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94 lines
2.3 KiB
C++
94 lines
2.3 KiB
C++
//
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// FILE: Fletcher.cpp
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// AUTHOR: Rob Tillaart
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// VERSION: 0.1.5
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// DATE: 2022-01-25
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// PURPOSE: Arduino Library for calculating Fletcher's checksum
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// URL: https://github.com/RobTillaart/Fletcher
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// https://en.wikipedia.org/wiki/Fletcher%27s_checksum
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//
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// HISTORY
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// 0.1.0 2022-01-25 initial version, straightforward implementation
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// 0.1.1 2022-01-26 optimize % math variation based upon to Anastase Nakassis (wikipedia)
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// 0.1.2 2022-01-26 add class implementation e.g. for streaming
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// 0.1.3 2022-04-15 fix #4 split .h in .h and .cpp
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// 0.1.4 2022-09-08 performance optimization (Kudos to Daniel Mohr).
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// affects SAMD, ESP32 and ESP8266
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// fix FLETCHER_LIB_VERSION
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// 0.1.5 2022-09-08 roll back the optimizations in the standalone functions
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// conflict with loop optimization already in.
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// update ketwords.txt
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#include "Fletcher.h"
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//
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// straightforward implementation.
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// max length buffer 65534.
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// Wikipedia shows optimizations.
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//
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uint16_t fletcher16(uint8_t *data, uint16_t length)
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{
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uint32_t s1 = 0;
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uint32_t s2 = 0;
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for (uint16_t i = 0; i < length;)
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{
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// if S2 is halfway it is time to do modulo
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while ((i < length) && (s2 < 2147483648ULL))
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{
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s1 += data[i++];
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s2 += s1;
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}
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s1 %= FLETCHER_16;
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// this optimization does not work due to the above "32-bit" loop.
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// for all three functions.
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// s1 = (s1 & 255) + (s1 >> 8);
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s2 %= FLETCHER_16;
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}
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return (s2 << 8) | s1;
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}
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uint32_t fletcher32(uint16_t *data, uint16_t length)
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{
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uint32_t s1 = 0;
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uint32_t s2 = 0;
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for (uint16_t i = 0; i < length;)
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{
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// if S2 is halfway it is time to do modulo
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while ((i < length) && (s2 < 2147483648ULL))
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{
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s1 += data[i++];
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s2 += s1;
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}
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s1 %= FLETCHER_32;
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s2 %= FLETCHER_32;
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}
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return (s2 << 16) | s1;
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}
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uint64_t fletcher64(uint32_t *data, uint16_t length)
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{
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uint64_t s1 = 0;
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uint64_t s2 = 0;
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for (uint16_t i = 0; i < length;)
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{
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// if S2 is halfway it is time to do modulo
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while ((i < length) && (s2 < 9223372036854775808ULL))
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{
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s1 += data[i++];
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s2 += s1;
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}
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s1 %= FLETCHER_64;
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s2 %= FLETCHER_64;
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}
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return (s2 << 32) | s1;
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}
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// -- END OF FILE --
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