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// distribution boxbackup-0.11rc2 (svn version: 2072)
//
// Copyright (c) 2003 - 2008
// Ben Summers and contributors. All rights reserved.
//
// 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. All use of this software and associated advertising materials must
// display the following acknowledgment:
// This product includes software developed by Ben Summers.
// 4. The names of the Authors may not be used to endorse or promote
// products derived from this software without specific prior written
// permission.
//
// [Where legally impermissible the Authors do not disclaim liability for
// direct physical injury or death caused solely by defects in the software
// unless it is modified by a third party.]
//
// THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``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 AUTHORS 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.
//
//
//
// --------------------------------------------------------------------------
//
// 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;
}
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