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Chapter 12. Programming Considerations for 64-Bit Environments
enddo
!$omp do
do i=1,m
do j = 1, n
d = 30000.0D0*dble(i)+dble(j)+dble(j)
if(d .ne. c(i,j)) then
print *,"err i=",i,"j=",j
print *,"c(i,j)=",c(i,j)
print *,"d=",d
stop
endif
enddo
enddo
!$omp end parallel
print *, "M =",M,", N =",N
print *, "c(M,N) = ", c(m,n)
end
When compiled with the PGF95 compiler using –mcmodel=medium:
% pgf95 –mp –o mat mat.f –i8 –mcmodel=medium
% setenv OMP_NUM_THREADS 2
% mat
M = 16000 , N = 16000
c(M,N) = 480032000.0000000
Large Array and Small Memory Model in Fortran
The following example uses large, dynamically-allocated arrays. The code is divided into a main and
subroutine so you could put the subroutine into a shared library. Dynamic allocation of large arrays saves
space in the size of executable and saves time initializing data. Further, the routines can be compiled with 32bit compilers, by just decreasing the parameter size.
Example 12.3. Large Array and Small Memory Model in Fortran
% cat mat_allo.f90
program mat_allo
integer i, j
integer size, m, n
parameter (size=16000)
parameter (m=size,n=size)
double precision, allocatable::a(:,:),b(:,:),c(:,:)
allocate(a(m,n), b(m,n), c(m,n))
do i = 100, m, 1
do j = 100, n, 1
a(i,j) = 10000.0D0 * dble(i) + dble(j)
b(i,j) = 20000.0D0 * dble(i) + dble(j)
enddo
enddo
call mat_add(a,b,c,m,n)
print *, "M =",m,",N =",n
print *, "c(M,N) = ", c(m,n)
end
subroutine mat_add(a,b,c,m,n)
integer m, n, i, j
double precision a(m,n),b(m,n),c(m,n)
!$omp do
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