vx32

Local 9vx git repository for patches.
git clone git://r-36.net/vx32
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adler32.c (4604B)

      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: adler32.c 1925 2005-10-06 19:32:02Z baford $ */
      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 }