Generic binarySearch algorithm in Fortran 2003 (pure, recursive)

binsearchtest.f90

program binSearchTest

  integer :: idx
  real, allocatable :: v(:)
  integer, allocatable :: v2(:)

  interface binarySearch
     procedure binarySearch_real
     procedure binarySearch_int
  end interface binarySearch

  ! Test code
  allocate(v(100))
  allocate(v2(100))
  
  do idx = 1, size(v)
     v(idx) = idx * 1.2
  end do
  
  do idx = 1,size(v2)
     v2(idx) = idx*2
  end do

  idx = binarySearch(v, 42.1)
  print *, idx, v(idx), v(idx+1)

  idx = binarySearch(v2, 120)
  print *, idx, v2(idx), v2(idx+1)
  
!
contains
  pure recursive function binarySearch_real(vec, scal, min, max) result (idx)
    ! input parameters
    real, intent(in)              :: vec(:)
    real, intent(in)              :: scal
    integer, optional, intent(in) :: min
    integer, optional, intent(in) :: max

    ! result
    integer           :: idx

    !locals
    integer           :: i
    
    ! logic    
    if(.not.present(min)) then
       idx = binarySearch_real(vec,scal, 1, size(vec))
    else

       i = ishft(min+max, -1)
       
       if(scal >= vec(i) .and. scal < vec(i+1)) then
          idx = i
          
       else if( scal < vec(i) ) then
          idx = binarySearch_real(vec,scal, min, ishft(min+max, -1) - 1)
          
       elseif(scal > vec(i)) then
          idx = binarySearch_real(vec,scal, ishft(min+max, -1) + 1, max)
       end if
    end if
  end function binarySearch_real

 pure recursive function binarySearch_int(vec, scal, min, max) result (idx)
    ! input parameters
    integer, intent(in)              :: vec(:)
    integer, intent(in)              :: scal
    integer, optional, intent(in)    :: min
    integer, optional, intent(in)    :: max

    ! result
    integer           :: idx

    !locals
    integer           :: i
    
    ! logic    
    if(.not.present(min)) then
       idx = binarySearch_int(vec,scal, 1, size(vec))
    else

       i = ishft(min+max, -1)
       
       if(scal >= vec(i) .and. scal < vec(i+1)) then
          idx = i
          
       else if( scal < vec(i) ) then
          idx = binarySearch_int(vec,scal, min, ishft(min+max, -1) - 1)
          
       elseif(scal > vec(i)) then
          idx = binarySearch_int(vec,scal, ishft(min+max, -1) + 1, max)
       end if
    end if
  end function binarySearch_int

end program binSearchTest