1 /*

     2  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     3  *

     4  * This code is free software; you can redistribute it and/or modify it

     5  * under the terms of the GNU General Public License version 2 only, as

     6  * published by the Free Software Foundation.  Oracle designates this

     7  * particular file as subject to the "Classpath" exception as provided

     8  * by Oracle in the LICENSE file that accompanied this code.

     9  *

    10  * This code is distributed in the hope that it will be useful, but WITHOUT

    11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    13  * version 2 for more details (a copy is included in the LICENSE file that

    14  * accompanied this code).

    15  *

    16  * You should have received a copy of the GNU General Public License version

    17  * 2 along with this work; if not, write to the Free Software Foundation,

    18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    19  *

    20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    21  * or visit www.oracle.com if you need additional information or have any

    22  * questions.

    23  */

    24 

    25 /* adler32.c -- compute the Adler-32 checksum of a data stream

    26  * Copyright (C) 1995-2011 Mark Adler

    27  * For conditions of distribution and use, see copyright notice in zlib.h

    28  */

    29 

    30 /* @(#) $Id$ */

    31 

    32 #include "zutil.h"

    33 

    34 #define local static

    35 

    36 local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2));

    37 

    38 #define BASE 65521      /* largest prime smaller than 65536 */

    39 #define NMAX 5552

    40 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */

    41 

    42 #define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}

    43 #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);

    44 #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);

    45 #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);

    46 #define DO16(buf)   DO8(buf,0); DO8(buf,8);

    47 

    48 /* use NO_DIVIDE if your processor does not do division in hardware --

    49    try it both ways to see which is faster */

    50 #ifdef NO_DIVIDE

    51 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15

    52    (thank you to John Reiser for pointing this out) */

    53 #  define CHOP(a) \

    54     do { \

    55         unsigned long tmp = a >> 16; \

    56         a &= 0xffffUL; \

    57         a += (tmp << 4) - tmp; \

    58     } while (0)

    59 #  define MOD28(a) \

    60     do { \

    61         CHOP(a); \

    62         if (a >= BASE) a -= BASE; \

    63     } while (0)

    64 #  define MOD(a) \

    65     do { \

    66         CHOP(a); \

    67         MOD28(a); \

    68     } while (0)

    69 #  define MOD63(a) \

    70     do { /* this assumes a is not negative */ \

    71         z_off64_t tmp = a >> 32; \

    72         a &= 0xffffffffL; \

    73         a += (tmp << 8) - (tmp << 5) + tmp; \

    74         tmp = a >> 16; \

    75         a &= 0xffffL; \

    76         a += (tmp << 4) - tmp; \

    77         tmp = a >> 16; \

    78         a &= 0xffffL; \

    79         a += (tmp << 4) - tmp; \

    80         if (a >= BASE) a -= BASE; \

    81     } while (0)

    82 #else

    83 #  define MOD(a) a %= BASE

    84 #  define MOD28(a) a %= BASE

    85 #  define MOD63(a) a %= BASE

    86 #endif

    87 

    88 /* ========================================================================= */

    89 uLong ZEXPORT adler32(adler, buf, len)

    90     uLong adler;

    91     const Bytef *buf;

    92     uInt len;

    93 {

    94     unsigned long sum2;

    95     unsigned n;

    96 

    97     /* split Adler-32 into component sums */

    98     sum2 = (adler >> 16) & 0xffff;

    99     adler &= 0xffff;

   100 

   101     /* in case user likes doing a byte at a time, keep it fast */

   102     if (len == 1) {

   103         adler += buf[0];

   104         if (adler >= BASE)

   105             adler -= BASE;

   106         sum2 += adler;

   107         if (sum2 >= BASE)

   108             sum2 -= BASE;

   109         return adler | (sum2 << 16);

   110     }

   111 

   112     /* initial Adler-32 value (deferred check for len == 1 speed) */

   113     if (buf == Z_NULL)

   114         return 1L;

   115 

   116     /* in case short lengths are provided, keep it somewhat fast */

   117     if (len < 16) {

   118         while (len--) {

   119             adler += *buf++;

   120             sum2 += adler;

   121         }

   122         if (adler >= BASE)

   123             adler -= BASE;

   124         MOD28(sum2);            /* only added so many BASE's */

   125         return adler | (sum2 << 16);

   126     }

   127 

   128     /* do length NMAX blocks -- requires just one modulo operation */

   129     while (len >= NMAX) {

   130         len -= NMAX;

   131         n = NMAX / 16;          /* NMAX is divisible by 16 */

   132         do {

   133             DO16(buf);          /* 16 sums unrolled */

   134             buf += 16;

   135         } while (--n);

   136         MOD(adler);

   137         MOD(sum2);

   138     }

   139 

   140     /* do remaining bytes (less than NMAX, still just one modulo) */

   141     if (len) {                  /* avoid modulos if none remaining */

   142         while (len >= 16) {

   143             len -= 16;

   144             DO16(buf);

   145             buf += 16;

   146         }

   147         while (len--) {

   148             adler += *buf++;

   149             sum2 += adler;

   150         }

   151         MOD(adler);

   152         MOD(sum2);

   153     }

   154 

   155     /* return recombined sums */

   156     return adler | (sum2 << 16);

   157 }

   158 

   159 /* ========================================================================= */

   160 local uLong adler32_combine_(adler1, adler2, len2)

   161     uLong adler1;

   162     uLong adler2;

   163     z_off64_t len2;

   164 {

   165     unsigned long sum1;

   166     unsigned long sum2;

   167     unsigned rem;

   168 

   169     /* for negative len, return invalid adler32 as a clue for debugging */

   170     if (len2 < 0)

   171         return 0xffffffffUL;

   172 

   173     /* the derivation of this formula is left as an exercise for the reader */

   174     MOD63(len2);                /* assumes len2 >= 0 */

   175     rem = (unsigned)len2;

   176     sum1 = adler1 & 0xffff;

   177     sum2 = rem * sum1;

   178     MOD(sum2);

   179     sum1 += (adler2 & 0xffff) + BASE - 1;

   180     sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;

   181     if (sum1 >= BASE) sum1 -= BASE;

   182     if (sum1 >= BASE) sum1 -= BASE;

   183     if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1);

   184     if (sum2 >= BASE) sum2 -= BASE;

   185     return sum1 | (sum2 << 16);

   186 }

   187 

   188 /* ========================================================================= */

   189 uLong ZEXPORT adler32_combine(adler1, adler2, len2)

   190     uLong adler1;

   191     uLong adler2;

   192     z_off_t len2;

   193 {

   194     return adler32_combine_(adler1, adler2, len2);

   195 }

   196 

   197 uLong ZEXPORT adler32_combine64(adler1, adler2, len2)

   198     uLong adler1;

   199     uLong adler2;

   200     z_off64_t len2;

   201 {

   202     return adler32_combine_(adler1, adler2, len2);

   203 }