01-CRC16实现参考

附录C CRC16实现参考

Redis集群使用CRC16对键名进行散列计算来确定键与slot的对应关系，其ANSI C的实现如下附代码，开发支持Cluster特性的客户端时可以以此为参考。该代码摘自Redis官方网站（http://redis.io）。

/* * Copyright 2001-2010 Georges Menie (www.menie.org) * Copyright 2010 Salvatore Sanfilippo (adapted to Redis coding style) * All rights reserved. * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are met: * *　　 * Redistributions of source code must retain the above copyright *　　 notice, this list of conditions and the following disclaimer. *　　 * Redistributions in binary form must reproduce the above copyright *　　 notice, this list of conditions and the following disclaimer in the *　　 documentation and/or other materials provided with the distribution. *　　 * Neither the name of the University of California, Berkeley nor the *　　 names of its contributors may be used to endorse or promote products *　　 derived from this software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND ANY * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL THE REGENTS AND CONTRIBUTORS BE LIABLE FOR ANY * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ /* CRC16 implementation according to CCITT standards. * * Note by @antirez: this is actually the XMODEM CRC 16 algorithm, using the * following parameters: * * Name　　　　　　　　　　 : "XMODEM", also known as "ZMODEM", "CRC-16/ACORN" * Width　　　　　　　　　　 : 16 bit * Poly　　　　　　　　　　 : 1021 (That is actually x^16 + x^12 + x^5 + 1) * Initialization　　　　　　 : 0000 * Reflect Input byte　　　　 : False * Reflect Output CRC　　　　 : False * Xor constant to output CRC : 0000 * Output for "123456789"　　 : 31C3 */ 

static const uint16_t crc16tab[256]= {
　　0x0000,0x1021,0x2042,0x3063,0x4084,0x50a5,0x60c6,0x70e7,
　　0x8108,0x9129,0xa14a,0xb16b,0xc18c,0xd1ad,0xe1ce,0xf1ef,
　　0x1231,0x0210,0x3273,0x2252,0x52b5,0x4294,0x72f7,0x62d6,
　　0x9339,0x8318,0xb37b,0xa35a,0xd3bd,0xc39c,0xf3ff,0xe3de,
　　0x2462,0x3443,0x0420,0x1401,0x64e6,0x74c7,0x44a4,0x5485,
　　0xa56a,0xb54b,0x8528,0x9509,0xe5ee,0xf5cf,0xc5ac,0xd58d,
　　0x3653,0x2672,0x1611,0x0630,0x76d7,0x66f6,0x5695,0x46b4,
　　0xb75b,0xa77a,0x9719,0x8738,0xf7df,0xe7fe,0xd79d,0xc7bc,
　　0x48c4,0x58e5,0x6886,0x78a7,0x0840,0x1861,0x2802,0x3823,
　　0xc9cc,0xd9ed,0xe98e,0xf9af,0x8948,0x9969,0xa90a,0xb92b,
　　0x5af5,0x4ad4,0x7ab7,0x6a96,0x1a71,0x0a50,0x3a33,0x2a12,
　　0xdbfd,0xcbdc,0xfbbf,0xeb9e,0x9b79,0x8b58,0xbb3b,0xab1a,
　　0x6ca6,0x7c87,0x4ce4,0x5cc5,0x2c22,0x3c03,0x0c60,0x1c41,
　　0xedae,0xfd8f,0xcdec,0xddcd,0xad2a,0xbd0b,0x8d68,0x9d49,
　　0x7e97,0x6eb6,0x5ed5,0x4ef4,0x3e13,0x2e32,0x1e51,0x0e70,
　　0xff9f,0xefbe,0xdfdd,0xcffc,0xbf1b,0xaf3a,0x9f59,0x8f78,
　　0x9188,0x81a9,0xb1ca,0xa1eb,0xd10c,0xc12d,0xf14e,0xe16f,
　　0x1080,0x00a1,0x30c2,0x20e3,0x5004,0x4025,0x7046,0x6067,
　　0x83b9,0x9398,0xa3fb,0xb3da,0xc33d,0xd31c,0xe37f,0xf35e,
　　0x02b1,0x1290,0x22f3,0x32d2,0x4235,0x5214,0x6277,0x7256,
　　0xb5ea,0xa5cb,0x95a8,0x8589,0xf56e,0xe54f,0xd52c,0xc50d,
　　0x34e2,0x24c3,0x14a0,0x0481,0x7466,0x6447,0x5424,0x4405,
　　0xa7db,0xb7fa,0x8799,0x97b8,0xe75f,0xf77e,0xc71d,0xd73c,
　　0x26d3,0x36f2,0x0691,0x16b0,0x6657,0x7676,0x4615,0x5634,
　　0xd94c,0xc96d,0xf90e,0xe92f,0x99c8,0x89e9,0xb98a,0xa9ab,
　　0x5844,0x4865,0x7806,0x6827,0x18c0,0x08e1,0x3882,0x28a3,
　　0xcb7d,0xdb5c,0xeb3f,0xfb1e,0x8bf9,0x9bd8,0xabbb,0xbb9a,
　　0x4a75,0x5a54,0x6a37,0x7a16,0x0af1,0x1ad0,0x2ab3,0x3a92,
　　0xfd2e,0xed0f,0xdd6c,0xcd4d,0xbdaa,0xad8b,0x9de8,0x8dc9,
　　0x7c26,0x6c07,0x5c64,0x4c45,0x3ca2,0x2c83,0x1ce0,0x0cc1,
　　0xef1f,0xff3e,0xcf5d,0xdf7c,0xaf9b,0xbfba,0x8fd9,0x9ff8,
　　0x6e17,0x7e36,0x4e55,0x5e74,0x2e93,0x3eb2,0x0ed1,0x1ef0
};
uint16_t crc16(const char *buf, int len) {
　　int counter;
　　uint16_t crc = 0;
　　for (counter = 0; counter < len; counter++)
　　　　　　crc = (crc<>8) ^ *buf++)&0x00FF];
　　return crc;
}