diff options
author | Reinhard Tartler <siretart@tauware.de> | 2007-02-14 09:01:45 +0100 |
---|---|---|
committer | Reinhard Tartler <siretart@tauware.de> | 2007-02-14 09:01:45 +0100 |
commit | aa2943800f9c00823720af98da036813ebf5cd2c (patch) | |
tree | 099cc0264d32a36ab89aa3f48cbf34612c3cd225 /lib/crypto/RollingChecksum.cpp |
initial commit
Diffstat (limited to 'lib/crypto/RollingChecksum.cpp')
-rw-r--r-- | lib/crypto/RollingChecksum.cpp | 100 |
1 files changed, 100 insertions, 0 deletions
diff --git a/lib/crypto/RollingChecksum.cpp b/lib/crypto/RollingChecksum.cpp new file mode 100644 index 00000000..73e85319 --- /dev/null +++ b/lib/crypto/RollingChecksum.cpp @@ -0,0 +1,100 @@ +// distribution boxbackup-0.10 (svn version: 494) +// +// Copyright (c) 2003 - 2006 +// 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; +} |