Scalar::Vec::Util - Utility routines for vec strings.
VERSION
- Version 0.07
+ Version 0.08
SYNOPSIS
use Scalar::Vec::Util qw<vfill vcopy veq>;
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.
+ vcopy $t, 10, $t, 20, 30; # Overlapping 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 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.
- 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").
+ 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.
+ 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 *
+ 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 $vec, $start, $length, $bit"
- Starting at $start in $vec, fills $length bits with $bit. Grows $vec if
- necessary.
+ "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;
- "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.
+ $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;
- "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.
+ "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;
- "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)".
+ "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;
- "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.
+ $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
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).
+ * 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%
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 :
+ 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 :
+ 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).
+ * 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%
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).
+ * 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%
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).
+ Carp, Exporter (core modules since perl 5), XSLoader (since perl 5.6.0).
SEE ALSO
Bit::Vector gives a complete reimplementation of bit vectors.
<http://www.profvince.com/perl/cover/Scalar-Vec-Util>.
COPYRIGHT & LICENSE
- Copyright 2008,2009,2010,2011,2012 Vincent Pit, all rights reserved.
+ 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.
projects / perl / modules / Scalar-Vec-Util.git / blobdiff