#!/usr/bin/perl

use Benchmark;

sub switchsign
{
  if (substr($_[0],0,1) eq '-')
  {
    substr($_[0],0,1)='+';
  }
  elsif (substr($_[0],0,1) eq '+')
  {
    substr($_[0],0,1)='-';
  }
  else
  {
    substr($_[0],0,0)='-';
  }
}

sub unsign
{
  if (substr($_[0],0,1) eq '-')
  {
    substr($_[0],0,1)='';
  }
  elsif (substr($_[0],0,1) eq '+')
  {
    substr($_[0],0,1)='-';
  }
  else
  {
    substr($_[0],0,0)='-';
  }
}

use constant X => '-'.'99999';

timethese(100_000, {
        switchsign => sub { my $a = X; switchsign($a) },
        unsign => sub { my $a = X; unsign($a) },
        });

##</code><code>##

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)