Work Mapping

Loop directive

The loop construct specifies that each iteration of the following loop is executed by a node set specified by the on clause, so that the iterations are distributed among nodes and executed in parallel.

• Specify the index to be divided between the loop and on statements. In the case of a single loop statement, this can be omitted.
• on-ref specifies the template name or the node set name.
• An operation of reduction clause is defined as follows.

[F] +, *, -, .and., .or., .eqv., .neqv., max, min, iand, ior, ieor, firstmax, firstmin, lastmax, lastmin
[C] +, *, -, &, |, ^, &&, ||, max, min, firstmax, firstmin, lastmax, lastmin

Single loop

#pragma xmp loop on t[i]
for( i = 0; i < 20; i++){
   a[i] = func(i);
}

!$xmp loop on t(i)
do i=1, 20
   a(i) = func(i)
end do

Nested loop

#pragma xmp loop (i,j) on t[i][j]
for( i = 0; i < 20; i++){
   for( j = 0; j < 10; j++){
      a[i][j] = func(i , j);
   }
}

!$xmp loop (i,j) on t(i,j)
do j=1, 10
   do i=1, 20
      a(i, j) = func(i, j)
   end do
end do

Reduction clause

#pragma xmp loop on t[i] reduction(+:sum)
for( i = 0; i < 20; i++){
   sum += i;
}

!$xmp loop on t(i) reduction(+:sum)
do i=1, 20
   sum = sum + i
end do

The following calculation is performed at each node (with four nodes).

After the end of the loop statement, the reduction clause causes a summation calculation to be performed based on the value of sums held at each node. In this case, a value of 190 in C, and a value of 210 in Fotran, is assigned to the sum in each node.