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118 lines
4.1 KiB
Markdown
118 lines
4.1 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/FLETCHER/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/FLETCHER/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/FLETCHER/blob/master/LICENSE)
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[](https://github.com/RobTillaart/FLETCHER/releases)
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# FLETCHER
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Arduino Library for Fletcher's checksum
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## Description
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This library provides a Fletcher checksum of a data array.
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Fletcher's checksum is in general faster than CRC but possibly not as
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good in detecting errors.
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See https://en.wikipedia.org/wiki/Fletcher%27s_checksum for details.
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Relates to https://github.com/RobTillaart/CRC
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Use https://github.com/RobTillaart/printHelpers to print the Fletcher64().
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Tested on Arduino UNO + ESP32 + SAMD (See PR #7).
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## Interface
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## Fletcher16
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These interfaces are very similar for Fletcher16, Fletcher32 and Fletcher64 class.
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Use **\#include "Fletcher16.h"**
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- **Fletcher16()** Constructor, initializes internals.
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- **void begin(uint8_t s1 = 0, uint8_t s2 = 0)** resets the internals.
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optional setting start values for s1 and s2. Note this is not part of the standard.
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- **void add(uint8_t value)** add a single value to the checksum.
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- **void add(const uint8_t \* array, uint8_t length)** add an array of values to the checksum.
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- **uint16_t getFletcher()** get the current checksum.
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- **uint32_t count()** get the number of items added. Merely a debugging feature, can overflow without affecting checksum.
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The checksum from **getFletcher()** can be split into a high and a low part
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to be used to "feed" **begin()** again. See restart example.
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## Interface static functions
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The functions are straightforward, however one should define **length**
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in terms of the data type and optional pad it with zeros.
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A string "abcdef" has length 2 for **fletcher64()** as it needs 2x4 bytes.
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Use **\#include "Fletcher.h"**
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- **uint16_t fletcher16(uint8_t \*data, uint16_t length)** length in units of 1 byte = 8 bits.
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- **uint32_t fletcher32(uint16_t \*data, uint16_t length)** length in units of 2 bytes = 16 bits.
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- **uint64_t fletcher64(uint32_t \*data, uint16_t length)** length in units of 4 bytes = 32 bits.
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#### Performance I
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Not tested ESP32 (and many other platforms) yet.
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First numbers of **.add(value)** measured with test sketch shows the following timing.
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| Checksum | UNO 16 MHz | ESP32 240 MHz |
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|:------------|:-----------:|:-------------:|
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| Fletcher16 | 3.8 us | 0.22 us |
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| Fletcher32 | 5.6 us | 0.23 us |
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| Fletcher64 | 10.1 us | 0.26 us |
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| Average | 6.5 us | 0.24 us |
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#### Performance II
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Not tested extensively, first numbers of **.add(array, length)**
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measured with **Fletcher_performance.ino** sketch shows the following timing.
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Lorem Ipsum text = 868 bytes.
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Version 0.1.3.
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| Checksum | UNO 16 MHz | ESP32 240 MHz | Notes |
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|:------------|:-----------:|:-------------:|:-------------------|
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| Fletcher16 | 1120 us | 62 us | first run slower ? |
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| Fletcher32 | 728 us | 33 us | |
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| Fletcher64 | 1952 us | 35 us | |
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| Average | 1267 us | 43 us | |
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| Avg / char | 1.46 us | 0.0495 us | 868 bytes |
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Note 0.1.4 has improved the performance. See PR #7 for some numbers.
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## Operation
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See examples.
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## Future ideas
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- improve documentation
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- update performance figures.
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- test other platforms
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- others e.g. Fletcher24?
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- generic FletcherN(). for N = 1..32
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- add Print interface
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- or Printable() ?
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- Stream ??
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- add getters for S1 and S2 in the classes
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- add parameter for start values for F in static functions
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- would allow to use them in a stream too.
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