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Initial revision

    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: adler32.c,v 1.1 2012/02/21 16:23:02 misho Exp $ */
    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: }