#!/usr/bin/perl

#
# bit_checker
#
# Checks to make sure the file only contains valid bits.
# Only values of 0 and 1 are considered valid for bits.
#
# usage: bit_checker [<file> [...] ]
# 
# Exit code 0 if no errors.
# Nonzero exit code on error.
#
# Assumes an 8-bit per byte system
#
# Inspired by http://thedailywtf.com/Articles/Some-Crazy-Reason.aspx
#

use strict;
use warnings;


sub process {
   my ($fh, $name) = @_;

   my $error  = 0;
   my $offset = 0;

   local $/ = \(64*1024);
   while (my $blk = <$fh>) {

      for my $byte_idx ( 0 .. length($blk)-1 ) {
         my $byte = ord(substr($blk, $byte_idx, 1));

         for my $bit_idx ( reverse 0 .. 7 ) {
            my $bit = ( $byte >> $bit_idx ) & 1;

            if ($bit != 0 && $bit != 1) {
               $error = 1;
               warn("Found bad bit ($bit) in $name"
                   ." at pos ".( $offset+$byte_idx ).":$bit_idx"
                   .\n");
            }
         }
      }

      $offset += length($blk);
   }

   return $error;
}


{
   my $error = 0;

   if (@ARGV) {
      for my $qfn (@ARGV) {
         # Raw stream without disabling buffering.
         open(my $fh, '<:unix:perlio', $qfn)
            or die("Can't open \"$qfn\": $!\n");
         $error = process($fh, "file \"$qfn\"") || $error;
      }
   } else {
      binmode(*STDIN);
      $error = process(*STDIN, 'STDIN');
   }

   exit($error);
}
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