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Annotation of embedaddon/rsync/zlib/adler32.c, revision 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: }