On the SPU, all single-precision floating-point arithmetic always
takes place in round-to-zero rounding mode. The Fortran front-end
always assumes round-to-nearest mode. This causes a number of issues:
- Both real->string and string->real transformations (e.g. printf, scanf)
operate in round-to-zero mode. This means that a round-trip transform
will often not yield an identical result; this causes e.g. the
default_format_1.f90 test case to fail.
It seems this cannot be fixed as the behaviour of printf and scanf
is specified to follow round-to-zero on the SPU ...
- As a special case of the real->string->real round-trip transform problem,
the value of GFC_REAL_4_HUGE from the (generated) kinds.h does not convert
to the largest real when read back in, but its immediate predecessor.
This causes the scalar_mask_2.f90 test case to fail.
This can be fixed by using rounding away from zero when generating the
string constant that is written to the kinds.h file.
- Compile-time operations performed by the Fortran front-end are always
done in round-to-nearest mode. This results in different results as
compared to executing the corresponding operations at run-time. This
causes e.g. the integer_exponentiation_3.F90 test case to fail.
This can be fixed by having the Fortran front-end check the target
floating format rounding mode, and using this mode to perform
compile-time operations in.
--
Summary: Support round-to-zero in Fortran front-end
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: uweigand at gcc dot gnu dot org
GCC target triplet: spu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39795
