When trying to mix precision in a simple program - using both real and double - and use the ddot procedure from BLAS, I come up with the wrong conclusion for the part with double precision. Here is the code:
program test
!! adding this statement narrowed the issue down to ddot being considered real(4)
implicit none
integer, parameter :: dp = kind(1.0d0)
!! The following 2 lines were added for the calls to the BLAS routines.
!! This fixed the issue.
real(dp), external :: ddot
real, external :: sdot
real, dimension(3) :: a,b
real(dp), dimension(3) :: d,e
integer :: i
do i = 1,3
a(i) = 1.0*i
b(i) = 3.5*i
d(i) = 1.0d0*i
e(i) = 3.5d0*i
end do
write (*,200) "sdot real(4) = ", sdot(3,a,1,b,1) ! should work and return 49.0
write (*,200) "ddot real(4) = ", ddot(3,a,1,b,1) ! should not work
write (*,200) "sdot real(8) = ", sdot(3,d,1,e,1) ! should not work
write (*,200) "ddot real(8) = ", ddot(3,d,1,e,1) ! should work and return 49.0
200 format(a,f5.2)
end program test
I tried to compile both gfortran and ifort using MKL BLAS libraries as follows:
ifort -lmkl_intel_lp64 -lmkl_sequential -lmkl_core
gfortran -lmkl_intel_lp64 -lmkl_sequential -lmkl_core main.f90
Conclusion:
sdot real(4) = 49.00
ddot real(4) = 0.00
sdot real(8) = 4.10
ddot real(8) = 0.00
How can I get the ddot procedure to handle double precision values correctly?
Also, adding the -autodouble (ifort) or -fdefault-real-8 (gfortran) flag makes both ddot routines work, but sdot routines fail.
Edit:
none ddot sdot. , , ddot .