adler32.c revision 33908
1218885Sdim/* adler32.c -- compute the Adler-32 checksum of a data stream 2218885Sdim * Copyright (C) 1995-1998 Mark Adler 3218885Sdim * For conditions of distribution and use, see copyright notice in zlib.h 4218885Sdim */ 5218885Sdim 6218885Sdim/* $FreeBSD: head/lib/libz/adler32.c 33908 1998-02-28 06:08:17Z steve $ */ 7218885Sdim 8218885Sdim#include "zlib.h" 9218885Sdim 10218885Sdim#define BASE 65521L /* largest prime smaller than 65536 */ 11218885Sdim#define NMAX 5552 12218885Sdim/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ 13218885Sdim 14218885Sdim#define DO1(buf,i) {s1 += buf[i]; s2 += s1;} 15218885Sdim#define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); 16218885Sdim#define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); 17218885Sdim#define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); 18218885Sdim#define DO16(buf) DO8(buf,0); DO8(buf,8); 19218885Sdim 20218885Sdim/* ========================================================================= */ 21218885SdimuLong ZEXPORT adler32(adler, buf, len) 22218885Sdim uLong adler; 23218885Sdim const Bytef *buf; 24218885Sdim uInt len; 25221345Sdim{ 26218885Sdim unsigned long s1 = adler & 0xffff; 27218885Sdim unsigned long s2 = (adler >> 16) & 0xffff; 28218885Sdim int k; 29218885Sdim 30218885Sdim if (buf == Z_NULL) return 1L; 31218885Sdim 32218885Sdim while (len > 0) { 33218885Sdim k = len < NMAX ? len : NMAX; 34218885Sdim len -= k; 35218885Sdim while (k >= 16) { 36218885Sdim DO16(buf); 37218885Sdim buf += 16; 38218885Sdim k -= 16; 39218885Sdim } 40218885Sdim if (k != 0) do { 41218885Sdim s1 += *buf++; 42218885Sdim s2 += s1; 43218885Sdim } while (--k); 44218885Sdim s1 %= BASE; 45218885Sdim s2 %= BASE; 46218885Sdim } 47218885Sdim return (s2 << 16) | s1; 48218885Sdim} 49218885Sdim