#! /usr/bin/perl

use autodie;

(my $prog = $0) =~ s!^.*/!!;

die "usage: $prog ORIG COPY\n" unless @ARGV == 2;
my ($orig, $copy) = @ARGV;

open my $ofh, "<", $orig; binmode $ofh;
open my $cfh, "<", $copy; binmode $cfh;

my $SECSZ = 2048;
my $ZERO = "\0" x $SECSZ;

my $rc = 0;
sub bad ($) {
  my ($msg) = @_;
  print STDERR "$prog: $msg\n";
  $rc = 2 unless $rc > 2;
}

my ($obuf, $cbuf);
my $i = 0;
my $report = "";
my $prev = undef;
my $st = undef;
sub update ($) {
  my ($newst) = @_;
  if ($newst ne $st) {
    if (defined $st) {
      $report .= ", " if $report;
      if ($st eq 'copy') { $report .= "$prev .. $i"; }
      elsif ($st eq 'zero') { $report .= "[$prev .. $i]"; }
      else { $report .= "($st: $prev .. $i)"; }
    }
    $st = $newst; $prev = $i;
  }
}
SECTOR: for (;;) {
  my $on = read $ofh, $obuf, $SECSZ;
  my $cn = read $cfh, $cbuf, $SECSZ;
  if ($on < $SECSZ || $cn < $SECSZ) {
    if ($on == $SECSZ) {
      if (!$cn) { bad "premature end at sector #$i in `$copy'"; }
      else { bad "short sector #$i in `$copy'"; }
    } elsif (!on) {
      bad "continuation from sector #$i in `$copy'";
    } elsif ($on == $cn) {
      bad "final short sector #$i in both files" if $on;
      if ($cbuf eq $obuf) { $newst = 'copy'; }
      elsif ($cbuf eq "\0" x $on) { $newst = 'zero'; }
      else { bad "corrupted short sector #$i in `$copy'"; }
    } else {
      bad "short sector #$i in both files"
    }
    last SECTOR;
  }

  my $newst;
  if ($cbuf eq $obuf) { $newst = 'copy'; }
  elsif ($cbuf eq $ZERO) { $newst = 'zero'; }
  else { $newst = 'bogus'; }
  update $newst; $i++;
}
update 'end';
print $report, "\n";
exit $rc;