[GHC] #9534: IEEE Standard 754 for Binary Floating-Point Arithmetic by Prof. W. Kahan, UCB

[GHC]

#9534: IEEE Standard 754 for Binary Floating-Point Arithmetic by Prof. W. Kahan,
UCB
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              Reporter:  jrp         |            Owner:
                  Type:  task        |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Test Suite  |          Version:  7.8.3
            Resolution:              |         Keywords:  IEEE754
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Moderate (less
       Type of failure:  Incorrect   |  than a day)
  result at runtime                  |       Blocked By:
             Test Case:              |  Related Tickets:
              Blocking:              |
Differential Revisions:              |
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Comment (by jrp):

 There is clearly no answer that is right for all uses: either the QNaN
 poisons the result (which is what you might expect, as it does so in all
 other arithmetic operations) or it doesn't (as in the IEE754r version).
 What seems to me to be clearly wrong is for the answer to depend on the
 order in which the arguments are presented.

 The underlying problem is that we are assuming that floating point numbers
 are orderable but they aren't when NaNs are included, so a definition of
 min / max in terms of the order relation is invalid.

 I think that the only answer is to have two separate min / max
 specialisations for floating point numbers and let the user decide which
 they need for their application.  Whether one of these is the default or
 they are two newly named functions is a pragmatic decision that depends on
 how much existing code would be broken, although I cannot imagine that
 there would be much code that relied on the order of the arguments.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9534#comment:4>
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