From Code to Community: Sponsoring The Perl and Raku Conference 2025 Learn more

SAMYOUNG / EBook-Ishmael-1.06 / lib / EBook / Ishmael / Decode.pm 

            

              
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
—
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95

              
package EBook::Ishmael::Decode;
use 5.016;
our $VERSION = '1.06';
use strict;
use warnings;
use Exporter 'import';
our @EXPORT_OK = qw(lz77_decode);
sub lz77_decode {
        my $encode = shift;
        my $len = length $encode;
        my $p = 0;
        my $decode = '';
        while ($p < $len) {
                my $b = ord substr $encode, $p++, 1;
                # space + xor byte with 0x80
                if ($b >= 0xc0) {
                        $decode .= ' ';
                        $decode .= chr($b ^ 0x80);
                # length-distance pair: get next byte, strip 2 leading bits, split byte
                # into 11 bits of distance and 3 bits of length + 3
                } elsif ($b >= 0x80) {
                        $b = ($b << 8) + ord substr $encode, $p++, 1;
                        my $d = ($b & 0x3fff) >> 3;
                        my $l = ($b & 0x0007) + 3;
                        $decode .= substr $decode, -$d, 1 while $l--;
                # literal copy
                } elsif ($b >= 0x09) {
                        $decode .= chr $b;
                # copy next 1-8 bytes
                } elsif ($b >= 0x01) {
                        $decode .= substr $encode, $p, $b;
                        $p += $b;
                # copy null byte
                } else {
                        $decode .= "\0";
                }
        }
        return $decode;
}
1;
=head1 NAME
EBook::Ishmael::Decode - Ebook decoding routines
=head1 SYNOPSIS
  use App::Ishmael::Decode qw(lz77_decode);
  my $decode = lz77_decode($data);
=head1 DESCRIPTION
B<EBook::Ishmael::Decode> is a module that provides subroutines for decoding
various kinds of encoded ebook text. For L<ishmael> user documentation, you
should consult its manual (this is developer documentation).
=head1 SUBROUTINES
B<EBook::Ishmael::Decode> does not export any subroutines by default.
=head2 $d = lz77_decode($data)
Decodes PalmDoc lz77-encoded C<$data>, returning the decoded data.
=head1 AUTHOR
Written by Samuel Young, E<lt>samyoung12788@gmail.comE<gt>.
This project's source can be found on its
L<Codeberg Page|https://codeberg.org/1-1sam/ishmael>. Comments and pull
requests are welcome!
=head1 COPYRIGHT
Copyright (C) 2025 Samuel Young
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
=cut