Floating point manipulation : ulp and coerce IEEE-754 Double# into Word64#
There are currently two ways to compute the ulp of double numbers with GHC :
- Calling a C function, which requires to allocate a pointer. This is way too expensive when using interval arithmetic (for instance), that compute two ULPs at each arithmetic operations.
- Programming it by hand in haskell with GHC primitive operations, which requires using unsafeCoerce# : this does not work in GHC 6.12.2.
unsafeCoerce# should work, and there should be a primitive ulp# function in GHC, operating on Doubles at least. By the way, here is my haskell code using C for computing it :
foreign import ccall unsafe "math.h frexp" c_frexp::CDouble->(Ptr CInt)->IO ()
foreign import ccall unsafe "math.h ldexp" c_ldexp::CDouble->CInt->IO CDouble
ulp::Double->Double
ulp x=unsafePerformIO $ do
expon<-alloca (\e->do
c_frexp (realToFrac x) e
peek e)
(c_ldexp 0.5 $ expon-52) >>= return.realToFrac
Trac metadata
Trac field | Value |
---|---|
Version | 6.12.2 |
Type | FeatureRequest |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
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Blocking | |
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