find_first_valid_block Subroutine

   PURE SUBROUTINE find_first_valid_block(pos, maxpos, blk_p)
      !! Finds the first valid block, inclusive from the current position.
      !! If there is no valid block, pos is set to 0

      INTEGER, INTENT(INOUT)                             :: pos
         !! input: current position; output: next valid position or 0
      INTEGER, INTENT(IN)                                :: maxpos
         !! maximal allowed position
      INTEGER, DIMENSION(:), INTENT(IN)                  :: blk_p
         !! block pointers, used to check validity

!   ---------------------------------------------------------------------------
!IF (pos .LT. 1) pos = 1

      DO WHILE (pos .LE. maxpos)
         IF (blk_p(pos) .EQ. 0) THEN
            pos = pos + 1
         ELSE
            EXIT
         END IF
      END DO
      IF (pos .GT. maxpos) pos = 0
   END SUBROUTINE find_first_valid_block