1 /* adler32.cpp -- compute the Adler-32 checksum of a data stream

     2  * Copyright (C) 1995-2004 Mark Adler

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

     4  */

     5 

     6 /* @(#) $Id: adler32.cpp,v 1.1.2.1 2008/08/14 15:26:57 e0222316 Exp $ */

     7 

     8 #define ZLIB_INTERNAL

     9 #include "libzcore.h"

    10 

    11 #define BASE 65521UL    /* largest prime smaller than 65536 */

    12 #define NMAX 5552

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

    14 

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

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

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

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

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

    20 

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

    22 #ifdef NO_DIVIDE

    23 #  define MOD(a) \

    24     do { \

    25         if (a >= (BASE << 16)) a -= (BASE << 16); \

    26         if (a >= (BASE << 15)) a -= (BASE << 15); \

    27         if (a >= (BASE << 14)) a -= (BASE << 14); \

    28         if (a >= (BASE << 13)) a -= (BASE << 13); \

    29         if (a >= (BASE << 12)) a -= (BASE << 12); \

    30         if (a >= (BASE << 11)) a -= (BASE << 11); \

    31         if (a >= (BASE << 10)) a -= (BASE << 10); \

    32         if (a >= (BASE << 9)) a -= (BASE << 9); \

    33         if (a >= (BASE << 8)) a -= (BASE << 8); \

    34         if (a >= (BASE << 7)) a -= (BASE << 7); \

    35         if (a >= (BASE << 6)) a -= (BASE << 6); \

    36         if (a >= (BASE << 5)) a -= (BASE << 5); \

    37         if (a >= (BASE << 4)) a -= (BASE << 4); \

    38         if (a >= (BASE << 3)) a -= (BASE << 3); \

    39         if (a >= (BASE << 2)) a -= (BASE << 2); \

    40         if (a >= (BASE << 1)) a -= (BASE << 1); \

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

    42     } while (0)

    43 #  define MOD4(a) \

    44     do { \

    45         if (a >= (BASE << 4)) a -= (BASE << 4); \

    46         if (a >= (BASE << 3)) a -= (BASE << 3); \

    47         if (a >= (BASE << 2)) a -= (BASE << 2); \

    48         if (a >= (BASE << 1)) a -= (BASE << 1); \

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

    50     } while (0)

    51 #else

    52 #  define MOD(a) a %= BASE

    53 #  define MOD4(a) a %= BASE

    54 #endif

    55 

    56 /* ========================================================================= */

    57 

    58 

    59 #ifdef __SYMBIAN32__

    60 EXPORT_C uLong  adler32_r(uLong adler,const Bytef *  buf,uInt len)

    61 #else

    62 uLong ZEXPORT adler32(adler, buf, len)

    63     uLong adler;

    64     const Bytef *buf;

    65     uInt len;

    66 #endif /* __SYMBIAN32__ */

    67 {

    68     unsigned long sum2;

    69     unsigned n;

    70 

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

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

    73     adler &= 0xffff;

    74 

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

    76     if (len == 1) {

    77         adler += buf[0];

    78         if (adler >= BASE)

    79             adler -= BASE;

    80         sum2 += adler;

    81         if (sum2 >= BASE)

    82             sum2 -= BASE;

    83         return adler | (sum2 << 16);

    84     }

    85 

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

    87     if (buf == Z_NULL)

    88         return 1L;

    89 

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

    91     if (len < 16) {

    92         while (len--) {

    93             adler += *buf++;

    94             sum2 += adler;

    95         }

    96         if (adler >= BASE)

    97             adler -= BASE;

    98         MOD4(sum2);             /* only added so many BASE's */

    99         return adler | (sum2 << 16);

   100     }

   101 

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

   103     while (len >= NMAX) {

   104         len -= NMAX;

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

   106         do {

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

   108             buf += 16;

   109         } while (--n);

   110         MOD(adler);

   111         MOD(sum2);

   112     }

   113 

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

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

   116         while (len >= 16) {

   117             len -= 16;

   118             DO16(buf);

   119             buf += 16;

   120         }

   121         while (len--) {

   122             adler += *buf++;

   123             sum2 += adler;

   124         }

   125         MOD(adler);

   126         MOD(sum2);

   127     }

   128 

   129     /* return recombined sums */

   130     return adler | (sum2 << 16);

   131 }

   132 

   133 /* ========================================================================= */

   134 

   135 #ifdef __SYMBIAN32__

   136 EXPORT_C uLong adler32_combine_r(uLong adler1, uLong adler2, z_off_t len2)

   137 #else

   138 uLong ZEXPORT adler32_combine(adler1, adler2, len2)

   139     uLong adler1;

   140     uLong adler2;

   141     z_off_t len2;

   142 #endif /* __SYMBIAN32__ */

   143 {

   144     unsigned long sum1;

   145     unsigned long sum2;

   146     unsigned rem;

   147 

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

   149     rem = (unsigned)(len2 % BASE);

   150     sum1 = adler1 & 0xffff;

   151     sum2 = rem * sum1;

   152     MOD(sum2);

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

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

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

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

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

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

   159     return sum1 | (sum2 << 16);

   160 }