ref: 6dce09cec3bf6a689fa9a3f838df67d7d48d9d1a
dir: /libflate/adler.c/
#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; }