#!/usr/bin/env perl
#
# Dump a binary PDP-7 file where a word is encoded as three bytes,
# with sixbits are stored big-endian in each of the three byte.
#
use strict;
use warnings;

die("Usage: $0 binaryfile\n") if (@ARGV==0);

open(my $IN, "<", $ARGV[0]) || die("Can't open $ARGV[0]: $!\n");
while (1) {
  # Convert three bytes into one 18-bit word
  my $result= read($IN, my $three, 3);
  last if ($result != 3);       # Not enough bytes read
  my ($b1, $b2, $b3)= unpack("CCC", $three);
  my $word= (($b1 & 077) << 12) | (($b2 & 077) << 6) | ($b3 & 077);

  my $c1= ($word >> 9) & 0777;
  $c1= (($c1 >= 32) && ($c1 <= 126)) ? chr($c1) : ' ';
  my $c2= $word & 0777;
  $c2= (($c2 >= 32) && ($c2 <= 126)) ? chr($c2) : ' ';
  printf("%06o %s%s\n", $word, $c1, $c2)
}
close($IN);
exit(0);