#5688: instance Read Integer/Rational/Double readsPrec out of memory and crash
due
to exponential notation
-------------------------------+--------------------------------------------
Reporter: gracjan | Owner: igloo
Type: bug | Status: new
Priority: highest | Milestone: 7.4.2
Component: libraries/base | Version: 6.12.3
Resolution: | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: Runtime crash | Difficulty: Unknown
Testcase: | Blockedby:
Blocking: | Related:
-------------------------------+--------------------------------------------
Comment(by maeder):
something like:
{{{
convert :: RealFloat a => Rational -> Integer -> a
convert frac expo =
let d = fromRational (frac * 10 ^^ expo)
in if abs expo + abs (fromIntegral (length (show $ numerator frac)
- length (show $ denominator frac)))
< fromIntegral (uncurry max $ floatRange d) then d
else case (frac < 0, expo < 0) of
(True, True) -> -0
(True, False) -> -1/0
(False, True) -> 0
(False, False) -> 1/0
}}}
floatRange returns 1024 for Double (that's the maximal size of the binary
exponent).
The size of the rational does almost not matter.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5688#comment:50>
GHC <http://www.haskell.org/ghc/>
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