GY-63_MS5611/libraries/Fletcher/Fletcher.cpp
2023-10-30 17:03:06 +01:00

81 lines
1.8 KiB
C++

//
// FILE: Fletcher.cpp
// AUTHOR: Rob Tillaart
// VERSION: 0.1.9
// DATE: 2022-01-25
// PURPOSE: Arduino Library for calculating Fletcher's checksum
// URL: https://github.com/RobTillaart/Fletcher
// https://en.wikipedia.org/wiki/Fletcher%27s_checksum
#include "Fletcher.h"
// straightforward implementation.
// max length buffer 65534.
// Wikipedia shows optimizations.
//
uint16_t fletcher16(uint8_t *data, uint16_t length, uint32_t s1, uint32_t s2)
{
uint32_t _s1 = s1;
uint32_t _s2 = s2;
for (uint16_t i = 0; i < length;)
{
// if _s2 is halfway it is time to do modulo
while ((i < length) && (_s2 < 2147483648ULL)) // MAGIC NR
{
_s1 += data[i++];
_s2 += _s1;
}
// this optimization does not work due to the above "32-bit" loop.
// for all three functions.
// _s1 = (_s1 & 255) + (_s1 >> 8);
_s1 %= FLETCHER_16;
_s2 %= FLETCHER_16;
}
return (_s2 << 8) | _s1;
}
uint32_t fletcher32(uint16_t *data, uint16_t length, uint32_t s1, uint32_t s2)
{
uint32_t _s1 = s1;
uint32_t _s2 = s2;
for (uint16_t i = 0; i < length;)
{
// if _s2 is halfway it is time to do modulo
while ((i < length) && (_s2 < 2147483648ULL)) // MAGIC NR
{
_s1 += data[i++];
_s2 += _s1;
}
_s1 %= FLETCHER_32;
_s2 %= FLETCHER_32;
}
return (_s2 << 16) | _s1;
}
uint64_t fletcher64(uint32_t *data, uint16_t length, uint64_t s1, uint64_t s2)
{
uint64_t _s1 = s1;
uint64_t _s2 = s2;
for (uint16_t i = 0; i < length;)
{
// if _s2 is halfway it is time to do modulo
while ((i < length) && (_s2 < 9223372036854775808ULL)) // MAGIC NR
{
_s1 += data[i++];
_s2 += _s1;
}
_s1 %= FLETCHER_64;
_s2 %= FLETCHER_64;
}
return (_s2 << 32) | _s1;
}
// -- END OF FILE --