Re: Supporting IEEE 754 [exceptions] (in a front end [gfortran])

[Tobias Burnus <burnus at net-b dot de>]

Joseph S. Myers wrote:
>> My biggest issue is that I don't see how I can compile-time evaluate the
>> following - or how to evaluate it at all:
>>
>> if (IEEE_SUPPORT_NAN(x)) &    ! should be always true (or false) on a
>> given system
>>     
> See MODE_HAS_NANS etc. in real.h
>   
Thanks. There I find:
- MODE_HAS_NANS
- MODE_HAS_INFINITIES
- MODE_HAS_SIGNED_ZEROS
- MODE_HAS_SIGN_DEPENDENT_ROUNDING

Those match IEEE_SUPPORT_INF, IEEE_SUPPORT_NAN. However, Fortran 2003
has additionally:
- IEEE_SUPPORT_ROUNDING (which can be catered for using the presence of
fenv.h's FE_DOWNWARD etc.)

and also the following items:
a) IEEE_SUPPORT_DIVIDE - Inquire whether the processor supports divide
with the accuracy specified by the IEEE International Standard.
b) IEEE_SUPPORT_DENORMAL - Inquire whether the processor supports IEEE
denormalized numbers.
c) IEEE_SUPPORT_SQRT - Inquire whether the processor implements SQRT in
accord with the IEEE Inter19
national Standard. (In this case, SQRT(-0.0) has the value -0.0.)
d) IEEE_SUPPORT_UNDERFLOW_CONTROL - Inquire whether the procedure
supports the ability to control the underflow mode during program execution.

For the latter four I don't see where I can obtain those pieces of
information. Additionally, one is supposed to set (if possible) whether
(1) denormal numbers are used or (2) denormals are zero (DAZ); I have
not seen an easy option to set/query. (SSE2 seems to allows DAZ,
cf.gcc/config/i386/crtfastmath.c)

Tobias