// distribution boxbackup-0.11.1 (svn version: 2821_2827)
// Box Backup, http://www.boxbackup.org/
// 
// Copyright (c) 2003-2010, Ben Summers and contributors.
// All rights reserved.
// 
// Note that this project uses mixed licensing. Any file with this license
// attached, or where the code LICENSE-DUAL appears on the first line, falls
// under this license. See the file COPYING.txt for more information.
// 
// This file is dual licensed. You may use and distribute it providing that you
// comply EITHER with the terms of the BSD license, OR the GPL license. It is
// not necessary to comply with both licenses, only one.
// 
// The BSD license option follows:
// 
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
// 
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
//  
// 3. Neither the name of the Box Backup nor the names of its contributors may
//    be used to endorse or promote products derived from this software without
//    specific prior written permission.
// 
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE FOR ANY
// DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
// ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
// THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// 
// [http://en.wikipedia.org/wiki/BSD_licenses#3-clause_license_.28.22New_BSD_License.22.29]
// 
// The GPL license option follows:
// 
// 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 2
// 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, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
// 
// [http://www.gnu.org/licenses/old-licenses/gpl-2.0.html#SEC4]
// --------------------------------------------------------------------------
//
// File
//		Name:    RollingChecksum.cpp
//		Purpose: A simple rolling checksum over a block of data
//		Created: 6/12/03
//
// --------------------------------------------------------------------------

#include "Box.h"
#include "RollingChecksum.h"

#include "MemLeakFindOn.h"

// --------------------------------------------------------------------------
//
// Function
//		Name:    RollingChecksum::RollingChecksum(const void *, unsigned int)
//		Purpose: Constructor -- does initial computation of the checksum.
//		Created: 6/12/03
//
// --------------------------------------------------------------------------
RollingChecksum::RollingChecksum(const void * const data, const unsigned int Length)
	: a(0),
	  b(0)
{
	const uint8_t *block = (const uint8_t *)data;
	for(unsigned int x = Length; x >= 1; --x)
	{
		a += (*block);
		b += x * (*block);
		
		++block;
	}
}

// --------------------------------------------------------------------------
//
// Function
//		Name:    RollingChecksum::RollForwardSeveral(uint8_t*, uint8_t*, unsigned int, unsigned int)
//		Purpose: Move the checksum forward a block, given a pointer to the first byte of the current block,
//				 and a pointer just after the last byte of the current block and the length of the block and of the skip.
//		Created: 7/14/05
//
// --------------------------------------------------------------------------
void RollingChecksum::RollForwardSeveral(const uint8_t * const StartOfThisBlock, const uint8_t * const LastOfNextBlock, const unsigned int Length, const unsigned int Skip)
{
	// IMPLEMENTATION NOTE: Everything is implicitly mod 2^16 -- uint16_t's will overflow nicely.
	unsigned int i;
	uint16_t sumBegin=0, j,k;

	for(i=0; i < Skip; i++)
	{
		j = StartOfThisBlock[i];
		k = LastOfNextBlock[i];
		sumBegin += j;
		a += (k - j);
		b += a;
	}

	b -= Length * sumBegin;
}
