#! perl -slw
use strict;
use Math::Random::MT qw[ rand ];
use Benchmark::Timer;

our $N ||= 1_000_000;

{
    ## Use closures to retain info between calls or make it an object.
    my( $filename, $fh, $len ) = 'uniqints.dat';
    sub uniqPersistant {
        my( $no ) = @_;
        unless( $fh ) {
            ## Open an existing (or new first time) file;
            my $mode = -e( $filename ) ? '+<:raw' : '+>:raw';
            open $fh, $mode, $filename 
                or die "$filename ($mode) : $!";
            ## Remember the length.
            $len = -s $filename;
        }
        ## Calculate byte offset and bit
        my( $oByte, $bit ) = ( int( $no / 8 ), ( $no % 8 ) );

        ## Extend the file with nulls if writing a new highest value
        if( $len < $oByte ) {
            my $extend = ( $oByte - $len + 1 );
            sysseek $fh, 0, 2;
            syswrite $fh, chr(0) x $extend;
            $len += $extend; ## Accumulate the extension
        }

        ## Read the byte
        my $byte;
        sysseek $fh, $oByte, 0;
        sysread $fh, $byte, 1;
        ## All done if the bit is set
        return 1 if vec $byte, $bit, 1;
        
        ## Otherwise set it, re-write teh byte and return false;
        vec( $byte, $bit, 1 ) = 1;
        sysseek $fh, $oByte, 0;
        syswrite $fh, $byte, 1;
        return;
    }
}

my @numbers = map{ int rand 1_000_000 } 1 .. $N;

my $T = new Benchmark::Timer;
for ( 1 .. 2 ) {
    my $count = 0;
    $T->start( "Pass $_" );
    uniqPersistant( $_ ) or $count++ for @numbers;
    $T->stop( "Pass $_" );
    print "During pass $_; $count numbers uniq numbers were previously
+ unset";
}

$T->report;
__END__
P:\test>429615
During pass 1; 632091 numbers uniq numbers were previously unset
During pass 2; 0 numbers uniq numbers were previously unset
  1 trial  of Pass 1 (  11.891s total), 11.891s/trial

  1 trial  of Pass 2 (   6.469s total), 6.469s/trial


P:\test>dir uniqints.dat
 Volume in drive P has no label.
 Volume Serial Number is BCCA-B4CC

 Directory of P:\test

10/02/2005  11:17           125,000 uniqints.dat
               1 File(s)        125,000 bytes
               0 Dir(s)  58,981,855,232 bytes free
[download]