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use Benchmark;
 
...
              "substr" => sub { ($char) = substr($string,4,1);},
              "silly"  => sub { my $string2 = $string; $char = chop $s
+tring2 while length $string2 >= 4;}, #note the local
              });

Benchmark: running match, silly, substr, unpack, each for at least 1 C
+PU seconds...
     match:  3 wallclock secs ( 1.00 usr +  0.02 sys =  1.02 CPU) @ 18
+0382.35/s (n=183990)
     silly:  4 wallclock secs ( 1.15 usr +  0.09 sys =  1.24 CPU) @ 17
+341.13/s (n=21503)
    substr:  2 wallclock secs ( 1.00 usr +  0.05 sys =  1.05 CPU) @ 94
+4029.52/s (n=991231)
    unpack:  2 wallclock secs ( 1.02 usr +  0.06 sys =  1.08 CPU) @ 36
+2192.59/s (n=391168)