Another binary chop solution

#! perl -slw
use vars qw[$MAX $SIZE $LO $HI];
use strict;

$MAX  ||= 100;
$SIZE ||= 10;
$LO    ||= 25;
$HI   ||= 50;

sub bsearch {
    my ($ref, $val) = @_;
    my ($lo, $hi) = (0, $#$ref);

    while ($lo < $hi) {
        my $i = ($lo+$hi)>>1;
        my $bool = $val <=> $ref->[$i];
           if ($bool < 0) { $hi = $i;     }
        elsif ($bool > 0) { $lo = $i + 1; }
        else              { return $i;    }
    }
    return $hi;
}

sub range {
    my ($ref, $lo, $hi) = @_;
    my $lidx = bsearch($ref, $lo);
    $lo = ($ref->[$lidx] > $lo and $lidx > 0)    ? $ref->[--$lidx] : $
+ref->[$lidx];
    my $hidx = bsearch($ref, $hi);
    $hi = ($ref->[$hidx] < $hi and $hi < $#$ref) ? $ref->[$hidx++] : $
+ref->[$hidx];
    $lo .. $hi;
}

my @F;
my ($start, $end) = (0,0);

#! Gen some test data
while ($start + $SIZE < $MAX) {
    $start += int rand($SIZE);
    $end = int $start + rand($SIZE);
    push @F, $start .. $end;
    $start = $end;
}

#! display it
print "@F";
#! and a range from it encompassing  two (possibly absent values)
print "@{[ range(\@F, $LO, $HI) ]}";

__DATA__
C:\test>229675 -MAX=50 -SIZE=5 -LO=15 -HI=35
2 3 4 5 5 6 7 8 9 12 13 17 18 19 20 21 21 22 23 24 25 29 30 31 33 34 3
+6 37 40 41 42 43 44 45 46 47
13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 3
+6
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