That would work in most cases. The original code would also work for floating point values, whereas this version would need to change to ... <= 0 to handle that correctly. Under `use integer` it could also give the wrong answer due to overflow. In the general case it would be no faster than the original code, and can be slower.

> whereas this version would need to change to ... <= 0

IMHO for a multiplying approach that's the best check, even for the <=> version.

Simply changing to ... < 0 would check for the open interval excluding the endpoints. And ... == 0 for endpoints only.

But half-open intervals like [$a,$b[ can't be covered with this approach.

So I'd rather stick with

• $a <= $x and $x < $b
or the newer chained version
• $a <= $x < $b
and make sure the endpoints are previously swapped if necessary
• ($a,$b) = ($b,$a) if $b < $a;

update

and swapping can be made non-destructive by localizing it to a scope.

C:\tmp\e>perl
($a,$b) = (7,3);
my $x=5;
my $inside = do {
    local ($a,$b) = ($b,$a) if $b < $a;
    $a <= $x < $b ;
};
print "$x in [$a, $b]? $inside";
__END__
5 in [7, 3]? 1
C:\tmp\e>
[download]

(replace local with my for private vars)

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery}