110 lines
2.1 KiB
Perl
Executable File
110 lines
2.1 KiB
Perl
Executable File
#!/usr/bin/perl
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#
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# Disassemble a GIF file and display the sections and chunks within.
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#
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# Warning: only part of the specification is implemented.
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#
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use strict;
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use warnings;
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die "Usage: $0 IMAGE\n" unless @ARGV == 1;
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my ($image) = @ARGV;
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open IMAGE, '<', $image or die "$0: open $image: $!\n";
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undef $/;
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my $gif = <IMAGE>;
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close IMAGE;
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print "$image: ", length $gif, " bytes\n\n";
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my @gif = unpack 'C*', $gif;
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my $z = 0;
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output_chunk('Header', 6);
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output_chunk('Logical Screen Descriptor', 7);
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my $global_colors = $gif[10] & 0x80;
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my $color_table_size = 2 << ($gif[10] & 0x07);
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if ($global_colors) {
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output_chunk('Global Color Table', $color_table_size * 3);
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}
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while (1) {
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while ($gif[$z] == 0x21) {
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if ($gif[$z + 1] == 0xf9) {
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output_chunk('Graphic Control Extension', 5 + 2);
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} elsif ($gif[$z + 1] == 0xfe) {
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output_chunk('Comment Extension', 2);
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} elsif ($gif[$z + 1] == 0x01) {
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output_chunk('Plain Text Extension', 13 + 2);
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} elsif ($gif[$z + 1] == 0xff) {
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output_chunk('Application Extension', 12 + 2);
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} else {
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output_chunk((sprintf 'Unknown Extension 0x%.2x',
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$gif[$z + 1]), $gif[$z + 2] + 3);
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}
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while ($gif[$z] != 0) {
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output_chunk('Data Sub-block', $gif[$z] + 1);
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}
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output_chunk('Block Terminator', 1);
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}
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if ($gif[$z] == 0x3b) {
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output_chunk('Trailer', 1);
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last;
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}
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if ($gif[$z] != 0x2c) {
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last;
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}
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output_chunk('Image Descriptor', 10);
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output_chunk('Table Based Image Data', 1);
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while ($gif[$z] != 0) {
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output_chunk('Data Sub-block', $gif[$z] + 1);
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}
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output_chunk('Block Terminator', 1);
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}
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if ($z != @gif) {
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output_chunk('*** Junk on End ***', @gif - $z);
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}
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#
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# Output a chunk of data as hex and characters.
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#
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sub output_chunk
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{
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my ($description, $length) = @_;
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print "$description";
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for (my $i = 0; $i != $length; $i++) {
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if ($i % 8 == 0) {
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print "\n";
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printf "%8i: ", $z + $i;
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}
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if ($z + $i == @gif) {
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print "EOF\n\n";
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print "Unexpected end of file\n";
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exit;
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}
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my $c = $gif[$z + $i];
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printf "%.2x ", $c;
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if (32 <= $c and $c <= 126) {
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printf "'%c'", $c;
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} else {
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print " ";
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}
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print " ";
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}
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print "\n\n";
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$z += $length;
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}
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