1 #include <u.h> 2 #include <libc.h> 3 #include <flate.h> 4 5 ulong* mkcrctab(ulong poly)6mkcrctab(ulong poly) 7 { 8 ulong *crctab; 9 ulong crc; 10 int i, j; 11 12 crctab = malloc(256 * sizeof(ulong)); 13 if(crctab == nil) 14 return nil; 15 16 for(i = 0; i < 256; i++){ 17 crc = i; 18 for(j = 0; j < 8; j++){ 19 if(crc & 1) 20 crc = (crc >> 1) ^ poly; 21 else 22 crc >>= 1; 23 } 24 crctab[i] = crc; 25 } 26 return crctab; 27 } 28 29 ulong blockcrc(ulong * crctab,ulong crc,void * vbuf,int n)30blockcrc(ulong *crctab, ulong crc, void *vbuf, int n) 31 { 32 uchar *buf, *ebuf; 33 34 crc ^= 0xffffffff; 35 buf = vbuf; 36 ebuf = buf + n; 37 while(buf < ebuf) 38 crc = crctab[(crc & 0xff) ^ *buf++] ^ (crc >> 8); 39 return crc ^ 0xffffffff; 40 } 41