/* adler32.c -- compute the Adler-32 checksum of a data stream * Copyright (C) 1995-2003 Mark Adler * For conditions of distribution and use, see copyright notice in zlib.h */ /* @(#) $Id: adler32.c,v 1.1.1.2 2002/03/11 21:53:23 tromey Exp $ */ #define ZLIB_INTERNAL #include "zlib.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); #ifdef NO_DIVIDE # define MOD(a) \ do { \ if (a >= (BASE << 16)) a -= (BASE << 16); \ if (a >= (BASE << 15)) a -= (BASE << 15); \ if (a >= (BASE << 14)) a -= (BASE << 14); \ if (a >= (BASE << 13)) a -= (BASE << 13); \ if (a >= (BASE << 12)) a -= (BASE << 12); \ if (a >= (BASE << 11)) a -= (BASE << 11); \ if (a >= (BASE << 10)) a -= (BASE << 10); \ if (a >= (BASE << 9)) a -= (BASE << 9); \ if (a >= (BASE << 8)) a -= (BASE << 8); \ if (a >= (BASE << 7)) a -= (BASE << 7); \ if (a >= (BASE << 6)) a -= (BASE << 6); \ if (a >= (BASE << 5)) a -= (BASE << 5); \ if (a >= (BASE << 4)) a -= (BASE << 4); \ if (a >= (BASE << 3)) a -= (BASE << 3); \ if (a >= (BASE << 2)) a -= (BASE << 2); \ if (a >= (BASE << 1)) a -= (BASE << 1); \ if (a >= BASE) a -= BASE; \ } while (0) #else # define MOD(a) a %= BASE #endif /* ========================================================================= */ uLong ZEXPORT adler32(adler, buf, len) uLong adler; const Bytef *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 ? (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; }