/* adler32.c -- compute the Adler-32 checksum of a data stream * Copyright (C) 1995-2004 Mark Adler * For conditions of distribution and use, see copyright notice in zlib.h *//* @(#) $Id: adler32.c,v 1.1 2005/09/23 22:39:00 beng Exp $ */#define ZLIB_INTERNAL#include "zlib.h"#define BASE 65521UL    /* largest prime smaller than 65536 */#define NMAX 5552/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */#define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}#define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);#define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);#define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);#define DO16(buf)   DO8(buf,0); DO8(buf,8);/* use NO_DIVIDE if your processor does not do division in hardware */#ifdef NO_DIVIDE#  define MOD(a) \    do { \        if (a >= (BASE << 16)) a -= (BASE << 16); \        if (a >= (BASE << 15)) a -= (BASE << 15); \        if (a >= (BASE << 14)) a -= (BASE << 14); \        if (a >= (BASE << 13)) a -= (BASE << 13); \        if (a >= (BASE << 12)) a -= (BASE << 12); \        if (a >= (BASE << 11)) a -= (BASE << 11); \        if (a >= (BASE << 10)) a -= (BASE << 10); \        if (a >= (BASE << 9)) a -= (BASE << 9); \        if (a >= (BASE << 8)) a -= (BASE << 8); \        if (a >= (BASE << 7)) a -= (BASE << 7); \        if (a >= (BASE << 6)) a -= (BASE << 6); \        if (a >= (BASE << 5)) a -= (BASE << 5); \        if (a >= (BASE << 4)) a -= (BASE << 4); \        if (a >= (BASE << 3)) a -= (BASE << 3); \        if (a >= (BASE << 2)) a -= (BASE << 2); \        if (a >= (BASE << 1)) a -= (BASE << 1); \        if (a >= BASE) a -= BASE; \    } while (0)#  define MOD4(a) \    do { \        if (a >= (BASE << 4)) a -= (BASE << 4); \        if (a >= (BASE << 3)) a -= (BASE << 3); \        if (a >= (BASE << 2)) a -= (BASE << 2); \        if (a >= (BASE << 1)) a -= (BASE << 1); \        if (a >= BASE) a -= BASE; \    } while (0)#else#  define MOD(a) a %= BASE#  define MOD4(a) a %= BASE#endif/* ========================================================================= */uLong ZEXPORT adler32(adler, buf, len)    uLong adler;    const Bytef *buf;    uInt len;{    unsigned long sum2;    unsigned n;    /* split Adler-32 into component sums */    sum2 = (adler >> 16) & 0xffff;    adler &= 0xffff;    /* in case user likes doing a byte at a time, keep it fast */    if (len == 1) {        adler += buf[0];        if (adler >= BASE)            adler -= BASE;        sum2 += adler;        if (sum2 >= BASE)            sum2 -= BASE;        return adler | (sum2 << 16);    }    /* initial Adler-32 value (deferred check for len == 1 speed) */    if (buf == Z_NULL)        return 1L;    /* in case short lengths are provided, keep it somewhat fast */    if (len < 16) {        while (len--) {            adler += *buf++;            sum2 += adler;        }        if (adler >= BASE)            adler -= BASE;        MOD4(sum2);             /* only added so many BASE's */        return adler | (sum2 << 16);    }    /* do length NMAX blocks -- requires just one modulo operation */    while (len >= NMAX) {        len -= NMAX;        n = NMAX / 16;          /* NMAX is divisible by 16 */        do {            DO16(buf);          /* 16 sums unrolled */            buf += 16;        } while (--n);        MOD(adler);        MOD(sum2);    }    /* do remaining bytes (less than NMAX, still just one modulo) */    if (len) {                  /* avoid modulos if none remaining */        while (len >= 16) {            len -= 16;            DO16(buf);            buf += 16;        }        while (len--) {            adler += *buf++;            sum2 += adler;        }        MOD(adler);        MOD(sum2);    }    /* return recombined sums */    return adler | (sum2 << 16);}/* ========================================================================= */uLong ZEXPORT adler32_combine(adler1, adler2, len2)    uLong adler1;    uLong adler2;    z_off_t len2;{    unsigned long sum1;    unsigned long sum2;    unsigned rem;    /* the derivation of this formula is left as an exercise for the reader */    rem = (unsigned)(len2 % BASE);    sum1 = adler1 & 0xffff;    sum2 = rem * sum1;    MOD(sum2);    sum1 += (adler2 & 0xffff) + BASE - 1;    sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;    if (sum1 > BASE) sum1 -= BASE;    if (sum1 > BASE) sum1 -= BASE;    if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);    if (sum2 > BASE) sum2 -= BASE;    return sum1 | (sum2 << 16);}