You're right, that's a bug. I think replacing the grep with a one distinguishing between two cases solves it. Here is the updated package:

use strict;
use warnings;

package FastRanges;

sub new($$$) {
    my $class      = shift;
    my $max_length = shift;
    my $ranges_a   = shift;
    my @lookup;
    for ( @{$ranges_a} ) {
        my ( $start, $end ) = @$_;
        my @idx
            = $end >= $start
            ? $start .. $end
            : ( $start .. $max_length, 1 .. $end );
        for my $i (@idx) { $lookup[$i] .= pack 'L', $end }
    }
    bless \@lookup, $class;
}

sub num_ranges_containing($$$) {
    my $self = shift;
    my ( $start, $end ) = @_;    # query range coordinates

    return 0
        unless ( defined $self->[$start] )
        ;    # no ranges overlap the start position of the query

    if ( $end >= $start ) {

        # query range is simple
        # any inverted range in {LOOKUP}[$start] must contain it,
        # and so does any simple range which ends at or after $end
        return 0 + grep { $_ < $start or $end <= $_ } unpack 'L*',
            $self->[$start];
    }
    else {

        # query range is inverted
        # only inverted ranges in {LOOKUP}[$start] which also end
        # at of after $end contain it. simple ranges can't contain
        # the query range
        return 0 + grep { $_ < $start and $end <= $_ } unpack 'L*',
            $self->[$start];
    }
}

1;

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Perhaps this could be done a bit more efficiently, I'm not sure.

Thanks for noting the bug, BrowserUK! I'm sure you saved me a lot of future frustration.

And if you indeed think it now works and also pretty much optimized, I'd be happy to get some ideas for the original question.

In reply to Re^6: Serializing a large object by daverave
in thread Serializing a large object by daverave

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