@hackage qd0.4

This package supports both a double-double datatype (approx. 32 decimal digits) and a quad-double datatype (approx. 64 decimal digits), using libqd (which is implemented in C++ with C and Fortran wrappers). To compile this package you need libqd to be installed.

Numeric.QD.DoubleDouble.DoubleDouble and Numeric.QD.QuadDouble.QuadDouble are strict tuples of CDoubles, with instances of: Eq, Floating, Fractional, Num, Ord, Read, Real, RealFloat, RealFrac, Show, Storable, Typeable.

Additional note: libqd depends on 64bit doubles, while some FPU architectures use 80bit. It is highly recommended to compile with -fno-excess-precision and set the FPU control words to avoid erroneous behaviour, perhaps by doing something like this at the start of your program:

import Foreign (nullPtr)
import GHC.Conc (forkOnIO, numCapabilities)
import Numeric.QD.FPU.Raw (fpu_fix_start)
main :: IO ()
main = do
  mapM_ (flip forkOnIO $ fpu_fix_start nullPtr) [ 0 .. numCapabilities - 1 ]
  -- ...