[GHC] #8539: Data.Complex shouldn't use default implementation of (**)

[GHC]

#8539: Data.Complex shouldn't use default implementation of (**)
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              Reporter:              |            Owner:
  jjaredsimpson                      |           Status:  patch
                  Type:  bug         |        Milestone:  7.10.1
              Priority:  low         |          Version:  7.6.3
             Component:  Prelude     |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Easy (less than 1
  Unknown/Multiple                   |  hour)
       Type of failure:  Incorrect   |       Blocked By:
  result at runtime                  |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by dfeuer):

 One minor concern: will the optimizer do the right thing checking `exp_re
 < 0` and `exp_re > 0`, or will we be better off with `case compare 0
 exp_re ...`?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8539#comment:31>
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