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133 lines
4.5 KiB
Markdown
133 lines
4.5 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/Soundex/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/Soundex/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/Soundex/blob/master/LICENSE)
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[](https://github.com/RobTillaart/Soundex/releases)
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# Soundex
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Arduino Library for calculating Soundex hash.
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## Description
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This library generates a (string based) hash based upon how a word sounds.
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This algorithm is called Soundex.
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The original algorithm was developed by Robert C. Russell and
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Margaret King Odell over 100 years ago.
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There are several variations of Soundex and these might be supported in the future.
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The algorithm roughly copies the uppercase first letter of the word,
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followed by 3 digits replacing the consonants.
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The base Soundex has 26 x 7 x 7 x 7 = 8918 possible outcomes,
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this could be easily encoded in an uint16_t.
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This insight triggered the experimental functions.
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#### 0.1.2 Experimental
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The library has two experimental functions, **soundex16()** and **soundex32()**.
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These functions pack a Soundex length 5 hash in a uint16_t and a length 10 in a uint32_t.
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These compress soundex() results.
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Advantages (16 bit version):
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- better hash as it adds 1 extra character
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- saves 60% of RAM, (5 bytes vs 2 bytes).
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- allows faster comparisons, (compare 2 bytes is faster than 5 )
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- less storage/communication needed
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- printable as HEX
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Disadvantage:
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- unknown / new.
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- need extra processing.
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The hash codes of these new SoundexNN() are a continuous numeric range.
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| Checksum | bytes | chars | range/values | used | notes |
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|:------------|:-------:|:-------:|---------------:|:-------:|:-------------|
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| soundex | 5 | 4 | 8.917 | 1e-6% | default |
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| soundex16 | 2 | 5 | 62.425 | 95.3% | 0xF3D9 |
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| soundex32 | 4 | 10 | 1.049.193.781 | 24.4% | 0x3E89 6D35 |
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Note that soundex16() and soundex32() compresses info much better than
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the standard soundex().
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A soundex64() is possible and uses 8 bytes.
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It would allow to compress very long soundex() results (up to 22 chars) in 8 bytes.
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#### Links
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- https://en.wikipedia.org/wiki/Soundex
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- https://en.wikipedia.org/wiki/Metaphone (not implemented)
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## Interface
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Use **\#include "Soundex.h"**
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- **Soundex()** Constructor.
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- **void setLength(uint8_t length = 4)** Sets the length to include more digits.
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Maximum length = SOUNDEX_MAX_LENGTH - 1 == 11 (default).
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- **uint8_t getLength()** returns current length.
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- **char \* soundex(const char \* str)** determines the (Russell & Odell) Soundex code of the string.
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- **uint16_t soundex16(const char \* str)** determines the (Russell & Odell) Soundex code with
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length = 5 of the string and packs the result in an uint16_t.
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Note: preferably printed in HEX.
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- **uint32_t soundex32(const char \* str)** determines the (Russell & Odell) Soundex code with
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length == 10 of the string and packs it in an uint32_t.
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Note: preferably printed in HEX.
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#### Performance
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Not tested ESP32 (and many other platforms) yet.
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First numbers of **.soundex("Trichloroethylene")** measured with
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a test sketch shows the following timing per word.
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| Checksum | digits | UNO 16 MHz | ESP32 240 MHz | notes |
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|:----------|:------:|:----------:|:-------------:|:------|
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| soundex | 4 | 28 us | 4 us |
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| soundex16 | 5 | 48 us | 6 us | not optimized
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| soundex32 | 10 | 120 us | 10 us | not optimized
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## Operation
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See examples.
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## Future ideas
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#### must
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- documentation
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- add examples
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#### should
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- more testing
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- other platforms
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- different key lengths
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- string lengths
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- performance
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#### could
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- Other algorithms might be added in the future.
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- reverse_soundex()
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- Daitch–Mokotoff Soundex
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- Beider-Morse Soundex
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- Metaphone
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- use spare bits of soundex16/32 as parity / checksum.
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#### wont
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- efficient storage of the Soundex array
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- encode in nibbles. (13 bytes instead of 26) => more code, performance?
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0x01, 0x23, 0x01 etc.
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(performance test was slower, gain in RAM == PROGMEM loss.
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