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.
