Reversing chunks in a string (bits of byte in a bitstring)

spurperl has asked for the wisdom of the Perl Monks concerning the following question:

Hi all,

I have a string of 0s and 1s, for instance "1101000010101111". I want to reverse each group of 8 chars in it. For the above example: "0000101111110101"

The application is a string of bits, and the bits of each byte must be reversed.

I'm looking for the fastest way to achieve this, on strings of small length (up to a few hundred chars). The obvius solution, which is pretty fast is with substr() on each 8 bits (in a for loop). Any better ideas ?

Thanks in advance

Comment on Reversing chunks in a string (bits of byte in a bitstring)

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Re: Reversing chunks in a string (bits of byte in a bitstring) by broquaint (Abbot) on Feb 16, 2004 at 14:28 UTC
This should be quite nippy. `my $str = '1234567812345678'; $str =~ s/(.{8})/reverse $1/eg; print "str: $str\n"; __output__ str: 8765432187654321` [download] HTH `_________ broquaint`	[reply] [d/l]
Re: Reversing chunks in a string (bits of byte in a bitstring) by Tomte (Priest) on Feb 16, 2004 at 14:52 UTC
I'd consider Bit::Vector to ensure a (supposed :) best combination of speed and platform-independence, not to mention ease of use: `use Bit::Vector; my $size=16; my $bits = Bit::Vector->new_Bin($size,"1101000010101111"); print "orig:\t\t",$bits->to_Bin(), "\n"; $bits->Interval_Reverse(($_-1)8,$_8-1) for (1..($size/8)); print "byte-rev:\t",$bits->to_Bin(), "\n"; __END__ orig: 1101000010101111 byte-rev: 0000101111110101` [download] regards, tomte Hlade's Law: If you have a difficult task, give it to a lazy person -- they will find an easier way to do it.	[reply] [d/l]
Re: Reversing chunks in a string (bits of byte in a bitstring) by belg4mit (Prior) on Feb 16, 2004 at 14:36 UTC
I should think the obvious implementation would be to use pack and unpack with a combination of little-endian and big-endian templates. `-- I'm not belgian but I play one on TV.`	[reply]
Re: Reversing chunks in a string (bits of byte in a bitstring) by jmcnamara (Monsignor) on Feb 16, 2004 at 20:07 UTC
Here is one way. `#!/usr/bin/perl -wl my $str1 = "1101000010101111"; my $str2 = join "", unpack "b8b8", pack "B*", $str1; print for $str1, $str2; __END__ Prints: 1101000010101111 0000101111110101` [download] For this sort of task pack is usually the fastest method but to be sure you should benchmark it against the other solutions. -- John.	[reply] [d/l]