Subversion Repositories planix.SVN

#include <u.h>
#include <libc.h>
#include <flate.h>

enum
{
        ADLERITERS      = 5552, /* max iters before can overflow 32 bits */
        ADLERBASE       = 65521 /* largest prime smaller than 65536 */
};

ulong
adler32(ulong adler, void *vbuf, int n)
{
        ulong s1, s2;
        uchar *buf, *ebuf;
        int m;

        buf = vbuf;
        s1 = adler & 0xffff;
        s2 = (adler >> 16) & 0xffff;
        for(; n >= 16; n -= m){
                m = n;
                if(m > ADLERITERS)
                        m = ADLERITERS;
                m &= ~15;
                for(ebuf = buf + m; buf < ebuf; buf += 16){
                        s1 += buf[0];
                        s2 += s1;
                        s1 += buf[1];
                        s2 += s1;
                        s1 += buf[2];
                        s2 += s1;
                        s1 += buf[3];
                        s2 += s1;
                        s1 += buf[4];
                        s2 += s1;
                        s1 += buf[5];
                        s2 += s1;
                        s1 += buf[6];
                        s2 += s1;
                        s1 += buf[7];
                        s2 += s1;
                        s1 += buf[8];
                        s2 += s1;
                        s1 += buf[9];
                        s2 += s1;
                        s1 += buf[10];
                        s2 += s1;
                        s1 += buf[11];
                        s2 += s1;
                        s1 += buf[12];
                        s2 += s1;
                        s1 += buf[13];
                        s2 += s1;
                        s1 += buf[14];
                        s2 += s1;
                        s1 += buf[15];
                        s2 += s1;
                }
                s1 %= ADLERBASE;
                s2 %= ADLERBASE;
        }
        if(n){
                for(ebuf = buf + n; buf < ebuf; buf++){
                        s1 += buf[0];
                        s2 += s1;
                }
                s1 %= ADLERBASE;
                s2 %= ADLERBASE;
        }
        return (s2 << 16) + s1;
}