search.f90

! Copyright (C) 2003-2018 John Young, Matthew Worsley
!
! This file is part of mfit.
!
! Mfit is free software: you can redistribute it and/or modify it
! under the terms of the GNU General Public License as published by
! the Free Software Foundation, either version 3 of the License, or
! (at your option) any later version.
!
! This program is distributed in the hope that it will be useful, but
! WITHOUT ANY WARRANTY; without even the implied warranty of
! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
! General Public License for more details.
!
! You should have received a copy of the GNU General Public License
! along with this program.  If not, see http://www.gnu.org/licenses/ .

module Search

  implicit none

  public

contains

  !============================================================================

  function locate(xx, x)

    !return index i such that xx(i) < x < xx(i+1)
    !xx must be monotonic

    !function arguments
    real, dimension(:) :: xx
    real :: x
    integer :: locate

    !local variables
    integer n, lower, mid, upper

    n = size(xx)
    lower = 0
    upper = n + 1
    do while (upper - lower > 1)
       mid = (upper + lower)/2
       if ((xx(n) > xx(1)).eqv.(x > xx(mid))) then
          lower = mid
       else
          upper = mid
       end if
    end do
    locate = lower

  end function locate

  !============================================================================

end module Search