support/adler32.c

   1 /* adler32.c -- compute the Adler-32 checksum of a data stream
   2  * Copyright (C) 1995-2006 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 local static
  12
  13 #ifdef _LARGEFILE64_SOURCE
  14    local uLong adler32_combine_(uLong adler1, uLong adler2, off64_t len2);
  15 #else
  16    local uLong adler32_combine_(uLong adler1, uLong adler2, z_off_t len2);
  17 #endif
  18
  19
  20 #define BASE 65521UL    /* largest prime smaller than 65536 */
  21 #define NMAX 5552
  22 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
  23
  24 #define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}
  25 #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
  26 #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
  27 #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
  28 #define DO16(buf)   DO8(buf,0); DO8(buf,8);
  29
  30 /* use NO_DIVIDE if your processor does not do division in hardware */
  31 #ifdef NO_DIVIDE
  32 #  define MOD(a) \
  33     do { \
  34         if (a >= (BASE << 16)) a -= (BASE << 16); \
  35         if (a >= (BASE << 15)) a -= (BASE << 15); \
  36         if (a >= (BASE << 14)) a -= (BASE << 14); \
  37         if (a >= (BASE << 13)) a -= (BASE << 13); \
  38         if (a >= (BASE << 12)) a -= (BASE << 12); \
  39         if (a >= (BASE << 11)) a -= (BASE << 11); \
  40         if (a >= (BASE << 10)) a -= (BASE << 10); \
  41         if (a >= (BASE << 9)) a -= (BASE << 9); \
  42         if (a >= (BASE << 8)) a -= (BASE << 8); \
  43         if (a >= (BASE << 7)) a -= (BASE << 7); \
  44         if (a >= (BASE << 6)) a -= (BASE << 6); \
  45         if (a >= (BASE << 5)) a -= (BASE << 5); \
  46         if (a >= (BASE << 4)) a -= (BASE << 4); \
  47         if (a >= (BASE << 3)) a -= (BASE << 3); \
  48         if (a >= (BASE << 2)) a -= (BASE << 2); \
  49         if (a >= (BASE << 1)) a -= (BASE << 1); \
  50         if (a >= BASE) a -= BASE; \
  51     } while (0)
  52 #  define MOD4(a) \
  53     do { \
  54         if (a >= (BASE << 4)) a -= (BASE << 4); \
  55         if (a >= (BASE << 3)) a -= (BASE << 3); \
  56         if (a >= (BASE << 2)) a -= (BASE << 2); \
  57         if (a >= (BASE << 1)) a -= (BASE << 1); \
  58         if (a >= BASE) a -= BASE; \
  59     } while (0)
  60 #else
  61 #  define MOD(a) a %= BASE
  62 #  define MOD4(a) a %= BASE
  63 #endif
  64
  65 /* ========================================================================= */
  66 uLong ZEXPORT adler32(adler, buf, len)
  67     uLong adler;
  68     const Bytef *buf;
  69     uInt len;
  70 {
  71     unsigned long sum2;
  72     unsigned n;
  73
  74     /* split Adler-32 into component sums */
  75     sum2 = (adler >> 16) & 0xffff;
  76     adler &= 0xffff;
  77
  78     /* in case user likes doing a byte at a time, keep it fast */
  79     if (len == 1) {
  80         adler += buf[0];
  81         if (adler >= BASE)
  82             adler -= BASE;
  83         sum2 += adler;
  84         if (sum2 >= BASE)
  85             sum2 -= BASE;
  86         return adler | (sum2 << 16);
  87     }
  88
  89     /* initial Adler-32 value (deferred check for len == 1 speed) */
  90     if (buf == Z_NULL)
  91         return 1L;
  92
  93     /* in case short lengths are provided, keep it somewhat fast */
  94     if (len < 16) {
  95         while (len--) {
  96             adler += *buf++;
  97             sum2 += adler;
  98         }
  99         if (adler >= BASE)
 100             adler -= BASE;
 101         MOD4(sum2);             /* only added so many BASE's */
 102         return adler | (sum2 << 16);
 103     }
 104
 105     /* do length NMAX blocks -- requires just one modulo operation */
 106     while (len >= NMAX) {
 107         len -= NMAX;
 108         n = NMAX / 16;          /* NMAX is divisible by 16 */
 109         do {
 110             DO16(buf);          /* 16 sums unrolled */
 111             buf += 16;
 112         } while (--n);
 113         MOD(adler);
 114         MOD(sum2);
 115     }
 116
 117     /* do remaining bytes (less than NMAX, still just one modulo) */
 118     if (len) {                  /* avoid modulos if none remaining */
 119         while (len >= 16) {
 120             len -= 16;
 121             DO16(buf);
 122             buf += 16;
 123         }
 124         while (len--) {
 125             adler += *buf++;
 126             sum2 += adler;
 127         }
 128         MOD(adler);
 129         MOD(sum2);
 130     }
 131
 132     /* return recombined sums */
 133     return adler | (sum2 << 16);
 134 }
 135
 136 /* ========================================================================= */
 137 local uLong adler32_combine_(adler1, adler2, len2)
 138     uLong adler1;
 139     uLong adler2;
 140 #ifdef _LARGEFILE64_SOURCE
 141     off64_t len2;
 142 #else
 143     z_off_t len2;
 144 #endif
 145 {
 146     unsigned long sum1;
 147     unsigned long sum2;
 148     unsigned rem;
 149
 150     /* the derivation of this formula is left as an exercise for the reader */
 151     rem = (unsigned)(len2 % BASE);
 152     sum1 = adler1 & 0xffff;
 153     sum2 = rem * sum1;
 154     MOD(sum2);
 155     sum1 += (adler2 & 0xffff) + BASE - 1;
 156     sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
 157     if (sum1 > BASE) sum1 -= BASE;
 158     if (sum1 > BASE) sum1 -= BASE;
 159     if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
 160     if (sum2 > BASE) sum2 -= BASE;
 161     return sum1 | (sum2 << 16);
 162 }
 163
 164 /* ========================================================================= */
 165 uLong ZEXPORT adler32_combine(adler1, adler2, len2)
 166     uLong adler1;
 167     uLong adler2;
 168     z_off_t len2;
 169 {
 170     return adler32_combine_(adler1, adler2, len2);
 171 }
 172
 173 #ifdef _LARGEFILE64_SOURCE
 174 uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
 175     uLong adler1;
 176     uLong adler2;
 177     off64_t len2;
 178 {
 179     return adler32_combine_(adler1, adler2, len2);
 180 }
 181 #else
 182 uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
 183     uLong adler1;
 184     uLong adler2;
 185     z_off_t len2;
 186 {
 187     return adler32_combine_(adler1, adler2, len2);
 188 }
 189 #endif