floatRange gives unexpected results

Here's the signature for floatRange in base/GHC/Float.hs:

-- | a constant function, returning the lowest and highest values
-- the exponent may assume
floatRange          :: a -> (Int,Int)

And here are the results for Float and Double:

>>> floatRange (undefined :: Float)
(-125,128)

>>> floatRange (undefined :: Double)
(-1021, 1024)

This is quite surprising to me given the documentation for the function. Single-precision floating-point numbers have a maximum exponent of 127 and a minimum exponent of -126 (-149 for subnormalized floats). Double-precision floating-point numbers have a maximum exponent of 1023 and a minimum exponent of -1022 (-1074 for subnormalized doubles). This means either the documentation is faulty or the implementation is.

Tracking this down the issue seems to be the definition of the constants in base/includes/ieee-flpt.h:

   /* Minimum int x such that FLT_RADIX**(x-1) is a normalised float */
#if !defined(FLT_MIN_EXP)  
#  define FLT_MIN_EXP (-125)
#endif

And similar for the other constants, truncated:

# define FLT_MAX_EXP 128
#  define DBL_MIN_EXP (-1021)
# define DBL_MAX_EXP 1024

As the comment for FLT_MIN_EXP states, these numbers are all shifted by 1 in the direction of positive infinity. I have no idea why this is. The definitions for floatRange for Float, respectively Double are as follows:

floatRange _        =  (FLT_MIN_EXP, FLT_MAX_EXP) -- ditto [ditto refers to "from float.h", which doesn't exist and should probably be "ieee-flpt.h"]
floatRange _        =  (DBL_MIN_EXP, DBL_MAX_EXP) -- ditto

So if floatRange is supposed to do what I think it should and what its documentation says it does either these constants or the implementations of floatRange for Float and Double need to change.