#5688: instance Read Integer/Rational/Double readsPrec out of memory and crash
due
to exponential notation
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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:
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Comment(by maeder):
Replying to [comment:49 igloo]:
> `fracExp` in `libraries/base/Text/Read/Lex.hs` makes the `Rational`, and
`fromRational` in `libraries/base/GHC/Float.lhs` converts the `Rational`
to a `Double/Float`.
Computing the possibly big Rational when reading is wrong in my eyes. The
Lexeme must store the fraction and (optional) exponent separately! Only
when converting to a floating point type you know how many digits in the
exponent may make sense. (`Float.lhs` is incomprehensible for me, but it
may do the right thing.)
(An alternative is to set a fixed limit of 6 digits in the exponent,
because more cannot be handled.)
Going via Rational is bad for bigger floating point numbers. The right
thing would be to compute the arguments for `encodeFloat` during
conversion.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5688#comment:52>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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