6.7 KiB
Adler
Arduino Library for Adler-32 and experimental Adler-16 checksum.
Description
This library provides a Adler32 checksum of a data array. Furthermore since 0.2.0 an experimental Adler-16 implementation is added. This one is often faster as it uses a smaller checksum than the Adler32, and the price is that it is less sensitive than the Adler32. Still it might have its niches where it will be useful.
Relates to https://github.com/RobTillaart/CRC
Relates to https://github.com/RobTillaart/Fletcher
Tested on Arduino UNO only.
0.2.0 is a breaking change, file names have been changed to be more in line with the CRC library.
- Adler.h for the static functions
- Adler32.h for the Adler32 class
- Adler16.h for the Adler16 class.
Interface
Adler class
Use #include "Adler32.h" or #include "Adler16.h"
The interface for the Adler16 is very similar.
- Adler32() Constructor, initializes internals.
- void begin(uint8_t s1 = 1, uint8_t s2 = 0) resets the internals. optional setting start values for s1 and s2. Note this is not part of the standard. This allows a restart from a specific index in a buffer.
- 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.
- void addFast(const uint8_t * array, uint8_t length) add an array of values to the checksum. Is faster by trading PROGMEM for performance.
- uint32_t getAdler() get the current checksum.
- uint32_t count() get the number of items added. Merely a debugging feature, can overflow without affecting checksum.
The class is typically used for streaming very large blocks of data, optional with intermediate checksum tests.
Performance Adler32
Not tested ESP32 (and many other platforms) yet.
Numbers measured with Adler32_performance.ino.
add(value)
The add(value) adds one byte and does a subtraction instead of a modulo.
| Version | Function | UNO 16 MHz | ESP32 240 MHz |
|---|---|---|---|
| 0.1.0 | add | 5.6 us | |
| 0.1.2 | add | 6.6 us | |
| 0.2.0 | add | 5.9 us |
add(lorem) 868 chars
The add(array, length) is a straightforward loop over the array and has a small footprint.
| Version | Function | UNO 16 MHz | ESP32 240 MHz |
|---|---|---|---|
| 0.1.0 | add | ||
| 0.1.2 | add | 6392 us | |
| 0.2.0 | add | 5748 us |
Note: add() is about 6.6 us per byte.
addFast(lorem) 868 chars
The addFast(array, length) is faster than the reference add(array, length) and uses 108 bytes more. So the function has a larger footprint. Depending on your needs, choose performance or footprint.
See Adler32_performance_addFast.ino
| Version | Function | UNO 16 MHz | ESP32 240 MHz |
|---|---|---|---|
| 0.1.0 | addFast | ||
| 0.1.2 | addFast | 1348 us | |
| 0.2.0 | addFast | 1348 us |
Note: addFast() is less than 2 us per byte.
Performance Adler16
Not tested ESP32 (and many other platforms) yet.
Numbers measured with Adler16_performance.ino.
add(value)
The add(value) adds one byte and does a subtraction instead of a modulo.
| Version | Function | UNO 16 MHz | ESP32 240 MHz |
|---|---|---|---|
| 0.2.0 | add | 4.0 us |
The per byte performance of the Adler16 (on UNO) is faster than the Adler32 add(value). The reason is that a 16 bit subtraction on an UNO is faster than a 32 bit subtraction.
add(lorem) 868 chars
The add(array, length) is a straightforward loop over the array and has a small footprint.
| Version | Function | UNO 16 MHz | ESP32 240 MHz |
|---|---|---|---|
| 0.2.0 | add | 4040 us |
Note: add() is about 6.6 us per byte.
addFast(lorem) 868 chars
The addFast(array, length) is faster than the reference add(array, length).
| Version | Function | UNO 16 MHz | ESP32 240 MHz |
|---|---|---|---|
| 0.2.0 | addFast | 1968 us |
The gain of the faster 16 bit modulo meets the frequency of doing the modulo more often.
Interface static functions
The functions are straightforward.
Use #include "Adler.h"
- uint32_t adler32(uint8_t *data, uint16_t length) length in units of 1 byte = 8 bits.
- uint16_t adler16(uint8_t *data, uint16_t length) length in units of 1 byte = 8 bits.
The functions are typically used for an in memory buffer to calculate the checksum once. Think of packets in a network, records in a database, or a checksum for an configuration in EEPROM.
Performance
Not tested ESP32 (and many other platforms) yet.
Numbers measured with Adler_performance.ino.
Lorem Ipsum text = 868 bytes.
| Version | Function | UNO 16 MHz | ESP32 240 MHz |
|---|---|---|---|
| 0.1.0 | Adler32 | 1116 us | |
| 0.1.2 | Adler32 | 1116 us | |
| 0.2.0 | Adler32 | 1116 us | |
| 0.2.0 | Adler16 | 1736 us |
Adler32 average 1116 / 868 = 1.29 us per byte. Adler16 average 1736 / 868 = 2.00 us per byte. (~1.5x slower !)
Adler16 does more often the modulo math as it reaches halfway uint16_t faster than Adler32 reaches halfway uint32_t.
As the Adler16 is less performant as the Adler32, it is often the best to use the 32 bit version.
Operation
See examples.
Future
- return values for add(array) and addFast(array)
- updated checksum?
- not for add(value) as that would create quite some overhead.
- Adler64 ?
- would need a large prime (which)
Wont
- do the string wrappers need strlen() ? parameter.
- yes, as string can be processed partially.