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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. }
  170.