alpar@9: /* adler32.c -- compute the Adler-32 checksum of a data stream
alpar@9:  * Copyright (C) 1995-2007 Mark Adler
alpar@9:  * For conditions of distribution and use, see copyright notice in zlib.h
alpar@9:  */
alpar@9: 
alpar@9: /* @(#) $Id$ */
alpar@9: 
alpar@9: #include "zutil.h"
alpar@9: 
alpar@9: #define local static
alpar@9: 
alpar@9: local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2);
alpar@9: 
alpar@9: #define BASE 65521UL    /* largest prime smaller than 65536 */
alpar@9: #define NMAX 5552
alpar@9: /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
alpar@9: 
alpar@9: #define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}
alpar@9: #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
alpar@9: #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
alpar@9: #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
alpar@9: #define DO16(buf)   DO8(buf,0); DO8(buf,8);
alpar@9: 
alpar@9: /* use NO_DIVIDE if your processor does not do division in hardware */
alpar@9: #ifdef NO_DIVIDE
alpar@9: #  define MOD(a) \
alpar@9:     do { \
alpar@9:         if (a >= (BASE << 16)) a -= (BASE << 16); \
alpar@9:         if (a >= (BASE << 15)) a -= (BASE << 15); \
alpar@9:         if (a >= (BASE << 14)) a -= (BASE << 14); \
alpar@9:         if (a >= (BASE << 13)) a -= (BASE << 13); \
alpar@9:         if (a >= (BASE << 12)) a -= (BASE << 12); \
alpar@9:         if (a >= (BASE << 11)) a -= (BASE << 11); \
alpar@9:         if (a >= (BASE << 10)) a -= (BASE << 10); \
alpar@9:         if (a >= (BASE << 9)) a -= (BASE << 9); \
alpar@9:         if (a >= (BASE << 8)) a -= (BASE << 8); \
alpar@9:         if (a >= (BASE << 7)) a -= (BASE << 7); \
alpar@9:         if (a >= (BASE << 6)) a -= (BASE << 6); \
alpar@9:         if (a >= (BASE << 5)) a -= (BASE << 5); \
alpar@9:         if (a >= (BASE << 4)) a -= (BASE << 4); \
alpar@9:         if (a >= (BASE << 3)) a -= (BASE << 3); \
alpar@9:         if (a >= (BASE << 2)) a -= (BASE << 2); \
alpar@9:         if (a >= (BASE << 1)) a -= (BASE << 1); \
alpar@9:         if (a >= BASE) a -= BASE; \
alpar@9:     } while (0)
alpar@9: #  define MOD4(a) \
alpar@9:     do { \
alpar@9:         if (a >= (BASE << 4)) a -= (BASE << 4); \
alpar@9:         if (a >= (BASE << 3)) a -= (BASE << 3); \
alpar@9:         if (a >= (BASE << 2)) a -= (BASE << 2); \
alpar@9:         if (a >= (BASE << 1)) a -= (BASE << 1); \
alpar@9:         if (a >= BASE) a -= BASE; \
alpar@9:     } while (0)
alpar@9: #else
alpar@9: #  define MOD(a) a %= BASE
alpar@9: #  define MOD4(a) a %= BASE
alpar@9: #endif
alpar@9: 
alpar@9: /* ========================================================================= */
alpar@9: uLong ZEXPORT adler32(adler, buf, len)
alpar@9:     uLong adler;
alpar@9:     const Bytef *buf;
alpar@9:     uInt len;
alpar@9: {
alpar@9:     unsigned long sum2;
alpar@9:     unsigned n;
alpar@9: 
alpar@9:     /* split Adler-32 into component sums */
alpar@9:     sum2 = (adler >> 16) & 0xffff;
alpar@9:     adler &= 0xffff;
alpar@9: 
alpar@9:     /* in case user likes doing a byte at a time, keep it fast */
alpar@9:     if (len == 1) {
alpar@9:         adler += buf[0];
alpar@9:         if (adler >= BASE)
alpar@9:             adler -= BASE;
alpar@9:         sum2 += adler;
alpar@9:         if (sum2 >= BASE)
alpar@9:             sum2 -= BASE;
alpar@9:         return adler | (sum2 << 16);
alpar@9:     }
alpar@9: 
alpar@9:     /* initial Adler-32 value (deferred check for len == 1 speed) */
alpar@9:     if (buf == Z_NULL)
alpar@9:         return 1L;
alpar@9: 
alpar@9:     /* in case short lengths are provided, keep it somewhat fast */
alpar@9:     if (len < 16) {
alpar@9:         while (len--) {
alpar@9:             adler += *buf++;
alpar@9:             sum2 += adler;
alpar@9:         }
alpar@9:         if (adler >= BASE)
alpar@9:             adler -= BASE;
alpar@9:         MOD4(sum2);             /* only added so many BASE's */
alpar@9:         return adler | (sum2 << 16);
alpar@9:     }
alpar@9: 
alpar@9:     /* do length NMAX blocks -- requires just one modulo operation */
alpar@9:     while (len >= NMAX) {
alpar@9:         len -= NMAX;
alpar@9:         n = NMAX / 16;          /* NMAX is divisible by 16 */
alpar@9:         do {
alpar@9:             DO16(buf);          /* 16 sums unrolled */
alpar@9:             buf += 16;
alpar@9:         } while (--n);
alpar@9:         MOD(adler);
alpar@9:         MOD(sum2);
alpar@9:     }
alpar@9: 
alpar@9:     /* do remaining bytes (less than NMAX, still just one modulo) */
alpar@9:     if (len) {                  /* avoid modulos if none remaining */
alpar@9:         while (len >= 16) {
alpar@9:             len -= 16;
alpar@9:             DO16(buf);
alpar@9:             buf += 16;
alpar@9:         }
alpar@9:         while (len--) {
alpar@9:             adler += *buf++;
alpar@9:             sum2 += adler;
alpar@9:         }
alpar@9:         MOD(adler);
alpar@9:         MOD(sum2);
alpar@9:     }
alpar@9: 
alpar@9:     /* return recombined sums */
alpar@9:     return adler | (sum2 << 16);
alpar@9: }
alpar@9: 
alpar@9: /* ========================================================================= */
alpar@9: local uLong adler32_combine_(adler1, adler2, len2)
alpar@9:     uLong adler1;
alpar@9:     uLong adler2;
alpar@9:     z_off64_t len2;
alpar@9: {
alpar@9:     unsigned long sum1;
alpar@9:     unsigned long sum2;
alpar@9:     unsigned rem;
alpar@9: 
alpar@9:     /* the derivation of this formula is left as an exercise for the reader */
alpar@9:     rem = (unsigned)(len2 % BASE);
alpar@9:     sum1 = adler1 & 0xffff;
alpar@9:     sum2 = rem * sum1;
alpar@9:     MOD(sum2);
alpar@9:     sum1 += (adler2 & 0xffff) + BASE - 1;
alpar@9:     sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
alpar@9:     if (sum1 >= BASE) sum1 -= BASE;
alpar@9:     if (sum1 >= BASE) sum1 -= BASE;
alpar@9:     if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1);
alpar@9:     if (sum2 >= BASE) sum2 -= BASE;
alpar@9:     return sum1 | (sum2 << 16);
alpar@9: }
alpar@9: 
alpar@9: /* ========================================================================= */
alpar@9: uLong ZEXPORT adler32_combine(adler1, adler2, len2)
alpar@9:     uLong adler1;
alpar@9:     uLong adler2;
alpar@9:     z_off_t len2;
alpar@9: {
alpar@9:     return adler32_combine_(adler1, adler2, len2);
alpar@9: }
alpar@9: 
alpar@9: uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
alpar@9:     uLong adler1;
alpar@9:     uLong adler2;
alpar@9:     z_off64_t len2;
alpar@9: {
alpar@9:     return adler32_combine_(adler1, adler2, len2);
alpar@9: }