sum on array longer than max value

[Patrice_l_]

Hi all,

I just discover than the sum intrinsic function use the type of the array ( I guess) to do the sum and therefor if the array is longer than the max value of type. I don't know if that is defined in the standard, is there a solution to this other than custom sum function ?

program sum1
integer(1),dimension(200) :: int1
integer(2),dimension(200000) :: int2

int1=1
int2=1
print *,sum(int1)
print *,sum(int2)
end program

Gives the results  -56   3392.

Thanks for your thoughts on this.

P.

[Steven_L_Intel1]

The standard doesn't allow for the result being a different "kind" from that of the argument, if that's what you're asking for. Your program creates a value that exceeds the range of the integer kind, therefore the program's behavior is not specified by the standard.

[Patrice_l_]

Thanks Steve that was the question.

[TimP]

sum(int(int2,int32)) is valid syntax under 'use iso_fortran_env' in case that is what you want.  If you omit ,int32 it should promote to default int kind.
 

[Patrice_l_]

I think that this way generates a copy of the array first ?

I don't see that being a solution since this is done a lot of time on shiftting array.

[TimP]

I suppose you could submit a feature request if you find this expression isn't optimized, as well as trying a DO loop.

[jimdempseyatthecove]

What you might consider doing is creating one or two generic functions. One returning an integer(4) and the other returning integer(8) (assuming you want the integer(8)). then make 4 dispatch routines based on the size of an element in the array.

function sum_4_2(x) result(ret)
  integer(2) :: x(:) ! get dimension from array descriptor on call
  integer(4) :: ret
  integer :: i
  ret = 0 ! not necessary, reduction implies zeroing, here for clarity of operation
  !DIR$ SIMD REDUCTION(+:ret)
  do i=lbound(x), ubound(x)
    ret = ret + int(x(i),kind(ret)) ! should optimize to _mm_cvtepi16_epi32
  end do
end function sum_4_2

You can add the interface and other routines.

Jim Dempsey