searchsorted and quicksort in f90

searchtest.f90

module searchtools

    implicit none

contains

function searchsorted(all_values, sorted) result(cdf_idx)

    implicit none

    double precision, dimension(:), intent(in) :: all_values
    double precision, dimension(:), intent(in) :: sorted

    integer, allocatable, dimension(:) :: cdf_idx

    double precision :: val

    integer :: i, j, n, m

    n = size(all_values)-1
    m = size(sorted)

    allocate(cdf_idx(n))

    cdf_idx(:) = 0

    do i = 1, n

        val = all_values(i)

        do j = 1, m


            if (val < sorted(j)) then

                cdf_idx(i) = j - 1
                exit

            endif
            
        enddo

        if (cdf_idx(i) .eq. 0) then
           cdf_idx(i) = m
        endif
    enddo

end function searchsorted


recursive subroutine quicksort(a, first, last)
  implicit none
  double precision ::  a(*), x, t
  integer first, last
  integer i, j

  x = a( (first+last) / 2 )
  i = first
  j = last
  do
     do while (a(i) < x)
        i=i+1
     end do
     do while (x < a(j))
        j=j-1
     end do
     if (i >= j) exit
     t = a(i);  a(i) = a(j);  a(j) = t
     i=i+1
     j=j-1
  end do
  if (first < i-1) call quicksort(a, first, i-1)
  if (j+1 < last)  call quicksort(a, j+1, last)
end subroutine quicksort

end module searchtools

program main

    use searchtools!, only: searchsorted, qsort, group

    implicit none

    double precision, dimension(6) :: all_values
    double precision, dimension(3) :: u_sorted

    integer, allocatable, dimension(:) :: cdf_idx

    integer :: n

    all_values = (/0.2d0, 0.1d0, 0.3d0, 0.5d0, 0.6d0, 0.1d0/)

    n = size(all_values)

    write(*,*) all_values
    call quicksort(all_values,1,6)
    write(*,*) all_values


    ! all_values = (/0.1d0, 0.1d0, 0.2d0, 0.3d0, 0.5d0, 0.6d0/)
    u_sorted = (/0.1d0, 0.2d0, 0.3d0/)

    cdf_idx = searchsorted(all_values, u_sorted)
    write(*,*) cdf_idx

end program main