cygwin gcc: Different numerical results in thread vs in main()

[Angelo Graziosi]

Brian Dessent wrote:

> Angelo Graziosi wrote:
> 
>> ... and in Fortran?
> 
> As long as you're using a recent gcc you can just use -mpc64.
> 

How recent?

With GFortran 4.3.1 and

$ cat test_case.0.f90
program test_case
   implicit none
   integer :: k
   integer, parameter :: DP = kind(1.D0),&
        N = 29
   real(DP), parameter :: A(0:N) = &
        (/1.0000000000000D0,3.8860009363293D0,7.4167881843083D0,&
          9.8599837415463D0,10.431383465276D0,9.4077161304727D0,&
          7.5332956276775D0,5.4995844630326D0,3.7275104474917D0,&
          2.3766149078263D0,1.4394444941337D0,0.8344437543616D0,&
          0.4657058294147D0,0.2514185849207D0,0.1317920740387D0,&
          0.0672995854816D0,0.0335554996094D0,0.0163785206816D0,&
          0.0078368645385D0,0.0036846299276D0,0.0017020281304D0,&
          0.0007756352209D0,0.0003469750783D0,0.0001544224626D0,&
          0.0000666379875D0,0.0000295655909D0,0.0000118821415D0,&
          0.0000057747681D0,0.0000017502652D0,0.0000014682034D0/)
   real(DP), parameter :: BB(0:N-1) = &
        (/(((k+2)*A(k+2)-A(k+1)*(A(1)+(k+1))),k = 0,N-2),&
          (-A(N)*(A(1)+N))/)
   real(DP) :: b(0:N-1),bbb(0:N-1)
   do k = 0,N-2
      b(k) = (k+2)*A(k+2)-A(k+1)*(A(1)+(k+1))
   enddo
   b(N-1) = -A(N)*(A(1)+N)
   bbb(0:N-1) = (/(((k+2)*A(k+2)-A(k+1)*(A(1)+(k+1))),k = 0,N-2),&
        (-A(N)*(A(1)+N))/)
   do k = 0,N-1
      print *, k,b(k)-BB(k),b(k)-bbb(k),BB(k)-bbb(k)
   enddo
end program test_case

$ gfortran -mpc64 test_case.0.f90 -o test_case.0

$ ./test_case.0
            0 -1.77635683940025046E-015 -1.77635683940025046E-015 
0.0000000000000000
            1 -3.55271367880050093E-015 -3.55271367880050093E-015 
0.0000000000000000
            2 -3.55271367880050093E-015 -3.55271367880050093E-015 
0.0000000000000000
            3 -7.10542735760100186E-015 -7.10542735760100186E-015 
0.0000000000000000
            4   0.0000000000000000        0.0000000000000000 
0.0000000000000000
            5   0.0000000000000000        0.0000000000000000 
0.0000000000000000
            ...

Only 13 (over 28) 0. 0. 0.!


     Angelo

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