关于libmemcached中的crc的实现

2016-12-12 10:15:57来源:作者:IT技术博客大学习人点击

缘起

libmemcached备受青睐,号称错误信息是很详细的,比所谓的memcache模块强多了;但是,就是因为他的名气大,还是被坑了;所谓的错误信息详细在get操作时完全不存在了,不管是连接失败还是各种超时,得到的错误信息都是NOTFOUND;于是乎,我想自己用PHP写一个memcached的client,起初,我可以之实现我需要的几个方法,鉴于memcache的协议很简单,应该是比较容易完成的。

问题

其实,我1天时间已经完成了memcache的几个简单的协议,出于一些不想说的考虑,当add多个server时,我需要把根据key的hash结果和libmemcached中的完全一样;看了libmemcached中几种hash和distribute的策略,我只想选择一种最简单的hash和distribute策略来实现,我选择了 crc32 + modular; 简而言之,算法就是: crc32(key) % count(server) 就Ok了; 但是,问题是PHP的crc32结果和libmemcached中的crc32结果是不同的,鉴于我的C语言水平有限,不想看和看不懂使得我咨询了一下牛人,没有结果,于是还是硬着头皮看吧。

分析

后面分别贴一下libmemcached和php中crc的实现,这里先说结论了:

二者差别不大,主要差别在于:

PHP中的crc32返回的是一个32位的有符号数,而libmemecached中返回的是前者32位有符号数种的高16位,并且忽略了符号位;

如果用PHP实现一个和libmemcached相同的crc32将是:

<?phpecho (crc32('test') >> 16) & 0x7fff;

或者如下实现:

本来只需要简单的位移操作、异或操作就可以处理的事情,用PHP来实现却需要大量的pack、unpack,对‘test’进行crc32大约需要0.1ms(很慢的),如果用上面实现,大约比该实现快100倍

<?phpfunction _crc32($str) {       $arr = array(           0x00000000, 0x77073096, 0xee0e612c, 0x990951ba,           0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,           0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,           0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,           0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,           0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,           0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,           0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5,           0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,           0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,           0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940,           0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,           0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116,           0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,           0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,           0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,           0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a,           0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,           0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818,           0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,           0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,           0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457,           0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c,           0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,           0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,           0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb,           0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,           0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,           0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086,           0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,           0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4,           0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad,           0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,           0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683,           0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,           0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,           0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe,           0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7,           0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,           0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,           0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252,           0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,           0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60,           0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,           0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,           0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f,           0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04,           0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,           0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a,           0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,           0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,           0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21,           0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e,           0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,           0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,           0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,           0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,           0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db,           0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0,           0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,           0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6,           0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf,           0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,           0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d,       );       $table = '';       foreach($arr as $int) {               $table.= pack('N', $int);       }       $crc = pack('N', 4294967295);       for ($i = 0; $i < strlen($str); $i++) {               $m = $crc ^ (chr(0).chr(0).chr(0).$str{$i});               $n = $m & (chr(0).chr(0).chr(0).chr(0xff));               $arr = unpack('N', $n);               $n = $arr[1];               $arr = unpack('N', $crc);               $crc = (pack('N', $arr[1] >> 8)) ^ substr($table, $n*4, 4);       }       $arr = unpack('N', ~$crc);       $res = (pack('N', $arr[1] >> 16)) & (chr(0).chr(0).chr(0x7f).chr(0xff));       $arr = unpack('N', $res);       return $arr[1];}

libmemcached:

static const uint32_tcrc32tab[256] = {   0x00000000, 0x77073096, 0xee0e612c, 0x990951ba,   0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,   0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,   0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,   0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,   0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,   0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,   0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5,   0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,   0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,   0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940,   0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,   0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116,   0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,   0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,   0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,   0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a,   0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,   0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818,   0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,   0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,   0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457,   0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c,   0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,   0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,   0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb,   0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,   0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,   0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086,   0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,   0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4,   0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad,   0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,   0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683,   0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,   0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,   0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe,   0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7,   0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,   0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,   0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252,   0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,   0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60,   0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,   0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,   0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f,   0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04,   0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,   0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a,   0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,   0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,   0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21,   0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e,   0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,   0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,   0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,   0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,   0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db,   0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0,   0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,   0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6,   0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf,   0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,   0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d,};uint32_thash_crc32(const char *key, size_tkey_length){   uint64_t x;   uint32_tcrc = UINT32_MAX;   for (x= 0; x < key_length; x++) {       crc = (crc >> 8) ^ crc32tab[(crc ^ (uint64_t)key[x]) & 0xff];   }   return ((~crc) >> 16) & 0x7fff;}

php中的实现(说明一下: 这里的crc32tab和上面的是一样的):

/* {{{ proto string crc32(string str)  Calculate the crc32 polynomial of a string */PHP_NAMED_FUNCTION(php_if_crc32){   char *p;   int len, nr;   php_uint32crcinit = 0;   register php_uint32crc;   if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "s", &p, &nr) == FAILURE) {       return;   }   crc = crcinit^0xFFFFFFFF;   for (len =+nr; nr--; ++p) {       crc = ((crc >> 8) & 0x00FFFFFF) ^ crc32tab[(crc ^ (*p)) & 0xFF ];   }   RETVAL_LONG(crc^0xFFFFFFFF);}/* }}} */

关于crc32_table 的由来,crc32_table是出于提高效率的目的而诞生的,来源于一个神奇的数字 0x04c11db7:

#include <stdio.h>unsigned long int crc32_table[256]; unsigned long int ulPolynomial = 0x04c11db7; unsigned long int Reflect(unsigned long int ref, char ch) {       unsigned long int value = 0;        // 交换bit0 和bit7,bit1 和bit6,类推       int i;       for(i = 1; i < (ch + 1); i++) {               if(ref & 1)                        value |= 1 << (ch - i);                ref >>= 1;       }        return value; } void init_crc32_table() {       unsigned long int crc,temp;        // 256 个值       int i, j;       for(i = 0; i <= 0xFF; i++) {               temp=Reflect(i, 8);                crc32_table[i]= temp<< 24;                for (j = 0; j < 8; j++){                        unsigned long int t1,t2;                        unsigned long int flag=crc32_table[i]&0x80000000;                        t1=(crc32_table[i] << 1);                        if(flag==0)                                t2=0;                        else                                t2=ulPolynomial;                        crc32_table[i] =t1^t2 ; }                        crc=crc32_table[i];                        crc32_table[i] = Reflect(crc32_table[i], 32);        } }int main(int ac, char ** av) {       init_crc32_table();       int i;       for(i = 0; i < 256; i++) {               printf("0x%08x ", crc32_table[i]);               if (i % 4 == 3) printf(" ");       }       return 0;}

参考资料:

http://baike.baidu.com/view/410181.htm?fr=aladdin

http://hi.baidu.com/qyiyunso/item/c06719c5872ed5d5964452ac

http://zh.wikipedia.org/wiki/CRC32

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