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Member "syslinux-6.03/com32/lib/zlib/adler32.c" (6 Oct 2014, 5048 Bytes) of package /linux/misc/syslinux-6.03.tar.gz:


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    1 /* adler32.c -- compute the Adler-32 checksum of a data stream
    2  * Copyright (C) 1995-2007 Mark Adler
    3  * For conditions of distribution and use, see copyright notice in zlib.h
    4  */
    5 
    6 /* @(#) $Id$ */
    7 
    8 #include "zutil.h"
    9 
   10 #define local static
   11 
   12 local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2);
   13 
   14 #define BASE 65521UL    /* largest prime smaller than 65536 */
   15 #define NMAX 5552
   16 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
   17 
   18 #define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}
   19 #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
   20 #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
   21 #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
   22 #define DO16(buf)   DO8(buf,0); DO8(buf,8);
   23 
   24 /* use NO_DIVIDE if your processor does not do division in hardware */
   25 #ifdef NO_DIVIDE
   26 #  define MOD(a) \
   27     do { \
   28         if (a >= (BASE << 16)) a -= (BASE << 16); \
   29         if (a >= (BASE << 15)) a -= (BASE << 15); \
   30         if (a >= (BASE << 14)) a -= (BASE << 14); \
   31         if (a >= (BASE << 13)) a -= (BASE << 13); \
   32         if (a >= (BASE << 12)) a -= (BASE << 12); \
   33         if (a >= (BASE << 11)) a -= (BASE << 11); \
   34         if (a >= (BASE << 10)) a -= (BASE << 10); \
   35         if (a >= (BASE << 9)) a -= (BASE << 9); \
   36         if (a >= (BASE << 8)) a -= (BASE << 8); \
   37         if (a >= (BASE << 7)) a -= (BASE << 7); \
   38         if (a >= (BASE << 6)) a -= (BASE << 6); \
   39         if (a >= (BASE << 5)) a -= (BASE << 5); \
   40         if (a >= (BASE << 4)) a -= (BASE << 4); \
   41         if (a >= (BASE << 3)) a -= (BASE << 3); \
   42         if (a >= (BASE << 2)) a -= (BASE << 2); \
   43         if (a >= (BASE << 1)) a -= (BASE << 1); \
   44         if (a >= BASE) a -= BASE; \
   45     } while (0)
   46 #  define MOD4(a) \
   47     do { \
   48         if (a >= (BASE << 4)) a -= (BASE << 4); \
   49         if (a >= (BASE << 3)) a -= (BASE << 3); \
   50         if (a >= (BASE << 2)) a -= (BASE << 2); \
   51         if (a >= (BASE << 1)) a -= (BASE << 1); \
   52         if (a >= BASE) a -= BASE; \
   53     } while (0)
   54 #else
   55 #  define MOD(a) a %= BASE
   56 #  define MOD4(a) a %= BASE
   57 #endif
   58 
   59 /* ========================================================================= */
   60 uLong ZEXPORT adler32(adler, buf, len)
   61     uLong adler;
   62     const Bytef *buf;
   63     uInt len;
   64 {
   65     unsigned long sum2;
   66     unsigned n;
   67 
   68     /* split Adler-32 into component sums */
   69     sum2 = (adler >> 16) & 0xffff;
   70     adler &= 0xffff;
   71 
   72     /* in case user likes doing a byte at a time, keep it fast */
   73     if (len == 1) {
   74         adler += buf[0];
   75         if (adler >= BASE)
   76             adler -= BASE;
   77         sum2 += adler;
   78         if (sum2 >= BASE)
   79             sum2 -= BASE;
   80         return adler | (sum2 << 16);
   81     }
   82 
   83     /* initial Adler-32 value (deferred check for len == 1 speed) */
   84     if (buf == Z_NULL)
   85         return 1L;
   86 
   87     /* in case short lengths are provided, keep it somewhat fast */
   88     if (len < 16) {
   89         while (len--) {
   90             adler += *buf++;
   91             sum2 += adler;
   92         }
   93         if (adler >= BASE)
   94             adler -= BASE;
   95         MOD4(sum2);             /* only added so many BASE's */
   96         return adler | (sum2 << 16);
   97     }
   98 
   99     /* do length NMAX blocks -- requires just one modulo operation */
  100     while (len >= NMAX) {
  101         len -= NMAX;
  102         n = NMAX / 16;          /* NMAX is divisible by 16 */
  103         do {
  104             DO16(buf);          /* 16 sums unrolled */
  105             buf += 16;
  106         } while (--n);
  107         MOD(adler);
  108         MOD(sum2);
  109     }
  110 
  111     /* do remaining bytes (less than NMAX, still just one modulo) */
  112     if (len) {                  /* avoid modulos if none remaining */
  113         while (len >= 16) {
  114             len -= 16;
  115             DO16(buf);
  116             buf += 16;
  117         }
  118         while (len--) {
  119             adler += *buf++;
  120             sum2 += adler;
  121         }
  122         MOD(adler);
  123         MOD(sum2);
  124     }
  125 
  126     /* return recombined sums */
  127     return adler | (sum2 << 16);
  128 }
  129 
  130 /* ========================================================================= */
  131 local uLong adler32_combine_(adler1, adler2, len2)
  132     uLong adler1;
  133     uLong adler2;
  134     z_off64_t len2;
  135 {
  136     unsigned long sum1;
  137     unsigned long sum2;
  138     unsigned rem;
  139 
  140     /* the derivation of this formula is left as an exercise for the reader */
  141     rem = (unsigned)(len2 % BASE);
  142     sum1 = adler1 & 0xffff;
  143     sum2 = rem * sum1;
  144     MOD(sum2);
  145     sum1 += (adler2 & 0xffff) + BASE - 1;
  146     sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
  147     if (sum1 >= BASE) sum1 -= BASE;
  148     if (sum1 >= BASE) sum1 -= BASE;
  149     if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1);
  150     if (sum2 >= BASE) sum2 -= BASE;
  151     return sum1 | (sum2 << 16);
  152 }
  153 
  154 /* ========================================================================= */
  155 uLong ZEXPORT adler32_combine(adler1, adler2, len2)
  156     uLong adler1;
  157     uLong adler2;
  158     z_off_t len2;
  159 {
  160     return adler32_combine_(adler1, adler2, len2);
  161 }
  162 
  163 uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
  164     uLong adler1;
  165     uLong adler2;
  166     z_off64_t len2;
  167 {
  168     return adler32_combine_(adler1, adler2, len2);
  169 }