libkern/zlib/adler32.c

   1 /*
   2  * Copyright (c) 2008 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. The rights granted to you under the License
  10  * may not be used to create, or enable the creation or redistribution of,
  11  * unlawful or unlicensed copies of an Apple operating system, or to
  12  * circumvent, violate, or enable the circumvention or violation of, any
  13  * terms of an Apple operating system software license agreement.
  14  *
  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
  19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  21  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  23  * Please see the License for the specific language governing rights and
  24  * limitations under the License.
  25  *
  26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  27  */
  28 /* adler32.c -- compute the Adler-32 checksum of a data stream
  29  * Copyright (C) 1995-2004 Mark Adler
  30  * For conditions of distribution and use, see copyright notice in zlib.h
  31  */
  32
  33 /* @(#) $Id$ */
  34
  35 #define ZLIB_INTERNAL
  36 #if KERNEL
  37     #include <libkern/zlib.h>
  38 #else
  39     #include "zlib.h"
  40 #endif /* KERNEL */
  41
  42 #define BASE 65521UL    /* largest prime smaller than 65536 */
  43 #define NMAX 5552
  44 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
  45
  46 #define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}
  47 #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
  48 #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
  49 #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
  50 #define DO16(buf)   DO8(buf,0); DO8(buf,8);
  51
  52 /* use NO_DIVIDE if your processor does not do division in hardware */
  53 #ifdef NO_DIVIDE
  54 #  define MOD(a) \
  55     do { \
  56         if (a >= (BASE << 16)) a -= (BASE << 16); \
  57         if (a >= (BASE << 15)) a -= (BASE << 15); \
  58         if (a >= (BASE << 14)) a -= (BASE << 14); \
  59         if (a >= (BASE << 13)) a -= (BASE << 13); \
  60         if (a >= (BASE << 12)) a -= (BASE << 12); \
  61         if (a >= (BASE << 11)) a -= (BASE << 11); \
  62         if (a >= (BASE << 10)) a -= (BASE << 10); \
  63         if (a >= (BASE << 9)) a -= (BASE << 9); \
  64         if (a >= (BASE << 8)) a -= (BASE << 8); \
  65         if (a >= (BASE << 7)) a -= (BASE << 7); \
  66         if (a >= (BASE << 6)) a -= (BASE << 6); \
  67         if (a >= (BASE << 5)) a -= (BASE << 5); \
  68         if (a >= (BASE << 4)) a -= (BASE << 4); \
  69         if (a >= (BASE << 3)) a -= (BASE << 3); \
  70         if (a >= (BASE << 2)) a -= (BASE << 2); \
  71         if (a >= (BASE << 1)) a -= (BASE << 1); \
  72         if (a >= BASE) a -= BASE; \
  73     } while (0)
  74 #  define MOD4(a) \
  75     do { \
  76         if (a >= (BASE << 4)) a -= (BASE << 4); \
  77         if (a >= (BASE << 3)) a -= (BASE << 3); \
  78         if (a >= (BASE << 2)) a -= (BASE << 2); \
  79         if (a >= (BASE << 1)) a -= (BASE << 1); \
  80         if (a >= BASE) a -= BASE; \
  81     } while (0)
  82 #else
  83 #  define MOD(a) a %= BASE
  84 #  define MOD4(a) a %= BASE
  85 #endif
  86
  87 /* ========================================================================= */
  88 uLong ZEXPORT adler32(adler, buf, len)
  89     uLong adler;
  90     const Bytef *buf;
  91     uInt len;
  92 {
  93     unsigned long sum2;
  94     unsigned n;
  95
  96     /* split Adler-32 into component sums */
  97     sum2 = (adler >> 16) & 0xffff;
  98     adler &= 0xffff;
  99
 100     /* in case user likes doing a byte at a time, keep it fast */
 101     if (len == 1) {
 102         adler += buf[0];
 103         if (adler >= BASE)
 104             adler -= BASE;
 105         sum2 += adler;
 106         if (sum2 >= BASE)
 107             sum2 -= BASE;
 108         return adler | (sum2 << 16);
 109     }
 110
 111     /* initial Adler-32 value (deferred check for len == 1 speed) */
 112     if (buf == Z_NULL)
 113         return 1L;
 114
 115     /* in case short lengths are provided, keep it somewhat fast */
 116     if (len < 16) {
 117         while (len--) {
 118             adler += *buf++;
 119             sum2 += adler;
 120         }
 121         if (adler >= BASE)
 122             adler -= BASE;
 123         MOD4(sum2);             /* only added so many BASE's */
 124         return adler | (sum2 << 16);
 125     }
 126
 127     /* do length NMAX blocks -- requires just one modulo operation */
 128     while (len >= NMAX) {
 129         len -= NMAX;
 130         n = NMAX / 16;          /* NMAX is divisible by 16 */
 131         do {
 132             DO16(buf);          /* 16 sums unrolled */
 133             buf += 16;
 134         } while (--n);
 135         MOD(adler);
 136         MOD(sum2);
 137     }
 138
 139     /* do remaining bytes (less than NMAX, still just one modulo) */
 140     if (len) {                  /* avoid modulos if none remaining */
 141         while (len >= 16) {
 142             len -= 16;
 143             DO16(buf);
 144             buf += 16;
 145         }
 146         while (len--) {
 147             adler += *buf++;
 148             sum2 += adler;
 149         }
 150         MOD(adler);
 151         MOD(sum2);
 152     }
 153
 154     /* return recombined sums */
 155     return adler | (sum2 << 16);
 156 }
 157
 158 /* ========================================================================= */
 159 uLong ZEXPORT adler32_combine(adler1, adler2, len2)
 160     uLong adler1;
 161     uLong adler2;
 162     z_off_t len2;
 163 {
 164     unsigned long sum1;
 165     unsigned long sum2;
 166     unsigned rem;
 167
 168     /* the derivation of this formula is left as an exercise for the reader */
 169     rem = (unsigned)(len2 % BASE);
 170     sum1 = adler1 & 0xffff;
 171     sum2 = rem * sum1;
 172     MOD(sum2);
 173     sum1 += (adler2 & 0xffff) + BASE - 1;
 174     sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
 175     if (sum1 > BASE) sum1 -= BASE;
 176     if (sum1 > BASE) sum1 -= BASE;
 177     if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
 178     if (sum2 > BASE) sum2 -= BASE;
 179     return sum1 | (sum2 << 16);
 180 }