1 package Scalar::Vec::Util;
10 Scalar::Vec::Util - Utility routines for vec strings.
23 XSLoader::load(__PACKAGE__, $VERSION);
36 use Scalar::Vec::Util qw/vfill vcopy veq/;
39 vfill $s, 0, 100, 1; # Fill with 100 bits 1 starting at 0.
41 vcopy $s, 20, $t, 10, 30; # Copy 30 bits from $s, starting at 20,
42 # to $t, starting at 10.
43 vcopy $t, 10, $t, 20, 30; # Overalapping areas DWIM.
44 if (veq $t, 10, $t, 20, 30) { ... } # Yes, they are equal now.
48 A set of utilities to manipulate bits in vec strings. Highly optimized XS routines are used when available, but straightforward pure perl replacements are also provided for platforms without a C compiler.
50 This module doesn't reimplement bit vectors. It can be used on the very same scalars that C<vec> builds, or actually on any Perl string (C<SVt_PV>).
56 True when pure perl fallbacks are used instead of XS functions.
60 Size in bits of the unit used for moves. The higher this value is, the faster the XS functions are. It's usually C<CHAR_BIT * $Config{alignbytes}>, except on non-little-endian architectures where it currently falls back to C<CHAR_BIT> (e.g. SPARC).
64 =head2 C<vfill $vec, $start, $length, $bit>
66 Starting at C<$start> in C<$vec>, fills C<$length> bits with C<$bit>. Grows C<$vec> if necessary.
71 for (@_) { return 0 unless defined }
76 (undef, my $s, my $l, my $x) = @_;
77 croak "Invalid argument" unless _alldef @_;
80 vec($_[0], $_, 1) = $x for $s .. $s + $l - 1;
83 =head2 C<< vcopy $from => $from_start, $to => $to_start, $length >>
85 Copies C<$length> bits starting at C<$from_start> in C<$from> to C<$to_start> in C<$to>. If C<$from_start + $length> is too long for C<$from>, zeros are copied past C<$length>. Grows C<$to> if necessary.
90 my ($fs, $ts, $l) = @_[1, 3, 4];
91 croak "Invalid argument" unless _alldef @_;
95 vec($_[2], $_ + $step, 1) = vec($_[0], $_, 1) for $fs .. $fs + $l - 1;
96 } else { # There's a risk of overwriting if $_[0] and $_[2] are the same SV.
97 vec($_[2], $_ + $step, 1) = vec($_[0], $_, 1) for reverse $fs .. $fs + $l - 1;
101 =head2 C<< veq $v1 => $v1_start, $v2 => $v2_start, $length >>
103 Returns true if the C<$length> bits starting at C<$v1_start> in C<$v1> and C<$v2_start> in C<$v2> are equal, and false otherwise. If needed, C<$length> is decreased to fit inside C<$v1> and C<$v2> boundaries.
108 my ($s1, $s2, $l) = @_[1, 3, 4];
109 croak "Invalid argument" unless _alldef @_;
112 return 0 if vec($_[0], $s1 + $i, 1) != vec($_[2], $s2 + $i, 1);
120 The functions L</vfill>, L</vcopy> and L</veq> are only exported on request. All of them are exported by the tags C<':funcs'> and C<':all'>.
122 The constants L</SVU_PP> and L</SVU_SIZE> are also only exported on request. They are all exported by the tags C<':consts'> and C<':all'>.
126 use base qw/Exporter/;
130 'funcs' => [ qw/vfill vcopy veq/ ],
131 'consts' => [ qw/SVU_PP SVU_SIZE/ ]
133 our @EXPORT_OK = map { @$_ } values %EXPORT_TAGS;
134 $EXPORT_TAGS{'all'} = [ @EXPORT_OK ];
138 The following timings were obtained by running the C<samples/bench.pl> script with perl 5.8.8 on a Core 2 Duo 2.66GHz machine. The C<_pp> entries are the pure Perl versions, while C<_bv> are L<Bit::Vector> versions.
142 =item Filling bits at a given position :
144 Rate vfill_pp vfill_bv vfill
145 vfill_pp 80.3/s -- -100% -100%
146 vfill_bv 1053399/s 1312401% -- -11%
147 vfill 1180792/s 1471129% 12% --
149 =item Copying bits from a bit vector to a different one :
151 Rate vcopy_pp vcopy_bv vcopy
152 vcopy_pp 112/s -- -100% -100%
153 vcopy_bv 62599/s 55622% -- -89%
154 vcopy 558491/s 497036% 792% --
156 =item Moving bits in the same bit vector from a given position to a different one :
158 Rate vmove_pp vmove_bv vmove
159 vmove_pp 64.8/s -- -100% -100%
160 vmove_bv 64742/s 99751% -- -88%
161 vmove 547980/s 845043% 746% --
163 =item Testing bit equality from different positions of different bit vectors :
165 Rate veq_pp veq_bv veq
166 veq_pp 92.7/s -- -100% -100%
167 veq_bv 32777/s 35241% -- -94%
168 veq 505828/s 545300% 1443% --
174 Please report architectures where we can't use the alignment as the move unit. I'll add exceptions for them.
178 L<Carp>, L<Exporter> (core modules since perl 5), L<XSLoader> (since perl 5.006).
182 L<Bit::Vector> gives a complete reimplementation of bit vectors.
186 Vincent Pit, C<< <perl at profvince.com> >>, L<http://www.profvince.com>.
188 You can contact me by mail or on #perl @ FreeNode (vincent or Prof_Vince).
192 Please report any bugs or feature requests to C<bug-scalar-vec-util at rt.cpan.org>, or through the web interface at L<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.
196 You can find documentation for this module with the perldoc command.
198 perldoc Scalar::Vec::Util
200 Tests code coverage report is available at L<http://www.profvince.com/perl/cover/Scalar-Vec-Util>.
202 =head1 COPYRIGHT & LICENSE
204 Copyright 2008 Vincent Pit, all rights reserved.
206 This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
210 1; # End of Scalar::Vec::Util