1ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease/* adler32.c -- compute the Adler-32 checksum of a data stream 2ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease * Copyright (C) 1995-2002 Mark Adler 3ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease * For conditions of distribution and use, see copyright notice in zlib.h 4ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease */ 5ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease 6ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease/* @(#) $Id$ */ 7ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease 8ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease#include "zlib.h" 9ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease 10ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease#define BASE 65521L /* largest prime smaller than 65536 */ 11ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease#define NMAX 5552 12ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ 13ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease 14ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease#define DO1(buf,i) {s1 += buf[i]; s2 += s1;} 15ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease#define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); 16ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease#define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); 17ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease#define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); 18ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease#define DO16(buf) DO8(buf,0); DO8(buf,8); 19ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease 20ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease/* ========================================================================= */ 21ec0bab5697bb31ba980810145f62e3799946ec60Victoria LeaseZEXPORT(uLong) adler32( /* adler, buf, len) */ 22ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease uLong adler, 23ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease const Bytef *buf, 24ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease uInt len ) 25ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease{ 26ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease unsigned long s1 = adler & 0xffff; 27ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease unsigned long s2 = (adler >> 16) & 0xffff; 28ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease int k; 29ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease 30ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease if (buf == Z_NULL) return 1L; 31ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease 32ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease while (len > 0) { 33ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease k = len < NMAX ? len : NMAX; 34ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease len -= k; 35ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease while (k >= 16) { 36ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease DO16(buf); 37ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease buf += 16; 38ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease k -= 16; 39ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease } 40ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease if (k != 0) do { 41ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease s1 += *buf++; 42ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease s2 += s1; 43ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease } while (--k); 44ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease s1 %= BASE; 45ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease s2 %= BASE; 46ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease } 47ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease return (s2 << 16) | s1; 48ec0bab5697bb31ba980810145f62e3799946ec60Victoria Lease} 49