kCrc32Table[(c ^ u[i]) & 0xFF] ^ (c >> 8); 64 } 65 return c ^ 0xFFFFFFFF; 66 } 67 68 } // namespace talk_base 69 70
