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81 lines
1.8 KiB
C++
81 lines
1.8 KiB
C++
//
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// FILE: Fletcher.cpp
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// AUTHOR: Rob Tillaart
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// VERSION: 0.1.8
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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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#include "Fletcher.h"
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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, uint32_t s1, uint32_t s2)
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{
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uint32_t _s1 = s1;
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uint32_t _s2 = s2;
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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)) // MAGIC NR
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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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// 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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_s1 %= FLETCHER_16;
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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, uint32_t s1, uint32_t s2)
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{
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uint32_t _s1 = s1;
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uint32_t _s2 = s2;
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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)) // MAGIC NR
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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, uint64_t s1, uint64_t s2)
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{
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uint64_t _s1 = s1;
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uint64_t _s2 = s2;
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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)) // MAGIC NR
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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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