#5688: instance Read Integer/Rational/Double readsPrec out of memory and crash
due
to exponential notation
---------------------------------+------------------------------------------
Reporter: gracjan | Owner: igloo
Type: bug | Status: patch
Priority: highest | Milestone: 7.4.1
Component: libraries/base | Version: 6.12.3
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: Runtime crash
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
---------------------------------+------------------------------------------
Comment(by igloo):
I assume the patch we want is 0001-Added-new-Exp-constructor-to-
Text.Read.Lex.Lexeme-so.patch?
There were a few warnings, most notably in the "`a`" variables here:
{{{
valueFracExp a (Just fs) mExp -- 4.3[e2]
= let (a,e) = fracExp (fromMaybe 0 mExp) a fs in Exp a e
}}}
which I assume was intended to be:
{{{
valueFracExp a (Just fs) mExp -- 4.3[e2]
= let (a', e) = fracExp (fromMaybe 0 mExp) a fs
in Exp a' e
}}}
`num008` then finds a number of differences, for example:
{{{
import Numeric
main :: IO ()
main = mapM_ (putStrLn . f) ["4.2000000e2", "1.8217369e0",
"1.8217369e-300"]
f :: String -> String
f str = let d :: Double
d = read str
in str ++ replicate (15 - length str) ' ' ++ show d
}}}
Before the patch:
{{{
$ ghc --make q
[1 of 1] Compiling Main ( q.hs, q.o )
Linking q ...
$ ./q
4.2000000e2 420.0
1.8217369e0 1.8217369
1.8217369e-300 1.8217369e-300
}}}
After the patch:
{{{
$ ghc --make q
[1 of 1] Compiling Main ( q.hs, q.o )
Linking q ...
$ ./q
4.2000000e2 420.00000000000006
1.8217369e0 1.8217368999999999
1.8217369e-300 1.8217368999999997e-300
}}}
Are we happy with that?
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5688#comment:27>
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