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GY-63_MS5611/libraries/Adler/README.md
rob tillaart a8bd32dc42 0.1.2 Adler
2022-06-14 15:28:07 +02:00

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Arduino CI Arduino-lint JSON check License: MIT GitHub release

Adler

Arduino Library for Adler-32 checksum

Description

This library provides a Adler checksum of a data array.

Relates to https://github.com/RobTillaart/CRC

Relates to https://github.com/RobTillaart/Fletcher

Tested on Arduino UNO only.

Interface

Adler class

Use #include "Adler.h"

  • 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

Not tested ESP32 (and many other platforms) yet. First numbers of .add(value) measured with test sketch shows the following timing.

Version Checksum UNO 16 MHz ESP32 240 MHz
0.1.0 Adler32 5.6 us
0.1.2 Adler32 6.6 us

Todo elaborate / investigate.

Performance 2

(since 0.1.2)

The addFast(array, length) is faster than the reference add(array, length) but uses 108 bytes more, so a slightly larger footprint. So depending on your needs, you choose performance or footprint.

See Adler32_performance_addFast.ino

Interface static functions

The function is straightforward.

Use #include "Adler.h"

  • uint32_t adler32(uint8_t *data, uint16_t length) length in units of 1 byte = 8 bits.

The function is typically used for an in memory buffer to calculate the Adler checksum once.

Performance

Not tested extensively, first numbers of .add(array, length) measured with Adler_performance.ino sketch shows the following timing.

Lorem Ipsum text = 868 bytes.

Checksum UNO 16 MHz ESP32 240 MHz
Adler32 1116 us

Average 1116 / 868 = 1.29 us per byte.

Operation

See examples.

Future

  • test other platforms
  • add Adler-16, similar algorithm
    • ADLER16_MOD_PRIME 32749 = largest prime below 2^15 (32768)
    • (0.2.0)