Subversion Repositories planix.SVN

#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;
}