[GHC] #9530: min / max do not always return a NaN when one of the arguments is NaN

[GHC]

#9530: min / max do not always return a NaN when one of the arguments is NaN
-------------------------------------+-------------------------------------
              Reporter:  jrp         |            Owner:
                  Type:  bug         |           Status:  closed
              Priority:  normal      |        Milestone:
             Component:  Prelude     |          Version:  7.8.3
            Resolution:  invalid     |         Keywords:
      Operating System:  MacOS X     |     Architecture:  Unknown/Multiple
       Type of failure:  Incorrect   |       Difficulty:  Easy (less than 1
  result at runtime                  |  hour)
             Test Case:              |       Blocked By:  9276
              Blocking:              |  Related Tickets:  9276
Differential Revisions:              |
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Comment (by jrp):

 I don't have a copy of the standard, but
 http://en.wikipedia.org/wiki/IEEE_754_revision says
 {{{
 min(x,NaN) = min(NaN,x) = x
 max(x,NaN) = max(NaN,x) = x
 }}}

 which is not satisfied here

 {{{
 Prelude> max 3 nan
 3.0
 Prelude> max nan 3
 NaN
 }}}

 http://msdn.microsoft.com/en-
 gb/library/windows/desktop/jj218760(v=vs.85).aspx agrees:

 {{{
 The IEEE-754R specification for floating point min and max operations
 states that if one of the inputs to min or max is a quiet QNaN value, the
 result
  of the operation is the other parameter.
 }}}


 It goes on to add a further wrinkle:

 {{{
 A revision of the IEEE-754R specification adopted a different behavior for
 min
 and max when one input is a "signaling" SNaN value versus a QNaN value:
 }}}

 So far as I can tell, Haskell does not know anything about signalling
 NaNs, so this is probably not applicable.

 I'll change the title of the ticket to make the issue clear.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9530#comment:6>
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