nuclear@1: /* adler32.c -- compute the Adler-32 checksum of a data stream
nuclear@1:  * Copyright (C) 1995-2004 Mark Adler
nuclear@1:  * For conditions of distribution and use, see copyright notice in zlib.h
nuclear@1:  */
nuclear@1: 
nuclear@1: /* @(#) $Id$ */
nuclear@1: 
nuclear@1: #define ZLIB_INTERNAL
nuclear@1: #include "zlib.h"
nuclear@1: 
nuclear@1: #define BASE 65521UL    /* largest prime smaller than 65536 */
nuclear@1: #define NMAX 5552
nuclear@1: /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
nuclear@1: 
nuclear@1: #define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}
nuclear@1: #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
nuclear@1: #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
nuclear@1: #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
nuclear@1: #define DO16(buf)   DO8(buf,0); DO8(buf,8);
nuclear@1: 
nuclear@1: /* use NO_DIVIDE if your processor does not do division in hardware */
nuclear@1: #ifdef NO_DIVIDE
nuclear@1: #  define MOD(a) \
nuclear@1:     do { \
nuclear@1:         if (a >= (BASE << 16)) a -= (BASE << 16); \
nuclear@1:         if (a >= (BASE << 15)) a -= (BASE << 15); \
nuclear@1:         if (a >= (BASE << 14)) a -= (BASE << 14); \
nuclear@1:         if (a >= (BASE << 13)) a -= (BASE << 13); \
nuclear@1:         if (a >= (BASE << 12)) a -= (BASE << 12); \
nuclear@1:         if (a >= (BASE << 11)) a -= (BASE << 11); \
nuclear@1:         if (a >= (BASE << 10)) a -= (BASE << 10); \
nuclear@1:         if (a >= (BASE << 9)) a -= (BASE << 9); \
nuclear@1:         if (a >= (BASE << 8)) a -= (BASE << 8); \
nuclear@1:         if (a >= (BASE << 7)) a -= (BASE << 7); \
nuclear@1:         if (a >= (BASE << 6)) a -= (BASE << 6); \
nuclear@1:         if (a >= (BASE << 5)) a -= (BASE << 5); \
nuclear@1:         if (a >= (BASE << 4)) a -= (BASE << 4); \
nuclear@1:         if (a >= (BASE << 3)) a -= (BASE << 3); \
nuclear@1:         if (a >= (BASE << 2)) a -= (BASE << 2); \
nuclear@1:         if (a >= (BASE << 1)) a -= (BASE << 1); \
nuclear@1:         if (a >= BASE) a -= BASE; \
nuclear@1:     } while (0)
nuclear@1: #  define MOD4(a) \
nuclear@1:     do { \
nuclear@1:         if (a >= (BASE << 4)) a -= (BASE << 4); \
nuclear@1:         if (a >= (BASE << 3)) a -= (BASE << 3); \
nuclear@1:         if (a >= (BASE << 2)) a -= (BASE << 2); \
nuclear@1:         if (a >= (BASE << 1)) a -= (BASE << 1); \
nuclear@1:         if (a >= BASE) a -= BASE; \
nuclear@1:     } while (0)
nuclear@1: #else
nuclear@1: #  define MOD(a) a %= BASE
nuclear@1: #  define MOD4(a) a %= BASE
nuclear@1: #endif
nuclear@1: 
nuclear@1: /* ========================================================================= */
nuclear@1: uLong ZEXPORT adler32(adler, buf, len)
nuclear@1:     uLong adler;
nuclear@1:     const Bytef *buf;
nuclear@1:     uInt len;
nuclear@1: {
nuclear@1:     unsigned long sum2;
nuclear@1:     unsigned n;
nuclear@1: 
nuclear@1:     /* split Adler-32 into component sums */
nuclear@1:     sum2 = (adler >> 16) & 0xffff;
nuclear@1:     adler &= 0xffff;
nuclear@1: 
nuclear@1:     /* in case user likes doing a byte at a time, keep it fast */
nuclear@1:     if (len == 1) {
nuclear@1:         adler += buf[0];
nuclear@1:         if (adler >= BASE)
nuclear@1:             adler -= BASE;
nuclear@1:         sum2 += adler;
nuclear@1:         if (sum2 >= BASE)
nuclear@1:             sum2 -= BASE;
nuclear@1:         return adler | (sum2 << 16);
nuclear@1:     }
nuclear@1: 
nuclear@1:     /* initial Adler-32 value (deferred check for len == 1 speed) */
nuclear@1:     if (buf == Z_NULL)
nuclear@1:         return 1L;
nuclear@1: 
nuclear@1:     /* in case short lengths are provided, keep it somewhat fast */
nuclear@1:     if (len < 16) {
nuclear@1:         while (len--) {
nuclear@1:             adler += *buf++;
nuclear@1:             sum2 += adler;
nuclear@1:         }
nuclear@1:         if (adler >= BASE)
nuclear@1:             adler -= BASE;
nuclear@1:         MOD4(sum2);             /* only added so many BASE's */
nuclear@1:         return adler | (sum2 << 16);
nuclear@1:     }
nuclear@1: 
nuclear@1:     /* do length NMAX blocks -- requires just one modulo operation */
nuclear@1:     while (len >= NMAX) {
nuclear@1:         len -= NMAX;
nuclear@1:         n = NMAX / 16;          /* NMAX is divisible by 16 */
nuclear@1:         do {
nuclear@1:             DO16(buf);          /* 16 sums unrolled */
nuclear@1:             buf += 16;
nuclear@1:         } while (--n);
nuclear@1:         MOD(adler);
nuclear@1:         MOD(sum2);
nuclear@1:     }
nuclear@1: 
nuclear@1:     /* do remaining bytes (less than NMAX, still just one modulo) */
nuclear@1:     if (len) {                  /* avoid modulos if none remaining */
nuclear@1:         while (len >= 16) {
nuclear@1:             len -= 16;
nuclear@1:             DO16(buf);
nuclear@1:             buf += 16;
nuclear@1:         }
nuclear@1:         while (len--) {
nuclear@1:             adler += *buf++;
nuclear@1:             sum2 += adler;
nuclear@1:         }
nuclear@1:         MOD(adler);
nuclear@1:         MOD(sum2);
nuclear@1:     }
nuclear@1: 
nuclear@1:     /* return recombined sums */
nuclear@1:     return adler | (sum2 << 16);
nuclear@1: }
nuclear@1: 
nuclear@1: /* ========================================================================= */
nuclear@1: uLong ZEXPORT adler32_combine(adler1, adler2, len2)
nuclear@1:     uLong adler1;
nuclear@1:     uLong adler2;
nuclear@1:     z_off_t len2;
nuclear@1: {
nuclear@1:     unsigned long sum1;
nuclear@1:     unsigned long sum2;
nuclear@1:     unsigned rem;
nuclear@1: 
nuclear@1:     /* the derivation of this formula is left as an exercise for the reader */
nuclear@1:     rem = (unsigned)(len2 % BASE);
nuclear@1:     sum1 = adler1 & 0xffff;
nuclear@1:     sum2 = rem * sum1;
nuclear@1:     MOD(sum2);
nuclear@1:     sum1 += (adler2 & 0xffff) + BASE - 1;
nuclear@1:     sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
nuclear@1:     if (sum1 > BASE) sum1 -= BASE;
nuclear@1:     if (sum1 > BASE) sum1 -= BASE;
nuclear@1:     if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
nuclear@1:     if (sum2 > BASE) sum2 -= BASE;
nuclear@1:     return sum1 | (sum2 << 16);
nuclear@1: }