[GHC] #8780: abs for IEEE floating point is slightly wrong.

13 Feb 2014


      #8780: abs for IEEE floating point is slightly wrong.
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       Reporter:  augustss          |             Owner:
           Type:  bug               |            Status:  new
       Priority:  low               |         Milestone:
      Component:  Compiler          |           Version:  7.6.3
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 Evaluating abs(-0) gives the answer -0.  This unexpected since it breaks
 invariants like 1/(abs x) >= 0.  So abs(-0) should be 0.  This is also the
 norm for other languages.

 Together with this change, signum should also be changed so signum(-0) is
 -0.  This maintains the invariant abs x * signum x == x.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8780
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