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Annotation of embedaddon/rsync/zlib/adler32.c, revision 1.1.1.1

1.1       misho       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: /* @(#) $Id$ */
                      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: }