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Diffstat (limited to 'lib/crypto/RollingChecksum.h')
| -rw-r--r-- | lib/crypto/RollingChecksum.h | 145 |
1 files changed, 145 insertions, 0 deletions
diff --git a/lib/crypto/RollingChecksum.h b/lib/crypto/RollingChecksum.h new file mode 100644 index 00000000..befc011f --- /dev/null +++ b/lib/crypto/RollingChecksum.h @@ -0,0 +1,145 @@ +// 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.h +// Purpose: A simple rolling checksum over a block of data +// Created: 6/12/03 +// +// -------------------------------------------------------------------------- + +#ifndef ROLLINGCHECKSUM__H +#define ROLLINGCHECKSUM__H + +// -------------------------------------------------------------------------- +// +// Class +// Name: RollingChecksum +// Purpose: A simple rolling checksum over a block of data -- can move the block +// "forwards" in memory and get the next checksum efficiently. +// +// Implementation of http://rsync.samba.org/tech_report/node3.html +// Created: 6/12/03 +// +// -------------------------------------------------------------------------- +class RollingChecksum +{ +public: + RollingChecksum(const void * const data, const unsigned int Length); + + // -------------------------------------------------------------------------- + // + // Function + // Name: RollingChecksum::RollForward(uint8_t, uint8_t, unsigned int) + // Purpose: Move the checksum forward a block, given the first byte of the current block, + // last byte of the next block (it's rolling forward to) and the length of the block. + // Created: 6/12/03 + // + // -------------------------------------------------------------------------- + inline void RollForward(const uint8_t StartOfThisBlock, const uint8_t LastOfNextBlock, const unsigned int Length) + { + // IMPLEMENTATION NOTE: Everything is implicitly mod 2^16 -- uint16_t's will overflow nicely. + a -= StartOfThisBlock; + a += LastOfNextBlock; + b -= Length * StartOfThisBlock; + b += a; + } + + // -------------------------------------------------------------------------- + // + // 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 RollForwardSeveral(const uint8_t * const StartOfThisBlock, const uint8_t * const LastOfNextBlock, const unsigned int Length, const unsigned int Skip); + + // -------------------------------------------------------------------------- + // + // Function + // Name: RollingChecksum::GetChecksum() + // Purpose: Returns the checksum + // Created: 6/12/03 + // + // -------------------------------------------------------------------------- + inline uint32_t GetChecksum() const + { + return ((uint32_t)a) | (((uint32_t)b) << 16); + } + + // Components, just in case they're handy + inline uint16_t GetComponent1() const {return a;} + inline uint16_t GetComponent2() const {return b;} + + // -------------------------------------------------------------------------- + // + // Function + // Name: RollingChecksum::GetComponentForHashing() + // Purpose: Return the 16 bit component used for hashing and/or quick checks + // Created: 6/12/03 + // + // -------------------------------------------------------------------------- + inline uint16_t GetComponentForHashing() const + { + return b; + } + + // -------------------------------------------------------------------------- + // + // Function + // Name: RollingChecksum::ExtractHashingComponent(uint32_t) + // Purpose: Static. Given a full checksum, extract the component used in the hashing table. + // Created: 14/1/04 + // + // -------------------------------------------------------------------------- + static inline uint16_t ExtractHashingComponent(const uint32_t Checksum) + { + return Checksum >> 16; + } + +private: + uint16_t a; + uint16_t b; +}; + +#endif // ROLLINGCHECKSUM__H + |