Fortran compiler strangeness

[Stefano Simonucci]

Hi. 
I have used gfortran to compile a little program 
with the command 
gfortran -O2 prova.f    

      program prova
      parameter(Nx=10000,Ny=10000)
      real*8 A(Nx,Ny),X(Nx),Y(Ny)
      do i=1,Nx
       X(i)=2./(Nx+1)*i-1
      end do
      do i=1,Ny
       Y(i)=2./(Ny+1)*i-1
      end do
      do i=1,Nx
      do j=1,Ny
      A(i,j)=sin(1.+i+j);
      end do
      end do
      end program

then I have execute the program
 
time ./a.out 

real    1m58.509s
user    1m57.035s
sys     0m0.792s

An analogous program in C takes 22 sec.
Then I have changed sin(1.+i+j) with sin(1.d0+i+j) 
and I get the following execution time


real    0m23.868s
user    0m22.737s
sys     0m0.864s

This behaviour seems strange.
Thank you

   
-- 
Stefano Simonucci <stefano.simonucci@unicam.it>