Rate  regex substr
regex  21775/s     --   -27%
substr 29748/s    37%     --

##</code><code>##

$str='a'x1E6; 
=>
         Rate  regex substr
regex  15.1/s     --   -16%
substr 18.0/s    19%     --
$str='a'x1E7;
=>
         Rate  regex substr
regex  1.41/s     --   -21%
substr 1.79/s    27%     --

##</code><code>##

       s/iter  regex substr
regex    1.80     --   -21%
substr   1.42    27%     --