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

[GHC]

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

Comment (by Scott Turner):

 The patch fails for negative x.
 {{{
 Prelude Data.Complex> (-1)**(0.5) :: Complex Double
 NaN :+ 0.0
 }}}
 The result needs to be near either 0:+1 or 0:+(-1).

 The existing exp (log x * y) is basically good as long as x is not 0 or
 infinity.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8539#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler