title: Exponentiation in Ruby 1.8.7 Returns Wrong Answers
body: <p>I met this problem when I tried to compute 3**557 in irb.
  Ruby and MacRuby both are installed in my Mac (OS X 10.8). And the version of ruby is 1.8.7, of MacRuby 0.12 (ruby 1.9.2).
  rib and macirb gave me two different answers on computation of 3**557. (macirb's is right.)</p>
  
  <pre><code>$ irb
  &gt;&gt; 3**557
  =&gt; 54755702179342762063551440788945541007926808765326951193810107165429610423703291760740244724326099993131913104272587572918520442872536889724676586931200965615875242243330408150984753872526006744122187638040962508934109837755428764447134683114539218909666971979603
  
  $ macirb
  irb(main):001:0&gt; 3**557
  =&gt; 57087217942658063217290581978966727348872586279944803346410228520919738045995056049600505293676159316424182057188730248707922985741467061108015301244570536546607487919981026877250949414156613856336341922395385463291076789878575326012378057561766997352898452974964563
  </code></pre>
  
  <p>And then I tried something bigger, e.g. 3**5337, and I got the same answer this time.</p>
  
  <p>So, is this a bug in Ruby 1.8.7, or I should use another way to compute exponentiation?</p>