Vincent Pit

NAME

Scalar::Vec::Util - Utility routines for vec strings.

VERSION

Version 0.08

SYNOPSIS

    use Scalar::Vec::Util qw<vfill vcopy veq>;

    my $s;
    vfill $s, 0, 100, 1; # Fill with 100 bits 1 starting at 0.
    my $t;
    vcopy $s, 20, $t, 10, 30; # Copy 30 bits from $s, starting at 20,
                              #                to $t, starting at 10.
    vcopy $t, 10, $t, 20, 30; # Overlapping areas DWIM.
    if (veq $t, 10, $t, 20, 30) { ... } # Yes, they are equal now.

DESCRIPTION

This module provides a set of utility routines that efficiently manipulate bits in vec strings. Highly optimized XS functions are used whenever possible, but straightforward pure Perl replacements are also available for platforms without a C compiler.

Note that this module does not aim at reimplementing bit vectors : all its functions can be used on any Perl string, just like "vec" in perlfunc.

CONSTANTS

SVU_PP

True when pure Perl fallbacks are used instead of XS functions.

SVU_SIZE

The size (in bits) of the unit used for bit operations. The higher this value is, the faster the XS functions are. It is usually CHAR_BIT * $Config{alignbytes}, except on non-little-endian architectures where it currently falls back to CHAR_BIT (e.g. SPARC).

FUNCTIONS

vfill

    vfill $vec, $start, $length, $bit;

Starting at $start in $vec, fills $length bits with ones if $bit is true and with zeros if $bit is false.

$vec is upgraded to a string and extended if necessary. Bits that are outside of the specified area are left untouched.

vcopy

    vcopy $from => $from_start, $to => $to_start, $length;

Copies $length bits starting at $from_start in $from to $to_start in $to.

$from and $to are allowed to be the same scalar, and the given areas can rightfully overlap.

$from is upgraded to a string if it isn't one already. If $from_start + $length goes out of the bounds of $from, then the extra bits are treated as zeros. $to is upgraded to a string and extended if necessary. The content of $from is not modified, except when it is equal to $to. Bits that are outside of the specified area are left untouched.

This function does not need to allocate any extra memory.

vshift

    vshift $v, $start, $length => $bits, $insert;

In the area starting at $start and of length $length in $v, shift bits abs $bits positions left if $bits > 0 and right otherwise.

When $insert is defined, the resulting gap is also filled with ones if $insert is true and with zeros if $insert is false.

$v is upgraded to a string if it isn't one already. If $start + $length goes out of the bounds of $v, then the extra bits are treated as zeros. Bits that are outside of the specified area are left untouched.

This function does not need to allocate any extra memory.

vrot

    vrot $v, $start, $length, $bits;

In the area starting at $start and of length $length in $v, rotates bits abs $bits positions left if $bits > 0 and right otherwise.

$v is upgraded to a string if it isn't one already. If $start + $length goes out of the bounds of $v, then the extra bits are treated as zeros. Bits that are outside of the specified area are left untouched.

This function currently allocates an extra buffer of size O($bits).

veq

    veq $v1 => $v1_start, $v2 => $v2_start, $length;

Returns true if the $length bits starting at $v1_start in $v1 and $v2_start in $v2 are equal, and false otherwise.

$v1 and $v2 are upgraded to strings if they aren't already, but their contents are never modified. If $v1_start + $length (respectively $v2_start + $length) goes out of the bounds of $v1 (respectively $v2), then the extra bits are treated as zeros.

This function does not need to allocate any extra memory.

EXPORT

The functions "vfill", "vcopy", "vshift", "vrot" and "veq" are only exported on request. All of them are exported by the tags ':funcs' and ':all'.

The constants "SVU_PP" and "SVU_SIZE" are also only exported on request. They are all exported by the tags ':consts' and ':all'.

BENCHMARKS

The following timings were obtained by running the samples/bench.pl script. The _pp entries are the pure Perl versions, whereas _bv are Bit::Vector versions.

  • This is for perl 5.8.8 on a Core 2 Duo 2.66GHz machine (unit is 64 bits).

        Filling bits at a given position :
                      Rate vfill_pp vfill_bv    vfill
        vfill_pp    80.3/s       --    -100%    -100%
        vfill_bv 1053399/s 1312401%       --     -11%
        vfill    1180792/s 1471129%      12%       --
    
        Copying bits from a bit vector to a different one :
                     Rate vcopy_pp vcopy_bv    vcopy
        vcopy_pp    112/s       --    -100%    -100%
        vcopy_bv  62599/s   55622%       --     -89%
        vcopy    558491/s  497036%     792%       --
    
        Moving bits in the same bit vector from a given position
        to a different one :
                     Rate vmove_pp vmove_bv    vmove
        vmove_pp   64.8/s       --    -100%    -100%
        vmove_bv  64742/s   99751%       --     -88%
        vmove    547980/s  845043%     746%       --
    
        Testing bit equality from different positions of different
        bit vectors :
                   Rate  veq_pp  veq_bv     veq
        veq_pp   92.7/s      --   -100%   -100%
        veq_bv  32777/s  35241%      --    -94%
        veq    505828/s 545300%   1443%      --
  • This is for perl 5.10.0 on a Pentium 4 3.0GHz (unit is 32 bits).

                     Rate vfill_pp vfill_bv    vfill
        vfill_pp    185/s       --    -100%    -100%
        vfill_bv 407979/s  220068%       --     -16%
        vfill    486022/s  262184%      19%       --
    
                     Rate vcopy_pp vcopy_bv    vcopy
        vcopy_pp   61.5/s       --    -100%    -100%
        vcopy_bv  32548/s   52853%       --     -83%
        vcopy    187360/s  304724%     476%       --
    
                     Rate vmove_pp vmove_bv    vmove
        vmove_pp   63.1/s       --    -100%    -100%
        vmove_bv  32829/s   51933%       --     -83%
        vmove    188572/s  298787%     474%       --
    
                   Rate  veq_pp  veq_bv     veq
        veq_pp   34.2/s      --   -100%   -100%
        veq_bv  17518/s  51190%      --    -91%
        veq    192181/s 562591%    997%      --
  • This is for perl 5.10.0 on an UltraSPARC-IIi (unit is 8 bits).

                    Rate vfill_pp    vfill vfill_bv
        vfill_pp  4.23/s       --    -100%    -100%
        vfill    30039/s  709283%       --     -17%
        vfill_bv 36022/s  850568%      20%       --
    
                    Rate vcopy_pp vcopy_bv    vcopy
        vcopy_pp  2.74/s       --    -100%    -100%
        vcopy_bv  8146/s  297694%       --     -60%
        vcopy    20266/s  740740%     149%       --
    
                    Rate vmove_pp vmove_bv    vmove
        vmove_pp  2.66/s       --    -100%    -100%
        vmove_bv  8274/s  311196%       --     -59%
        vmove    20287/s  763190%     145%       --
    
                  Rate  veq_pp  veq_bv     veq
        veq_pp  7.33/s      --   -100%   -100%
        veq_bv  2499/s  33978%      --    -87%
        veq    19675/s 268193%    687%      --

CAVEATS

Please report architectures where we can't use the alignment as the move unit. I'll add exceptions for them.

DEPENDENCIES

perl 5.6.

A C compiler. This module may happen to build with a C++ compiler as well, but don't rely on it, as no guarantee is made in this regard.

Carp, Exporter (core modules since perl 5), XSLoader (since perl 5.6.0).

SEE ALSO

Bit::Vector gives a complete reimplementation of bit vectors.

AUTHOR

Vincent Pit, <perl at profvince.com>, http://www.profvince.com.

You can contact me by mail or on irc.perl.org (vincent).

BUGS

Please report any bugs or feature requests to bug-scalar-vec-util at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Scalar-Vec-Util. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

SUPPORT

You can find documentation for this module with the perldoc command.

    perldoc Scalar::Vec::Util

Tests code coverage report is available at http://www.profvince.com/perl/cover/Scalar-Vec-Util.

COPYRIGHT & LICENSE

Copyright 2008,2009,2010,2011,2012,2013 Vincent Pit, all rights reserved.

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