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#!/usr/bin/perl

...
        switchsign => sub { my $a = X; switchsign($a) },
        unsign => sub { my $a = X; unsign($a) },
        });

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Benchmark: timing 100000 iterations of switchsign, unsign...
switchsign:  4 wallclock secs ( 1.37 usr +  0.00 sys =  1.37 CPU) 
             @ 72992.70/s (n=100000)
    unsign:  4 wallclock secs ( 1.51 usr +  0.00 sys =  1.51 CPU) 
             @ 66225.17/s (n=100000)