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134 lines
2.4 KiB
C++
134 lines
2.4 KiB
C++
//
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// FILE: Adler16.cpp
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// AUTHOR: Rob Tillaart
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// VERSION: 0.2.5
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// DATE: 2022-06-14
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// PURPOSE: Arduino Library for calculating Adler-16 checksum
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// URL: https://github.com/RobTillaart/Adler
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// https://en.wikipedia.org/wiki/Adler-32
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// (no Adler16 reference, implementation is experimental)
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#include "Adler16.h"
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Adler16::Adler16()
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{
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begin(1, 0);
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}
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void Adler16::begin(uint16_t s1, uint16_t s2)
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{
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_s1 = s1;
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_s2 = s2;
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_count = 0;
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}
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// reference implementation
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// void Adler16::add(uint8_t value)
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// {
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// _count++;
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// _s1 += value;
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// if (_s1 >= ADLER16_MOD_PRIME) _s1 -= ADLER16_MOD_PRIME;
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// _s2 += _s1;
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// if (_s2 >= ADLER16_MOD_PRIME) _s2 -= ADLER16_MOD_PRIME;
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// }
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// optimized version (~10% faster)
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void Adler16::add(uint8_t value)
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{
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_count++;
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_s1 += value;
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_s2 += _s1;
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if (_s2 >= ADLER16_MOD_PRIME)
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{
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_s2 -= ADLER16_MOD_PRIME;
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if (_s1 >= ADLER16_MOD_PRIME) _s1 -= ADLER16_MOD_PRIME;
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}
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}
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// straightforward going through the array.
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// small footprint
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// returns current Adler value
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uint16_t Adler16::add(uint8_t * array, uint16_t length)
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{
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while (length--)
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{
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add(*array++);
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}
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return (_s2 << 8) | _s1;
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}
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// Optimized version
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// S1 grows linear
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// S2 grows quadratic
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// only do modulo when S2 reaches halfway uint16_t
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// and at the end of the loop.
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// returns current Adler value
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uint16_t Adler16::addFast(uint8_t * array, uint16_t length)
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{
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_count += length;
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uint16_t s1 = _s1;
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uint16_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 < 32768)) // MAGIC NUMBER 2^15
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{
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s1 += array[i++];
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s2 += s1;
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}
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if (s2 >= ADLER16_MOD_PRIME)
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{
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s2 %= ADLER16_MOD_PRIME;
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if (s1 >= ADLER16_MOD_PRIME) s1 %= ADLER16_MOD_PRIME;
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}
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}
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_s1 = s1;
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_s2 = s2;
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return (s2 << 8) | s1;
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}
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uint16_t Adler16::getAdler()
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{
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return (_s2 << 8) | _s1;
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};
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uint16_t Adler16::count()
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{
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return _count;
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};
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//////////////////////////////////////////////////////////////
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//
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// wrappers for char arrays (strings).
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//
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void Adler16::add(char value)
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{
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add((uint8_t) value);
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}
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uint16_t Adler16::add(char * array, uint16_t length)
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{
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return add((uint8_t *) array, length);
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}
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uint16_t Adler16::addFast(char * array, uint16_t length)
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{
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return addFast((uint8_t *) array, length);
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}
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// -- END OF FILE --
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