Geant4: adler32.cc Source File

00001 /* adler32.c -- compute the Adler-32 checksum of a data stream
00002  * Copyright (C) 1995-2003 Mark Adler
00003  * For conditions of distribution and use, see copyright notice in zlib.h
00004  */
00005 
00006 /* @(#) $Id: adler32.cc,v 1.1 2005-05-12 21:04:53 duns Exp $ */
00007 
00008 #define ZLIB_INTERNAL
00009 #include "zlib.h"
00010 
00011 #define BASE 65521UL    /* largest prime smaller than 65536 */
00012 #define NMAX 5552
00013 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
00014 
00015 #define DO1(buf,i)  {s1 += buf[i]; s2 += s1;}
00016 #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
00017 #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
00018 #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
00019 #define DO16(buf)   DO8(buf,0); DO8(buf,8);
00020 
00021 #ifdef NO_DIVIDE
00022 #  define MOD(a) \
00023     do { \
00024         if (a >= (BASE << 16)) a -= (BASE << 16); \
00025         if (a >= (BASE << 15)) a -= (BASE << 15); \
00026         if (a >= (BASE << 14)) a -= (BASE << 14); \
00027         if (a >= (BASE << 13)) a -= (BASE << 13); \
00028         if (a >= (BASE << 12)) a -= (BASE << 12); \
00029         if (a >= (BASE << 11)) a -= (BASE << 11); \
00030         if (a >= (BASE << 10)) a -= (BASE << 10); \
00031         if (a >= (BASE << 9)) a -= (BASE << 9); \
00032         if (a >= (BASE << 8)) a -= (BASE << 8); \
00033         if (a >= (BASE << 7)) a -= (BASE << 7); \
00034         if (a >= (BASE << 6)) a -= (BASE << 6); \
00035         if (a >= (BASE << 5)) a -= (BASE << 5); \
00036         if (a >= (BASE << 4)) a -= (BASE << 4); \
00037         if (a >= (BASE << 3)) a -= (BASE << 3); \
00038         if (a >= (BASE << 2)) a -= (BASE << 2); \
00039         if (a >= (BASE << 1)) a -= (BASE << 1); \
00040         if (a >= BASE) a -= BASE; \
00041     } while (0)
00042 #else
00043 #  define MOD(a) a %= BASE
00044 #endif
00045 
00046 /* ========================================================================= */
00047 uLong ZEXPORT adler32(uLong adler, const Bytef *buf, uInt len)
00048 {
00049     unsigned long s1 = adler & 0xffff;
00050     unsigned long s2 = (adler >> 16) & 0xffff;
00051     int k;
00052 
00053     if (buf == Z_NULL) return 1L;
00054 
00055     while (len > 0) {
00056         k = len < NMAX ? (int)len : NMAX;
00057         len -= k;
00058         while (k >= 16) {
00059             DO16(buf);
00060             buf += 16;
00061             k -= 16;
00062         }
00063         if (k != 0) do {
00064             s1 += *buf++;
00065             s2 += s1;
00066         } while (--k);
00067         MOD(s1);
00068         MOD(s2);
00069     }
00070     return (s2 << 16) | s1;
00071 }