/*
 *	adler32.c -- compute the Adler-32 checksum of a data stream
 *
 *	Copyright (C) 1995--2003 Mark Adler
 *
 * 	Taken from zlib-1.2.1 and adjusted by Robert Spalek.  For conditions of
 * 	distribution and use, see copyright notice in zlib.h.
 */

#include <ucw/lib.h>
#include <ucw/lizard.h>

#define BASE 65521UL	/* largest prime smaller than 65536 */
#define NMAX 5552	/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */

#define DO1(buf,i)  {s1 += buf[i]; s2 += s1;}
#define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
#define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
#define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
#define DO16(buf)   DO8(buf,0); DO8(buf,8);
#define MOD(a) a %= BASE

uint
adler32_update(uint adler, const byte *buf, uint len)
{
  uint s1 = adler & 0xffff;
  uint s2 = (adler >> 16) & 0xffff;
  int k;

  if (!buf) return 1L;

  while (len > 0) {
    k = len < NMAX ? (int)len : NMAX;
    len -= k;
    while (k >= 16) {
      DO16(buf);
      buf += 16;
      k -= 16;
    }
    if (k != 0) do {
      s1 += *buf++;
      s2 += s1;
    } while (--k);
    MOD(s1);
    MOD(s2);
  }
  return (s2 << 16) | s1;
}