From 747bc1c1f749e073e3681d85354f6fd490db07ea Mon Sep 17 00:00:00 2001
From: trizen <trizenx@tutanota.com>
Date: Sat, 9 Nov 2024 15:51:00 +0200
Subject: [PATCH] new file:   Encoding/swap_transform.pl

---
 Encoding/swap_transform.pl | 91 ++++++++++++++++++++++++++++++++++++++
 README.md                  |  1 +
 2 files changed, 92 insertions(+)
 create mode 100644 Encoding/swap_transform.pl

diff --git a/Encoding/swap_transform.pl b/Encoding/swap_transform.pl
new file mode 100644
index 00000000..7706a951
--- /dev/null
+++ b/Encoding/swap_transform.pl
@@ -0,0 +1,91 @@
+#!/usr/bin/perl
+
+# Author: Daniel "Trizen" Șuteu
+# Date: 09 November 2024
+# https://github.com/trizen
+
+# A reversible transform, based on swapping of elements.
+
+use 5.036;
+
+sub swap_transform ($text, $extra = 1) {
+
+    my @bits;
+    my @arr = unpack('C*', $text);
+    my $k   = 0;
+
+    foreach my $i (1 .. $#arr) {
+        if ($arr[$i] < $arr[$i - 1 - $k]) {
+            push @bits, 1;
+            unshift @arr, splice(@arr, $i, 1);
+            ++$k if $extra;
+        }
+        else {
+            push @bits, 0;
+        }
+    }
+
+    return (pack('C*', @arr), \@bits);
+}
+
+sub reverse_swap_transform ($text, $bits) {
+    my @arr = unpack('C*', $text);
+
+    for (my $i = $#arr ; $i >= 0 ; --$i) {
+        if ($bits->[$i - 1] == 1) {
+            splice(@arr, $i, 0, shift(@arr));
+        }
+    }
+
+    pack('C*', @arr);
+}
+
+foreach my $text (
+    "TOBEORNOTTOBEORTOBEORNOT",
+    "abracadabra",
+    "DABDDBBDDBA",
+    "CoMpReSSeD",
+    "AM SAM. I AM SAM. SAM I AM. THAT SAM-I-AM",
+    do {
+        open my $fh, '<:raw', __FILE__;
+        local $/;
+        <$fh>;
+    }
+  ) {
+
+    my ($t, $bits) = swap_transform($text);
+    my $rev = reverse_swap_transform($t, $bits);
+
+    if (length($t) < 100) {
+        say $t;
+        say join('', @$bits);
+        say $rev;
+        say '-' x 80;
+    }
+
+    if ($rev ne $text) {
+        die "Failed for: $text";
+    }
+}
+
+__END__
+NEBOBNRBOTEOOTTOEORTOROT
+11001100001000011100100
+TOBEORNOTTOBEORTOBEORNOT
+--------------------------------------------------------------------------------
+aaaaabrcdbr
+0010101001
+abracadabra
+--------------------------------------------------------------------------------
+ABADBDDBDDB
+1000100001
+DABDDBBDDBA
+--------------------------------------------------------------------------------
+eSRMCopeSD
+010101010
+CoMpReSSeD
+--------------------------------------------------------------------------------
+--A A . I  .A   .A AMSMIAMSMSAMAMTHTSMIAM
+0101011010010101100011100110010101010100
+AM SAM. I AM SAM. SAM I AM. THAT SAM-I-AM
+--------------------------------------------------------------------------------
diff --git a/README.md b/README.md
index 8c9370e7..def54f6b 100644
--- a/README.md
+++ b/README.md
@@ -284,6 +284,7 @@ A nice collection of day-to-day Perl scripts.
     * [RANS encoding mpz](./Encoding/rANS_encoding_mpz.pl)
     * [Run length with elias coding](./Encoding/run_length_with_elias_coding.pl)
     * [String to integer encoding based on primes](./Encoding/string_to_integer_encoding_based_on_primes.pl)
+    * [Swap transform](./Encoding/swap_transform.pl)
     * [Tlen encoding](./Encoding/tlen_encoding.pl)
     * [Variable length run encoding](./Encoding/variable_length_run_encoding.pl)
 * Encryption