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