Tim Prince <timothyprince@xxxxxxxxxxxxx> comments on my posting about
128-bit floating-point arithmetic support on AMD64 and other
architectures:
>> Several of those Fortran compilers support 128-bit floating point in
>> software.
I just made experiments with all of the Fortran compilers that I have
on AMD64: only icc was even willing to compile code with REAL*16
declarations, and it did indeed use 128-bit arithmetic with a 113-bit
significand.
Here are the versions of Fortran compilers that I just tried:
g77 GNU Fortran (GCC) 3.3.5
[won't compile REAL*16]
gfortran GNU Fortran 95 (GCC 4.0.2 20051130 (Red Hat 4.0.2-14.EL4))
[won't compile REAL*16]
ifort Intel(R) Fortran Compiler for Intel(R) EM64T-based applications,
Version 8.1 Build 20060606 Package ID: l_fce_pc_8.1.037
pathf90 PathScale EKOPath(TM) Compiler Suite: Version 2.5
[won't compile REAL*16]
pgf90 5.2-1 and 6.2-3
[won't compile REAL*16]
sunf90 Sun Fortran 95 8.3 Linux_i386 Build27_2 2006/08/02
[won't compile REAL*16]
For the record, here is the simple Fortran 77 test program that I
used:
% cat qeps.f
REAL*16 store
REAL*16 eps
INTEGER k
eps = 1.0q0
k = 0
10 IF (store(1.0q0 + eps/2.0q0) .NE. 1.0q0) THEN
k = k - 1
eps = eps/2.0q0
GO TO 10
END IF
WRITE (6,'(2x, i6, 2x, 1pE45.35e4)') k, eps
WRITE (6,'(2x, i6, 2x, z32.32)') k, eps
END
REAL*16 FUNCTION store(x)
REAL*16 x
store = x
END
For Fortran 90/95 buffs, here is an alternate version:
% cat qeps.f90
real (kind = 16) :: store
real (kind = 16) :: eps
INTEGER k
eps = 1.0q0
k = 0
10 IF (store(1.0q0 + eps/2.0q0) .NE. 1.0q0) THEN
k = k - 1
eps = eps/2.0q0
GO TO 10
END IF
WRITE (6,'(2x, i6, 2x, 1pE45.35e4)') k, eps
WRITE (6,'(2x, i6, 2x, z32.32)') k, eps
END
FUNCTION store(x)
real (kind = 16) :: store
real (kind = 16) :: x
store = x
END
There was no difference in the handling of the two versions of the
test program by the listed compilers: only Intel ifort compiled the
code.
Sun Solaris SPARC f77, f90, and f95 all happily accept the programs.
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