xdf_closest_type() selects among the data types supported by the file referenced by xdf the type that is
the closest to the target argument. The selected type can then be safely used in a call to
xdf_set_chconf(3) with the XDF_CF_STOTYPE field.
The selection algorithm is based on the 3 following criterions (cited by priority, i.e. most important
cited first): data size, signed/unsigned type, float/integer value. The data size criterion forces the
selected type to have a data size (number of byte to represent the value) equal or bigger than the one of
the target type (with a preference with sizes the closest to the size of target). The signed/unsigned
criterion tries to select a type that has the same signeness (signed or unsigned data type) as the
target. Finally the float/integer criterion tries to select a floating point type if target is float or
double or an integer data type if target is an integer type.
As a consequence, if target is supported by the underlying file format of xdf, the function is ensured to
return target.