| Subject: | add distance method to count changed bits |
Feature enhancement.
hex_distance(n1, n2) measures the bit distance, as described on
http://ixazon.dynip.com/~cmeclax/nilsimsa.html
A build including this patch can be found in
software.opensuse.org/search?q=perl-Digest-Nilsimsa
| Subject: | hex_distance.patch |
--- Digest-Nilsimsa-0.06/Nilsimsa.pm.orig 2002-06-13 06:15:10.000000000 +0200
+++ Digest-Nilsimsa-0.06/Nilsimsa.pm 2010-06-22 02:07:21.000000000 +0200
@@ -37,6 +37,41 @@ wrapper around nilsimsa implementation i
Pass in any text, any size, and get back a digest string composed 64
hex chars.
+=item $nilsimsa->hex_distance($n1, $n2);
+
+Compare two nilsimsa digests n1 and n1 given as hex chars.
+The return value is a number in the range -128 .. 127, where any value over 24
+(which is 3 sigma) is believed to indicate that the two texts are not generated
+independently.
+
+=cut
+# 773e2df0a02a319ec34a0b71d54029111da90838cbc20ecd3d2d4e18c25a3025
+# 47182cf0802a11dec24a3b75d5042d310ca90838c9d20ecc3d610e98560a3645
+# The nilsimsa of these two codes is 92 on a scale of -128 to +128. That means that
+# 36 bits are different and 220 bits the same. Any nilsimsa over 24 (which is 3
+# sigma) indicates that the two messages are probably not independently
+# generated.
+
+sub hex_distance
+{
+ shift @_ if ref $_[0];
+
+ # 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15
+ my @bit_diff = ( 0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4);
+
+ my @n1 = split //, $_[0];
+ my @n2 = split //, $_[1];
+ die "length differs", if scalar(@n1) != scalar (@n2);
+ my $val = scalar(@n1) * 4;
+ for my $i (0..$#n1)
+ {
+ next if $n1[$i] eq $n2[$i];
+ my ($v1,$v2) = (hex($n1[$i]), hex($n2[$i]));
+ $val -= $bit_diff[$v1 ^ $v2];
+ }
+ return $val - scalar(@n1)*2;
+}
+
=back
=head1 SEE ALSO
--- Digest-Nilsimsa-0.06/t/01-hex_distance.t.orig 2010-06-22 01:33:37.000000000 +0200
+++ Digest-Nilsimsa-0.06/t/01-hex_distance.t 2010-06-22 02:07:51.000000000 +0200
@@ -0,0 +1,19 @@
+#!perl
+use strict;
+use warnings;
+use Test::More tests => 2;
+
+use Digest::Nilsimsa;
+
+my @n = qw(773e2df0a02a319ec34a0b71d54029111da90838cbc20ecd3d2d4e18c25a3025
+ 47182cf0802a11dec24a3b75d5042d310ca90838c9d20ecc3d610e98560a3645);
+
+# from http://ixazon.dynip.com/~cmeclax/nilsimsa.html:
+# The nilsimsa of these two codes is 92 on a scale of -128 to +128. That means
+# that 36 bits are different and 220 bits the same. Any nilsimsa over 24 (which
+# is 3 sigma) indicates that the two messages are probably not independently
+# generated.
+
+cmp_ok(Digest::Nilsimsa::hex_distance(@n), '==', 92, 'hex_distance class method');
+cmp_ok(Digest::Nilsimsa::hex_distance({}, @n), '==', 92, 'hex_distance obj method');
+
--- Digest-Nilsimsa-0.06/MANIFEST.orig 2002-05-21 00:07:21.000000000 +0200
+++ Digest-Nilsimsa-0.06/MANIFEST 2010-06-22 02:09:12.000000000 +0200
@@ -7,6 +7,7 @@ README
_nilsimsa.c
nilsimsa.h
t/00_load.t
+t/01-hex_distance.t
t/a.txt
t/b.txt
t/d.txt