It was pointed out that whilst using 'd' to pack your offsets will work, when it comes to doing the sorting, you would have to unpack the values and do a numeric comparison as sorting numeric data in it's pack'd binary for doesn't work for packed floats/doubles.

Having previously extolled the virtues of sorting numeric data in it's binary form, that doesn't sit right, so here are a couple of routines that will pack and unpack a FP value < 2**53 to an 8-byte binary form that is sortable. along with some rudimentary tests:

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

sub ftob64 {
    return pack 'NN', int( $_[ 0 ] / 2**32 ), int( $_[ 0 ] % 2**32 );
}

sub b64tof {
    my( $hi, $lo ) = unpack 'NN', $_[ 0 ];
    return $hi * 2**32 + $lo;
}

for ( 1 .. 1e6 ) {
    my $test = int( rand 2**53 );
    my $b64 = ftob64 $test;
    my $float = b64tof $b64;
    if( abs( $test - $float ) > 1e-15 ) {
        printf "%31.f v %31.f => diff %31.31f\n", 
            $test, $float, abs( $test - $float );
    }
}

my @randomBin = map{ ftob64 int rand 2**53 } 1 .. 1e6;

my @sortedBin = sort @randomBin;

my @sortedN = map{ b64tof $_ } @sortedBin;

$sortedN[ $_ ] > $sortedN[ $_ + 1 ] 
    and die "Error: $_ : $sortedN[ $_ ] > $sortedN[ $_ + 1 ]"
    for 0 .. $#sortedN - 1;
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