kernel/zmod/adler32.c

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