lib/libz/adler32.c

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This source file includes following definitions.
adler32
adler32_combine
    1 /*      $OpenBSD: adler32.c,v 1.9 2006/07/20 11:14:10 mickey Exp $      */
    2 /* adler32.c -- compute the Adler-32 checksum of a data stream
    3  * Copyright (C) 1995-2004 Mark Adler
    4  * For conditions of distribution and use, see copyright notice in zlib.h
    5  */
    6 
    7 #define ZLIB_INTERNAL
    8 #include "zlib.h"
    9 
   10 #define BASE 65521UL    /* largest prime smaller than 65536 */
   11 #define NMAX 5552
   12 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
   13 
   14 #define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}
   15 #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
   16 #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
   17 #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
   18 #define DO16(buf)   DO8(buf,0); DO8(buf,8);
   19 
   20 /* use NO_DIVIDE if your processor does not do division in hardware */
   21 #ifdef NO_DIVIDE
   22 #  define MOD(a) \
   23     do { \
   24         if (a >= (BASE << 16)) a -= (BASE << 16); \
   25         if (a >= (BASE << 15)) a -= (BASE << 15); \
   26         if (a >= (BASE << 14)) a -= (BASE << 14); \
   27         if (a >= (BASE << 13)) a -= (BASE << 13); \
   28         if (a >= (BASE << 12)) a -= (BASE << 12); \
   29         if (a >= (BASE << 11)) a -= (BASE << 11); \
   30         if (a >= (BASE << 10)) a -= (BASE << 10); \
   31         if (a >= (BASE << 9)) a -= (BASE << 9); \
   32         if (a >= (BASE << 8)) a -= (BASE << 8); \
   33         if (a >= (BASE << 7)) a -= (BASE << 7); \
   34         if (a >= (BASE << 6)) a -= (BASE << 6); \
   35         if (a >= (BASE << 5)) a -= (BASE << 5); \
   36         if (a >= (BASE << 4)) a -= (BASE << 4); \
   37         if (a >= (BASE << 3)) a -= (BASE << 3); \
   38         if (a >= (BASE << 2)) a -= (BASE << 2); \
   39         if (a >= (BASE << 1)) a -= (BASE << 1); \
   40         if (a >= BASE) a -= BASE; \
   41     } while (0)
   42 #  define MOD4(a) \
   43     do { \
   44         if (a >= (BASE << 4)) a -= (BASE << 4); \
   45         if (a >= (BASE << 3)) a -= (BASE << 3); \
   46         if (a >= (BASE << 2)) a -= (BASE << 2); \
   47         if (a >= (BASE << 1)) a -= (BASE << 1); \
   48         if (a >= BASE) a -= BASE; \
   49     } while (0)
   50 #else
   51 #  define MOD(a) a %= BASE
   52 #  define MOD4(a) a %= BASE
   53 #endif
   54 
   55 /* ========================================================================= */
   56 uLong ZEXPORT adler32(adler, buf, len)
   57     uLong adler;
   58     const Bytef *buf;
   59     uInt len;
   60 {
   61     unsigned long sum2;
   62     unsigned n;
   63 
   64     /* split Adler-32 into component sums */
   65     sum2 = (adler >> 16) & 0xffff;
   66     adler &= 0xffff;
   67 
   68     /* in case user likes doing a byte at a time, keep it fast */
   69     if (len == 1) {
   70         adler += buf[0];
   71         if (adler >= BASE)
   72             adler -= BASE;
   73         sum2 += adler;
   74         if (sum2 >= BASE)
   75             sum2 -= BASE;
   76         return adler | (sum2 << 16);
   77     }
   78 
   79     /* initial Adler-32 value (deferred check for len == 1 speed) */
   80     if (buf == Z_NULL)
   81         return 1L;
   82 
   83     /* in case short lengths are provided, keep it somewhat fast */
   84     if (len < 16) {
   85         while (len--) {
   86             adler += *buf++;
   87             sum2 += adler;
   88         }
   89         if (adler >= BASE)
   90             adler -= BASE;
   91         MOD4(sum2);             /* only added so many BASE's */
   92         return adler | (sum2 << 16);
   93     }
   94 
   95     /* do length NMAX blocks -- requires just one modulo operation */
   96     while (len >= NMAX) {
   97         len -= NMAX;
   98         n = NMAX / 16;          /* NMAX is divisible by 16 */
   99         do {
  100             DO16(buf);          /* 16 sums unrolled */
  101             buf += 16;
  102         } while (--n);
  103         MOD(adler);
  104         MOD(sum2);
  105     }
  106 
  107     /* do remaining bytes (less than NMAX, still just one modulo) */
  108     if (len) {                  /* avoid modulos if none remaining */
  109         while (len >= 16) {
  110             len -= 16;
  111             DO16(buf);
  112             buf += 16;
  113         }
  114         while (len--) {
  115             adler += *buf++;
  116             sum2 += adler;
  117         }
  118         MOD(adler);
  119         MOD(sum2);
  120     }
  121 
  122     /* return recombined sums */
  123     return adler | (sum2 << 16);
  124 }
  125 
  126 #ifdef ADLER32_COMBINE
  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 }
  150 #endif /* ADLER32_COMBINE */
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root/lib/libz/adler32.c

DEFINITIONS
