[GHC] #7858: Fix definitions of abs/signum for Floats/Doubles

[GHC]

#7858: Fix definitions of abs/signum for Floats/Doubles
-------------------------------------+-------------------------------------
              Reporter:  lerkok      |            Owner:  bernalex
                  Type:  bug         |           Status:  patch
              Priority:  normal      |        Milestone:  7.10.1
             Component:              |          Version:  7.6.3
  libraries/base                     |         Keywords:  floating point
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:  #9238
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D145   |
-------------------------------------+-------------------------------------

Comment (by Austin Seipp <austin@…>):

 In [changeset:"d9a20573f473cc7389004470999b8a318aa6b3f2/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="d9a20573f473cc7389004470999b8a318aa6b3f2"
 Make Prelude.signum handle -0.0 correctly (#7858)

 Summary:
 Make the `Float` and `Double` implementations of `signum` handle -0.0
 correctly per IEEE-754.

 This, together with "Make Prelude.abs handle -0.0 correctly (#7858)",
 fixes Trac #7858.

 Depends on D145

 Signed-off-by: Alexander Berntsen <alexander at plaimi.net>

 Test Plan:
 signum of (-0.0) should be (-0.0) not 0.0.

 Test program:

   main =
     putStrLn $ p ++ " " ++ n
     where
       f = show . signum
       p = f (-0.0 :: Double)
     n = f (0.0 :: Double)

 Reviewers: ekmett, hvr, rwbarton, austin

 Reviewed By: austin

 Subscribers: phaskell, simonmar, relrod, ezyang, carter

 Differential Revision: https://phabricator.haskell.org/D148

 GHC Trac Issues: #7858
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7858#comment:14>
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