Hi all,
I'm working on implementing a correct Fortran rounding (rounding to
nearest-integer, with half integer values rounded to the integer of
maximum absolute value) in the Fortran front-end, following
ada/trans.c (convert_with_check) and
http://gcc.gnu.org/ml/fortran/2005-04/msg00139.html
The code Ada uses to do it has the following comments:
/* The following calculations depend on proper rounding to even
of each arithmetic operation. In order to prevent excess
precision from spoiling this property, use the widest hardware
floating-point type.
FIXME: For maximum efficiency, this should only be done for machines
and types where intermediates may have extra precision. */
calc_type = longest_float_type_node;
/* FIXME: Should not have padding in the first place */
if (TREE_CODE (calc_type) == RECORD_TYPE
&& TYPE_IS_PADDING_P (calc_type))
calc_type = TREE_TYPE (TYPE_FIELDS (calc_type));
I have the three following questions, probably best directed to
middle-end experts and Ada maintainers:
* How can I know the longest float type? My first patch uses the
long_double_type_node unconditionally, but it surely isn't a generic
solution
* How can I determine if a given type may have extra precision?
* What is this padding code doing, and is it necessary?
Thanks,
FX
