[GHC] #3070: floor(0/0) should not be defined

[GHC]

#3070: floor(0/0) should not be defined
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    Reporter:  carette           |        Owner:  squadette       
        Type:  bug               |       Status:  new             
    Priority:  normal            |    Milestone:  6.12.1          
   Component:  Prelude           |      Version:  6.10.1          
    Severity:  normal            |   Resolution:                  
    Keywords:                    |   Difficulty:  Unknown         
    Testcase:                    |           Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |  
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Changes (by squadette):

  * owner:  => squadette
 * cc: squadette at gmail.com (added)

Comment:

 Same thing happens with exponent, significand, scaleFloat, truncate,
 round, and ceiling.

 I believe this patch should fix the problem:

 http://mynd.rinet.ru/~alexm/floor-3070.patch

 1. Of course, we get some performance hit, with two ifs for every call to
 those functions, and the appearance of `undefined' (may it confuse the
 optimizer somehow?)

 However, most of them seem to be not very performance oriented (except
 maybe for scaleFloat).

 2.  However, I believe that getting

    significand (0/0) = -0.75

 is not right, however fast it is.

 3. withValidDouble could probably be made a monad of some sort?

 4.  properFraction should be reindented if this patch is applied.  I did
 not make it to minimize changes.

 5. maybe we need a special compiler flag which means "do not bother
 checking floats for validity, let the user handle details.


 Thank you,

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3070#comment:3>
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