Challenge 015 task 2

1 files changed, 66 insertions, 0 deletions

diff --git a/challenge-015/jo-37/perl/ch-2.pl b/challenge-015/jo-37/perl/ch-2.pl
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+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0 '!float';
+use PDL;
+use experimental 'signatures';
+
+our ($tests, $examples, $decrypt, $key);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV == 1 && $key;
+usage: $0 -key=KEY [-decrypt] TEXT
+
+-key=KEY
+    use KEY for en-/decryption
+
+-decrypt
+    decrypt TEXT. (Default: encrypt)
+
+TEXT
+    en- or decrypt TEXT
+
+EOS
+
+
+### Input and Output
+
+say vigenere($key, shift, !$decrypt);
+
+
+### Implementation
+
+sub vigenere ($key, $text, $enc) {
+    # Convert the lowercase text to offsets from 'a'.
+    my $t = byte map ord() - ord('a'), split //, lc $text;
+    # Convert the lowercase key to offsets from 'a' and periodically
+    # extend it to text's length.
+    my $k = byte(map ord() - ord('a'), split //, lc $key)
+        ->range(0, $t->dim(0), 'p');
+
+    # Add or substract text and key, take the result mod 26 and convert
+    # back to characters.
+    join '', map chr($_ + ord('a')), (($t + (-1)**!$enc * $k) % 26)->list;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is vigenere('lemon', 'attackatdawn', 1), 'lxfopvefrnhr',
+            'encoding example from Wiki';
+        is vigenere('lemon', 'lxfopvefrnhr', 0), 'attackatdawn',
+            'decoding example from Wiki';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+	}
+
+    done_testing;
+    exit;
+}