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  1. /* adler32.c -- compute the Adler-32 checksum of a data stream
  2.  * Copyright (C) 1995-2011 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_ OF((uLong adler1, uLong adler2, z_off64_t len2));
  13.  
  14. #define BASE 65521      /* 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.    try it both ways to see which is faster */
  26. #ifdef NO_DIVIDE
  27. /* note that this assumes BASE is 65521, where 65536 % 65521 == 15
  28.    (thank you to John Reiser for pointing this out) */
  29. #  define CHOP(a) \
  30.     do { \
  31.         unsigned long tmp = a >> 16; \
  32.         a &= 0xffffUL; \
  33.         a += (tmp << 4) - tmp; \
  34.     } while (0)
  35. #  define MOD28(a) \
  36.     do { \
  37.         CHOP(a); \
  38.         if (a >= BASE) a -= BASE; \
  39.     } while (0)
  40. #  define MOD(a) \
  41.     do { \
  42.         CHOP(a); \
  43.         MOD28(a); \
  44.     } while (0)
  45. #  define MOD63(a) \
  46.     do { /* this assumes a is not negative */ \
  47.         z_off64_t tmp = a >> 32; \
  48.         a &= 0xffffffffL; \
  49.         a += (tmp << 8) - (tmp << 5) + tmp; \
  50.         tmp = a >> 16; \
  51.         a &= 0xffffL; \
  52.         a += (tmp << 4) - tmp; \
  53.         tmp = a >> 16; \
  54.         a &= 0xffffL; \
  55.         a += (tmp << 4) - tmp; \
  56.         if (a >= BASE) a -= BASE; \
  57.     } while (0)
  58. #else
  59. #  define MOD(a) a %= BASE
  60. #  define MOD28(a) a %= BASE
  61. #  define MOD63(a) a %= BASE
  62. #endif
  63.  
  64. /* ========================================================================= */
  65. uLong ZEXPORT adler32(adler, buf, len)
  66.     uLong adler;
  67.     const Bytef *buf;
  68.     uInt len;
  69. {
  70.     unsigned long sum2;
  71.     unsigned n;
  72.  
  73.     /* split Adler-32 into component sums */
  74.     sum2 = (adler >> 16) & 0xffff;
  75.     adler &= 0xffff;
  76.  
  77.     /* in case user likes doing a byte at a time, keep it fast */
  78.     if (len == 1) {
  79.         adler += buf[0];
  80.         if (adler >= BASE)
  81.             adler -= BASE;
  82.         sum2 += adler;
  83.         if (sum2 >= BASE)
  84.             sum2 -= BASE;
  85.         return adler | (sum2 << 16);
  86.     }
  87.  
  88.     /* initial Adler-32 value (deferred check for len == 1 speed) */
  89.     if (buf == Z_NULL)
  90.         return 1L;
  91.  
  92.     /* in case short lengths are provided, keep it somewhat fast */
  93.     if (len < 16) {
  94.         while (len--) {
  95.             adler += *buf++;
  96.             sum2 += adler;
  97.         }
  98.         if (adler >= BASE)
  99.             adler -= BASE;
  100.         MOD28(sum2);            /* only added so many BASE's */
  101.         return adler | (sum2 << 16);
  102.     }
  103.  
  104.     /* do length NMAX blocks -- requires just one modulo operation */
  105.     while (len >= NMAX) {
  106.         len -= NMAX;
  107.         n = NMAX / 16;          /* NMAX is divisible by 16 */
  108.         do {
  109.             DO16(buf);          /* 16 sums unrolled */
  110.             buf += 16;
  111.         } while (--n);
  112.         MOD(adler);
  113.         MOD(sum2);
  114.     }
  115.  
  116.     /* do remaining bytes (less than NMAX, still just one modulo) */
  117.     if (len) {                  /* avoid modulos if none remaining */
  118.         while (len >= 16) {
  119.             len -= 16;
  120.             DO16(buf);
  121.             buf += 16;
  122.         }
  123.         while (len--) {
  124.             adler += *buf++;
  125.             sum2 += adler;
  126.         }
  127.         MOD(adler);
  128.         MOD(sum2);
  129.     }
  130.  
  131.     /* return recombined sums */
  132.     return adler | (sum2 << 16);
  133. }
  134.  
  135. /* ========================================================================= */
  136. local uLong adler32_combine_(adler1, adler2, len2)
  137.     uLong adler1;
  138.     uLong adler2;
  139.     z_off64_t len2;
  140. {
  141.     unsigned long sum1;
  142.     unsigned long sum2;
  143.     unsigned rem;
  144.  
  145.     /* for negative len, return invalid adler32 as a clue for debugging */
  146.     if (len2 < 0)
  147.         return 0xffffffffUL;
  148.  
  149.     /* the derivation of this formula is left as an exercise for the reader */
  150.     MOD63(len2);                /* assumes len2 >= 0 */
  151.     rem = (unsigned)len2;
  152.     sum1 = adler1 & 0xffff;
  153.     sum2 = rem * sum1;
  154.     MOD(sum2);
  155.     sum1 += (adler2 & 0xffff) + BASE - 1;
  156.     sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
  157.     if (sum1 >= BASE) sum1 -= BASE;
  158.     if (sum1 >= BASE) sum1 -= BASE;
  159.     if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1);
  160.     if (sum2 >= BASE) sum2 -= BASE;
  161.     return sum1 | (sum2 << 16);
  162. }
  163.  
  164. /* ========================================================================= */
  165. uLong ZEXPORT adler32_combine(adler1, adler2, len2)
  166.     uLong adler1;
  167.     uLong adler2;
  168.     z_off_t len2;
  169. {
  170.     return adler32_combine_(adler1, adler2, len2);
  171. }
  172.  
  173. uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
  174.     uLong adler1;
  175.     uLong adler2;
  176.     z_off64_t len2;
  177. {
  178.     return adler32_combine_(adler1, adler2, len2);
  179. }
  180.