NAME
Scalar::Vec::Util - Utility routines for vec strings.
VERSION
Version 0.07
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; # Overalapping areas DWIM.
if (veq $t, 10, $t, 20, 30) { ... } # Yes, they are equal now.DESCRIPTION
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.
This module doesn't reimplement bit vectors. It can be used on the very same scalars that vec builds, or actually on any Perl string (SVt_PV).
CONSTANTS
SVU_PP
True when pure perl fallbacks are used instead of XS functions.
SVU_SIZE
Size in bits of the unit used for moves. The higher this value is, the faster the XS functions are. It's usually CHAR_BIT * $Config{alignbytes}, except on non-little-endian architectures where it currently falls back to CHAR_BIT (e.g. SPARC).
FUNCTIONS
vfill $vec, $start, $length, $bit
Starting at $start in $vec, fills $length bits with $bit. Grows $vec if necessary.
vcopy $from => $from_start, $to => $to_start, $length
Copies $length bits starting at $from_start in $from to $to_start in $to. If $from_start + $length is too long for $from, zeros are copied past $length. Grows $to if necessary. Doesn't need to allocate any extra memory.
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. If $insert is defined, also fills the resulting gap with ones if $insert is true and zeros if it's false. Bits outside of the specified area are left untouched. Doesn't need to allocate any extra memory.
vrot $v, $start, $length, $bits
In the area starting at $start and of length $length in $v, rotates bits abs $bits positions left if $bits > 0 and right otherwise. Bits outside of the specified area are left untouched. Currently allocates an extra buffer of size O($bits).
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. If needed, $length is decreased to fit inside $v1 and $v2 boundaries.
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 5.006).
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::UtilTests code coverage report is available at http://www.profvince.com/perl/cover/Scalar-Vec-Util.
COPYRIGHT & LICENSE
Copyright 2008,2009,2010,2011,2012 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.