#3898: Many floating point documentation/behaviour mismatches.
---------------------------------+------------------------------------------
Reporter: draconx | Owner:
Type: bug | Status: new
Priority: normal | Component: libraries/base
Version: 6.12.1 | Keywords:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: None/Unknown
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I was looking at the haddock documentation for the Prelude to find out
what the heck isIEEE did (which didn't actually help: what makes a value
an "IEEE floating point number"? I'm guessing it is a constant function
which indicates conformance of the _type_ to a particular standard), when
I found a number of mismatches between the documentation and the
behaviour.
* The documentation for scaleFloat says "multiplies a floating point
number by an integer power of the radix". But it doesn't do this:
{{{
floatRadix (1/0)
--> 2
1/0 * 2^^(-1)
--> Infinity
scaleFloat (-1) (1/0)
--> 8.98846567431158e307
}}}
In this case, I consider the documentation correct and the implementation
wrong: scaleFloat should behave similarly to C's scalbln.
* The documentation for exponent says "the second component of
decodeFloat".
{{{
decodeFloat 5
--> (5629499534213120,-50)
exponent 5
--> 3
}}}
In this case, it is probably just the documentation that is wrong.
* The documentation for encodeFloat says "performs the inverse of
decodeFloat".
{{{
id $ 0/0
--> NaN
uncurry encodeFloat . decodeFloat $ 0/0
--> -Infinity
}}}
In this case, I'm not sure which is wrong.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3898>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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