ref: c11957a7915d355d80ff7e6a21721ba05441ca29
dir: /libflate/crc.c/
#include <u.h> #include <libc.h> #include <flate.h> ulong* mkcrctab(ulong poly) { ulong *crctab; ulong crc; int i, j; crctab = malloc(256 * sizeof(ulong)); if(crctab == nil) return nil; for(i = 0; i < 256; i++){ crc = i; for(j = 0; j < 8; j++){ if(crc & 1) crc = (crc >> 1) ^ poly; else crc >>= 1; } crctab[i] = crc; } return crctab; } ulong blockcrc(ulong *crctab, ulong crc, void *vbuf, int n) { uchar *buf, *ebuf; crc ^= 0xffffffff; buf = vbuf; ebuf = buf + n; while(buf < ebuf) crc = crctab[(crc & 0xff) ^ *buf++] ^ (crc >> 8); return crc ^ 0xffffffff; }