Algorithm-Hamming-Perl

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Revision history for Perl extension Algorithm::Hamming::Perl.

0.05  Fri Oct 17 22:43:33 2003
	- original version; created by h2xs 1.21 with options
		-A Algorithm::Hamming::Perl

Perl.pm  view on Meta::CPAN

		} else {
			#
			#  Slow method
			#

			### Fetch the 2 Hamming codes
			$ham_text = unpack("B*",$chars_in);
			$ham_text1 = substr($ham_text,0,12);
			$ham_text2 = substr($ham_text,12);

			### Convert each code into the original byte
			($char_out1,$err) = unhamchar($ham_text1);
			$err_all += $err;
			($char_out2,$err) = unhamchar($ham_text2);
			$err_all += $err;

			### Add bytes to output
			$output .= $char_out1 . $char_out2;
		}
	}

Perl.pm  view on Meta::CPAN

	#  Decode leftover bytes (if present).
	#
	if ($length == ($pos + 2)) {
		### Fetch the 2 leftover bytes
		$chars_in = substr($data,$pos,2);

		### Fetch the Hamming code
		$ham_text = unpack("B*",$chars_in);
		$ham_text1 = substr($ham_text,0,12);
	
		### Convert the code to the original byte
		($char_out1,$err) = unhamchar($ham_text1);
		$err_all += $err;

		### Add byte to output
		$output .= $char_out1;
	}
	
	return ($output,$err_all);
}

Perl.pm  view on Meta::CPAN

=head1 EXPORT SUBROUTINES

=over 4

=item hamming (SCALAR)

Returns the Hamming code from the provided input data.

=item unhamming (SCALAR)

Returns the original data from the provided Hamming code. Single bit errors
are auto corrected.

=item unhamming_err (SCALAR)

Returns the original data from the provided Hamming code, and a number counting
the number of bytes that were corrected. Single bit errors are auto corrected. 

=back

=head1 OTHER SUBROUTINES

=over 4

=item Algorithm::Hamming::Perl::hamming_faster ()

Perl.pm  view on Meta::CPAN

=head1 EXAMPLES

See the example perl programs provided with this module "example*". 
An encoding and decoding example,

   use Algorithm::Hamming::Perl  qw(hamming unhamming);
   
   $data = "Hello";
   $hamcode = hamming($data);

   $original = unhamming($hamcode);

=head1 LIMITATIONS

This is Perl only and can be slow. The Hamming encoding used can only
repair a single bit error within a byte - ie if two bits are damaged within
the one byte then this encoding cannot auto correct the error.

=head1 BUGS

Try not to join Hamming encoded strings together - this may give results

README  view on Meta::CPAN

     data where single bit errors are expected.

     Hamming encoding was invented by Richard Hamming, Bell Labs,
     during 1948.

EXPORT SUBROUTINES
     hamming (SCALAR)
         Returns the Hamming code from the provided input data.

     unhamming (SCALAR)
         Returns the original data from the provided Hamming
         code. Single bit errors are auto corrected.

     unhamming_err (SCALAR)
         Returns the original data from the provided Hamming
         code, and a number counting the number of bytes that
         were corrected. Single bit errors are auto corrected.

OTHER SUBROUTINES
     Algorithm::Hamming::Perl::hamming_faster ()
         This is an optional subroutine that will speed Hamming
         encoding if it is run once at the start of the program.
         It does this by using a larger (hash) cache of
         preprocessed results. The disadvantage is that it uses
         more memory, and can add several seconds to invocation

README  view on Meta::CPAN

EXAMPLES
     See the example perl programs provided with this module
     "example*". An encoding and decoding example,

        use Algorithm::Hamming::Perl  qw(hamming unhamming);

        $data = "Hello";
        $hamcode = hamming($data);

        $original = unhamming($hamcode);


LIMITATIONS
     This is Perl only and can be slow. The Hamming encoding used
     can only repair a single bit error within a byte - ie if two
     bits are damaged within the one byte then this encoding
     cannot auto correct the error.

BUGS
     Try not to join Hamming encoded strings together - this may

example02  view on Meta::CPAN

#!/usr/bin/perl
#
# example02 - example of converting bytes to hamming code, creating 
#		bit errors, then retrieving the original data.
#
# 18-Oct-2003	Brendan Gregg	Created this.

use Algorithm::Hamming::Perl  qw(hamming unhamming unhamming_err);

$data = "Hi";


### Hamming
$hamcode = hamming("$data");