NAME

    LCS::BV - Bit Vector (BV) implementation of the Longest Common
    Subsequence (LCS) Algorithm

SYNOPSIS

      use LCS::BV;
    
      $object = LCS::BV->new;
      @lcs    = $object->LCS(\@a,\@b);
    
      $llcs   = $object->LLCS(\@a,\@b);
    
      $positions = $object->prepare(\@a);
      $llcs      = $object->LLCS_prepared($positions,\@b);

ABSTRACT

    LCS::BV implements Algorithm::Diff using bit vectors and is faster in
    most cases, especially on strings with a length shorter than the used
    wordsize of the hardware (32 or 64 bits).

DESCRIPTION

 CONSTRUCTOR

    new()

      Creates a new object which maintains internal storage areas for the
      LCS computation. Use one of these per concurrent LCS() call.

 METHODS

    LLCS(\@a,\@b)

      Return the length of a Longest Common Subsequence, taking two
      arrayrefs as method arguments. It returns an integer.

    LCS(\@a,\@b)

      Finds a Longest Common Subsequence, taking two arrayrefs as method
      arguments. It returns an array reference of corresponding indices,
      which are represented by 2-element array refs.

    prepare(\@a)

      For comparison of the same sequence @a many times against different
      sequences @b it can be faster to prepare @a. It returns a hashref of
      positions. This works only on object mode.

    LLCS_prepared($positions,\@b)

      Return the length of a Longest Common Subsequence, with one side
      prepared. It returns an integer. It is two times faster than LLCS().

 EXPORT

    None by design.

STABILITY

    Until release of version 1.00 the included methods, names of methods
    and their interfaces are subject to change.

    Beginning with version 1.00 the specification will be stable, i.e. not
    changed between major versions.

REFERENCES

    H. Hyyroe. A Note on Bit-Parallel Alignment Computation. In M. Simanek
    and J. Holub, editors, Stringology, pages 79-87. Department of Computer
    Science and Engineering, Faculty of Electrical Engineering, Czech
    Technical University, 2004.

SPEED COMPARISON

        Intel Core i7-4770HQ Processor
        Intel® SSE4.1, Intel® SSE4.2, Intel® AVX2
        4 Cores, 8 Threads
        2.20 - 3.40 GHz
        6 MB Cache
        16 GB DDR3 RAM

    LCS-BV/xt$ perl 50_diff_bench.t

    LCS: Algorithm::Diff, Algorithm::Diff::XS, LCS, LCS::BV

    LCS: [Chrerrplzon] [Choerephon]

                    Rate      LCS:LCS    AD:LCSidx AD:XS:LCSidx   LCS:BV:LCS
    LCS:LCS       9225/s           --         -72%         -87%         -88%
    AD:LCSidx    33185/s         260%           --         -53%         -58%
    AD:XS:LCSidx 70447/s         664%         112%           --         -12%
    LCS:BV:LCS   79644/s         763%         140%          13%           --

    LCS: [qw/a b d/ x 50], [qw/b a d c/ x 50]

                   Rate      LCS:LCS    AD:LCSidx   LCS:BV:LCS AD:XS:LCSidx
    LCS:LCS      49.5/s           --         -37%         -96%         -99%
    AD:LCSidx    79.0/s          60%           --         -94%         -98%
    LCS:BV:LCS   1255/s        2434%        1488%           --         -69%
    AD:XS:LCSidx 4073/s        8124%        5052%         224%           --

    LLCS: [Chrerrplzon] [Choerephon]

                         Rate    LCS:LLCS AD:LCS_length AD:XS:LCS_length LCS:BV:LLCS
    LCS:LLCS          11270/s          --          -70%             -70%        -92%
    AD:LCS_length     37594/s        234%            --              -1%        -75%
    AD:XS:LCS_length  38059/s        238%            1%               --        -74%
    LCS:BV:LLCS      148945/s       1222%          296%             291%          --

    LLCS: [qw/a b d/ x 50], [qw/b a d c/ x 50]

                       Rate     LCS:LLCS AD:LCS_length AD:XS:LCS_length  LCS:BV:LLCS
    LCS:LLCS         50.0/s           --          -37%             -37%         -98%
    AD:LCS_length    79.2/s          58%            --              -1%         -97%
    AD:XS:LCS_length 79.8/s          60%            1%               --         -97%
    LCS:BV:LLCS      2357/s        4614%         2874%            2853%           --

SOURCE REPOSITORY

    http://github.com/wollmers/LCS-BV

SEE ALSO

    Algorithm::Diff LCS LCS::Tiny

AUTHOR

    Helmut Wollmersdorfer <helmut.wollmersdorfer@gmail.com>

COPYRIGHT AND LICENSE

    Copyright 2014-2020 by Helmut Wollmersdorfer

    This library is free software; you can redistribute it and/or modify it
    under the same terms as Perl itself.

