calc.c

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/*
    clsync - file tree sync utility based on inotify/kqueue
 
    Copyright (C) 2014  Dmitry Yu Okunev <dyokunev@ut.mephi.ru> 0x8E30679C
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.
 
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
 
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#include "common.h"
 
#include "calc.h"
#include "error.h"
 
#ifdef HAVE_MHASH
#include <mhash.h>
#endif
 
#ifndef HAVE_MHASH
/**
 * @brief           Calculated Adler32 value for char array
 *
 * @param[in]   data        Pointer to data
 * @param[in]   len     Length of the data
 *
 * @retval  uint32_t    Adler32 value of data
 *
 */
 
// Copied from http://en.wikipedia.org/wiki/Adler-32
uint32_t adler32_calc ( const unsigned char *const data, uint32_t len ) // where data is the location of the data in physical
{
    // memory and len is the length of the data in bytes
    /*
        if (len&3)
            warning("len [%i] & 3 == %i != 0. Wrong length (not a multiple of 4).", len, len&3);
    */
    debug ( 70, "%p, %i", data, len );
    const int MOD_ADLER = 65521;
    uint32_t a = 1, b = 0;
    uint32_t index;
 
    // Process each byte of the data in order
    for ( index = 0; index < len; ++index ) {
        debug ( 80, "%5i: %02x %02x %02x", index, data[index], a, b );
        a = ( a + data[index] ) % MOD_ADLER;
        b = ( b + a ) % MOD_ADLER;
    }
 
    return ( b << 16 ) | a;
}
#endif