#!/usr/bin/perl -w
# $Id: swap_endian,v 1.8 2004/04/23 16:29:45 braup Exp $
# Copyright 2004 Bruce Raup  (http://cires.colorado.edu/~braup/)
# This software is distributed under the GNU General Public License.  See
# http://www.gnu.org/licenses/gpl.txt for the text of this license.
# In short:
#    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 2 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.

$| = 1;

($progname = $0)        =~ s!^.*/!!;  # get basename of program

use Getopt::Std;

$version = '$Revision: 1.8 $';
($version) = $version =~ /^\$Revision:\s*(\d+\.\d*)/;

# Defaults
$bytes = 4;  # number of bytes to swap

$usage = "$progname version $version

Program to swap bytes (endianness).

Usage:
  $progname  -h            (prints this help message and exits)
OR
  $progname  [-q] [-bNum] infile outfile
where
  -b    specifies Num bytes to swap [default:  $bytes]
  -q    specifies quiet mode

Examples:
  swap_endian -b2 little big
  gzip -dc little.gz | swap_endian -b2 - - | gzip -c > big.gz
";

$opt_q = $opt_h = $opt_b = '';
if (! getopts('hqb:') ) {
  die "$usage\n";
}

warn "$progname version $version\n" unless $opt_q;

die "$usage\n" if $opt_h;

die "$usage\n" if @ARGV != 2;

$bytes = $opt_b if $opt_b;

($infile, $outfile) = @ARGV;

if (-e $outfile) {
  warn "$outfile already exists.  Overwrite?  ";
  $answer = <STDIN>;
  unless ($answer =~ /^y/i) {
    warn "Okay, we'll abort then.  Exiting.\n";
    exit 1;
  }
}

warn "Opening files ... " unless $opt_q;
open IN,  "$infile"  or die "Couldn't open $infile for reading $!";
open OUT, ">$outfile" or die "Couldn't open $outfile for writing $!";
warn "Done.\nStarting to swap, $bytes bytes at a time ... " unless $opt_q;

$template = 'c' x $bytes;
while (read IN, $in, $bytes) {
  $out = pack( $template, reverse( unpack( $template, $in ) ) );
  print OUT $out;
}
close IN;
close OUT;
warn "Done.\n" unless $opt_q;