/* adler32.c -- compute the Adler-32 checksum of a data stream * Copyright (C) 1995 Mark Adler * For conditions of distribution and use, see copyright notice in zlib.h */ /* $Id: adler32.c,v 1.5 1995/04/14 14:49:51 jloup Exp $ */ #include "zutil.h" #define BASE 65521 /* 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) {s1 += *buf++; s2 += s1;} #define DO2(buf) DO1(buf); DO1(buf); #define DO4(buf) DO2(buf); DO2(buf); #define DO8(buf) DO4(buf); DO4(buf); #define DO16(buf) DO8(buf); DO8(buf); /* ========================================================================= */ uLong adler32(adler, buf, len) uLong adler; Byte *buf; uInt len; { unsigned long s1 = adler & 0xffff; unsigned long s2 = (adler >> 16) & 0xffff; int k; if (buf == Z_NULL) return 1L; while (len > 0) { k = len < NMAX ? len : NMAX; len -= k; while (k >= 16) { DO16(buf); k -= 16; } if (k != 0) do { DO1(buf); } while (--k); s1 %= BASE; s2 %= BASE; } return (s2 << 16) | s1; }