[GHC] #1042: Floating point exception

[GHC]

#1042: Floating point exception
-------------------------------------+-------------------------------------
              Reporter:  dons        |            Owner:
                  Type:  merge       |           Status:  new
              Priority:  normal      |        Milestone:  6.6.1
             Component:  Compiler    |          Version:  6.6
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  x86
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:  Incorrect   |       Blocked By:
  result at runtime                  |  Related Tickets:  #8695
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------
Changes (by dfeuer):

 * owner:  igloo =>
 * status:  closed => new
 * resolution:  fixed =>


Comment:

 I'm sorry to reopen an 8 year old bug, but I tripped over this today while
 attempting (unsuccessfully, so far) to write a version of `divModInt` that
 plays nice with CSE:

 {{{#!hs
 divModInt :: Int -> Int -> (Int, Int)
 (I# x) `divModInt` (I# y) = case x `divModInt#` y of
                             (# q, r #) -> (I# q, I# r)

 divModInt# :: Int# -> Int# -> (# Int#, Int# #)
 x# `divModInt#` y# = case x' `quotRemInt#` y# of
                        (# q, r #) -> (# q +# qadj, r +# radj #)
   where
     (# x', qadj, radj #) = if
       | isTrue# (x# ># 0#) && isTrue# (y# <# 0#) -> (# x# -# 1#, -1#, y#
 +# 1# #)
       | isTrue# (x# <# 0#) && isTrue# (y# ># 0#) -> (# x# +# 1#, -1#, y#
 -# 1# #)
       | otherwise                                -> (# x#, 0#, 0# #)
 }}}

 When I test this with

 {{{#!hs
 main = print $ divModInt minBound (-1)
 }}}

 I get a floating point exception. `GHC.Base.divMod` does not trip over
 this, even though it seems to be doing exactly the same arithmetic. As far
 as I can tell, this is ''supposed'' to be handled by `quotRemInt#`

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1042#comment:11>
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