BrowserUk,

I came into this late, but I think using Perl's great 'index' function may give you the desired results. I copied your scripts to get a start, and then used a simple scalar to build the 'Bidirectional lookup' functions. I'm sure they can be improved!

Here goes:

#!/usr/local/bin/myperl

    use strict;
    use warnings;

    use Time::HiRes qw( gettimeofday );
    use Devel::Size qw(total_size);
    my ( $i, %intByStr, %strByInt, $Both );

    $i = 1;
    $intByStr{ $_ } = $i++ for 'aaaa' .. 'zzzz';;

    $strByInt { $intByStr{ $_ } } = $_ for keys %intByStr;;

    print "Hash1: ",total_size( \%intByStr ), "\nHash2: ", total_size(
+ \%strByInt ), "\n";;

    our $ksep = chr(253); our $isep = chr(254);
    foreach my $key ( keys %intByStr )
    {    $Both .= $ksep . $key . $isep . $intByStr{ $key } . "\n";
    }

    print "\$Both: ",length( $Both ), "\n\n";;

    my $testkey = "zabc"; my $testaddr = $intByStr{ $testkey };

    my $stime = gettimeofday;
    my $tkey = get_key( $testaddr );
    print "\tget_key:  ", gettimeofday - $stime, " seconds\n";
    $stime = gettimeofday;
    my $taddr = get_addr( $tkey );
    print "\tget_addr: ", gettimeofday - $stime, " seconds\n";
    print "\t|$tkey|$taddr|\n";
    exit;

sub get_key
{   our( $ksep, $isep );
    my $key = shift; my $result;
    my $si = index( $Both, "$isep$key\n" );
    if ( $si >= 0 )
    {    my $sj = rindex ( $Both, $ksep, $si );
        if ( $sj >= 0 ) { $result = substr( $Both, $sj+1, $si - ($sj+1
+) ); }
    }
    return ( $result );
}

sub get_addr
{   our( $ksep, $isep );
    my $key = shift; my $result;
    my $srch = "$ksep$key$isep"; my $len = length( $srch );
    my $si = index( $Both, "$ksep$key$isep" );
    if ( $si >= 0 )
    {    my $sj = index ( $Both, "\n", $si + $len );
        if ( $sj >= 0 ) { $result = substr( $Both, $si+$len, $sj - ($s
+i+$len) ); }
    }
    return ( $result );
}

1;

__END__

~/tmp:> perl  BUKtest.plx
=========================================================
Hash1: 37741336
Hash2: 43113919
$Both: 5829583
        get_key:  0.00113105773925781 seconds
        get_addr: 0.000988960266113281 seconds
        |zabc|439429|
=========================================================
Actual Time using Linux Debian 'time' command w/perl.5.14.2:
   real    0m1.591s
   user    0m1.560s
   sys     0m0.032s
[download]

Please note the subs return 'undef' if the key or address is not in $Both. Also I would use 'pack' on the address, but that may or may not save space depending on the actual data supplied.

Regards...Ed