Haskell minimum/maximum Double Constant

Question

Is there any way in Haskell to get the constant that is the largest and smallest possible positive rational number greater than zero that can be represented by doubles?

Answer 1

GHC.Float has the function [floatRange][2]:

floatRange :: a -> (Int, Int) Source

a constant function, returning the lowest and highest values the exponent may assume

which should be what you want.

Answer 2

The fraction part of a double is 52 bits, so it can represent integers up to 4503599627370495 without losing precision.

The smallest possible positive non-zero integer would of course be one.

Answer 3

maxNonInfiniteFloat :: RealFloat a => a -> a
maxNonInfiniteFloat a = encodeFloat m n where
    b = floatRadix a
    e = floatDigits a
    (_, e') = floatRange a
    m = b ^ e - 1
    n = e' - e

minPositiveFloat :: RealFloat a => a -> a
minPositiveFloat a = encodeFloat 1 $ fst (floatRange a) - floatDigits a