symbian-qemu-0.9.1-12/python-2.6.1/Modules/zlib/adler32.c
changeset 1 2fb8b9db1c86
equal deleted inserted replaced
0:ffa851df0825 1:2fb8b9db1c86
       
     1 /* adler32.c -- 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 /* @(#) $Id$ */
       
     7 
       
     8 #define ZLIB_INTERNAL
       
     9 #include "zlib.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 uLong ZEXPORT adler32(adler, buf, len)
       
    58     uLong adler;
       
    59     const Bytef *buf;
       
    60     uInt len;
       
    61 {
       
    62     unsigned long sum2;
       
    63     unsigned n;
       
    64 
       
    65     /* split Adler-32 into component sums */
       
    66     sum2 = (adler >> 16) & 0xffff;
       
    67     adler &= 0xffff;
       
    68 
       
    69     /* in case user likes doing a byte at a time, keep it fast */
       
    70     if (len == 1) {
       
    71         adler += buf[0];
       
    72         if (adler >= BASE)
       
    73             adler -= BASE;
       
    74         sum2 += adler;
       
    75         if (sum2 >= BASE)
       
    76             sum2 -= BASE;
       
    77         return adler | (sum2 << 16);
       
    78     }
       
    79 
       
    80     /* initial Adler-32 value (deferred check for len == 1 speed) */
       
    81     if (buf == Z_NULL)
       
    82         return 1L;
       
    83 
       
    84     /* in case short lengths are provided, keep it somewhat fast */
       
    85     if (len < 16) {
       
    86         while (len--) {
       
    87             adler += *buf++;
       
    88             sum2 += adler;
       
    89         }
       
    90         if (adler >= BASE)
       
    91             adler -= BASE;
       
    92         MOD4(sum2);             /* only added so many BASE's */
       
    93         return adler | (sum2 << 16);
       
    94     }
       
    95 
       
    96     /* do length NMAX blocks -- requires just one modulo operation */
       
    97     while (len >= NMAX) {
       
    98         len -= NMAX;
       
    99         n = NMAX / 16;          /* NMAX is divisible by 16 */
       
   100         do {
       
   101             DO16(buf);          /* 16 sums unrolled */
       
   102             buf += 16;
       
   103         } while (--n);
       
   104         MOD(adler);
       
   105         MOD(sum2);
       
   106     }
       
   107 
       
   108     /* do remaining bytes (less than NMAX, still just one modulo) */
       
   109     if (len) {                  /* avoid modulos if none remaining */
       
   110         while (len >= 16) {
       
   111             len -= 16;
       
   112             DO16(buf);
       
   113             buf += 16;
       
   114         }
       
   115         while (len--) {
       
   116             adler += *buf++;
       
   117             sum2 += adler;
       
   118         }
       
   119         MOD(adler);
       
   120         MOD(sum2);
       
   121     }
       
   122 
       
   123     /* return recombined sums */
       
   124     return adler | (sum2 << 16);
       
   125 }
       
   126 
       
   127 /* ========================================================================= */
       
   128 uLong ZEXPORT adler32_combine(adler1, adler2, len2)
       
   129     uLong adler1;
       
   130     uLong adler2;
       
   131     z_off_t len2;
       
   132 {
       
   133     unsigned long sum1;
       
   134     unsigned long sum2;
       
   135     unsigned rem;
       
   136 
       
   137     /* the derivation of this formula is left as an exercise for the reader */
       
   138     rem = (unsigned)(len2 % BASE);
       
   139     sum1 = adler1 & 0xffff;
       
   140     sum2 = rem * sum1;
       
   141     MOD(sum2);
       
   142     sum1 += (adler2 & 0xffff) + BASE - 1;
       
   143     sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
       
   144     if (sum1 > BASE) sum1 -= BASE;
       
   145     if (sum1 > BASE) sum1 -= BASE;
       
   146     if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
       
   147     if (sum2 > BASE) sum2 -= BASE;
       
   148     return sum1 | (sum2 << 16);
       
   149 }