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81 lines
2.7 KiB
Markdown
81 lines
2.7 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/LUHN/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/LUHN/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/LUHN/blob/master/LICENSE)
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[](https://github.com/RobTillaart/LUHN/releases)
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# LUHN
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Arduino Library for calculating LUHN checksum.
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## Description
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The LUHN algorithm is a checksum (a.k.a. mod 10) invented by **Hans Peter Luhn** in 1960.
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It is used to validate a variety of product ID's to detect typing errors an/of digit swaps.
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So it is not to secure a number but to prevent common mistakes when entering a code in a system.
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The LUHN check uses very few resources and is pretty fast.
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Basic idea is to put all digits-1 through the formula and the output should equal the last digit.
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Note: some LUHN validations uses the reversed product string.
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- https://en.wikipedia.org/wiki/Luhn_algorithm
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#### related
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- https://github.com/RobTillaart/Adler
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- https://github.com/RobTillaart/CRC
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- https://github.com/RobTillaart/Fletcher
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- https://github.com/RobTillaart/LUHN
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## Interface
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```cpp
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#include "LUHN.h"
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```
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- **LUHN()** constructor
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- **bool isValid(char \* buffer )** validates the code in the parameter buffer.
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The parameter buffer is a '\0' terminated char array. Length should be less than 254.
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- **bool isValid(const char \* buffer )** idem.
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- **char generateChecksum(char \* buffer)**
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Returns the char '0'..'9' which is the checksum of the code in the parameter buffer.
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The parameter buffer is a '\0' terminated char array. Length should be less than 254.
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- **bool generate(char \* buffer, uint8_t length, char \* prefix)**
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Generates a char array including LUHN number with a defined prefix of max length.
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Returns false if the prefix exceeds length -1.
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#### Stream
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- **char add(char c)** add char, return LUHN so far.
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- **char reset()** return last LUHN.
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The internal counter for the stream interface is 16 bit.
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This limits the nr of add() calls to about 65530.
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(if this is a problem, make it an uinit32_t)
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## Future
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#### must
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- update documentation
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#### should
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- unit tests
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- look for optimization
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#### could
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- uint32_t interface for up to 8 digit ID's (99.999.999)
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- **isValid(uint32_t)**
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- **generateChecksum(uint32_t)**
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- how about leading zero's
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