計算CRC32的C模組

#include "string.h"static unsigned int CRC32[256];static int nIsInit = 0;static void init_table(){    int  i = 0, j =0 ;    unsigned int crc;    for(i = 0;i < 256; i++)    {        crc = i;        for(j = 0;j < 8; j++)        {            if(crc & 1)            {                crc = (crc >> 1) ^ 0xEDB88320;            }            else            {                crc = crc >> 1;            }        }        CRC32[i] = crc;    }}unsigned int crc32(unsigned char *buf, int len){    unsigned int ret = 0xFFFFFFFF;    int i = 0;    if( nIsInit != 1 )    {        init_table();        nIsInit = 1;    }    for(i = 0; i < len; i++)    {        ret = CRC32[((ret & 0xFF) ^ buf[i])] ^ (ret >> 8);    }    ret = ~ret;    return ret;}