[GHC] #15271: 1e1000000000 :: Double yields 0.0 instead of Infinity

[GHC]

#15271: 1e1000000000 :: Double yields 0.0 instead of Infinity
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        Reporter:  claude            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by fangyizhou):

 {{{
 main = do
   print 1e646457008 -- This is infinity
   print 1e646457009 -- This incorrectly printed 0.0
   print 1e1555550000 -- This is still infinity
   print 1e1000000000 -- This incorrectly printed 0.0
 }}}

 This is some wraparound behaviour, which is why I thought there is an
 integer overflow.

  I used `trace` to print the value of `(I# (ln# -# ld# +# 1# -# md#))`
 (https://github.com/ghc/ghc/blob/21f0f56164f50844c2150c62f950983b2376f8b6/libraries/base/GHC/Float.hs#L1072)


 1e646457008 -> 2147483645 (infinity)

 1e646457009 -> 2147483648 (0.0, overflow to negative)

 1e1000000000 -> 3321928042 (infinity, overflow to positive)

 1e1555550000 -> 5167425196 (0.0, overflow to negative)

 Any suggestions on how to fix?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15271#comment:5>
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