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