https://github.com/palestamp/hamming_distance

Hamming distance extension for Postgres.
https://github.com/palestamp/hamming_distance

c hamming-distance pgsql postgresql

Last synced: 4 months ago
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Hamming distance extension for Postgres.

• Host: GitHub
• URL: https://github.com/palestamp/hamming_distance
• Owner: palestamp
• License: mit
• Created: 2016-08-23T11:59:08.000Z (over 9 years ago)
• Default Branch: master
• Last Pushed: 2017-07-04T22:26:36.000Z (over 8 years ago)
• Last Synced: 2025-02-01T02:41:22.791Z (about 1 year ago)
• Topics: c, hamming-distance, pgsql, postgresql
• Language: C
• Homepage:
• Size: 4.88 KB
• Stars: 6
• Watchers: 2
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

          
Hex-Pair Hamming Distance Functions

===================================

This extension provides four functions to work with hex representation of 

feature vector.

    

Every function asserts that both arguments have the same length.

### hamming_distance(varchar, varchar) RETURNS int (IMMUTABLE STRICT)

Computes absolute hamming distance between to FVs

    SELECT hamming_distance('1d3f', '1110');

     hamming_distance

    ------------------

                    7

    (1 row)

This expands as

    a = '1d3f'  -> 0001 1101 0011 1111

    b = '1110'  -> 0001 0001 0001 0000

 

    c = a ^ b   -> 0000 1100 0010 1111

    popcount(c) ->   0 + 2 + 1 + 4 = 7

    

### hamming_similarity(varchar, varchar) RETURNS int (IMMUTABLE STRICT)

    SELECT hamming_similarity('1d3f', '1110');

     hamming_similarity

    --------------------

                      9

    (1 row)

Can be defined as

    

    HAMMING_SIMILARITY = len(a) * 4 - hamming_distance(a, b);

### hamming_distance_normalized(varchar, varchar) RETURNS float (IMMUTABLE STRICT)

    SELECT hamming_distance_normalized('1d3f', '1110');

     hamming_distance_normalized

    -----------------------------

                          0.4375

    (1 row)

Can be defined as

    

    HAMMING_DISTANCE_NORM = hamming_distance(a, b) / len(a) * 4;

### hamming_similarity_normalized(varchar, varchar) RETURNS float (IMMUTABLE STRICT)

    SELECT hamming_similarity_normalized('1d3f', '1110');

     hamming_similarity_normalized

    -------------------------------

                            0.5625

    (1 row)

Can be defined as

    

    HAMMING_SIMILARITY_NORM = hamming_similarity(a, b) / len(a) * 4;

Installation

============

    cd .../hamming_distance

    sudo make install

Running tests

=============

    

    make installcheck