!   
!                Parallel Sparse BLAS  version 3.5
!      (C) Copyright 2006-2018
!        Salvatore Filippone    
!        Alfredo Buttari      
!   
!    Redistribution and use in source and binary forms, with or without
!    modification, are permitted provided that the following conditions
!    are met:
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!         notice, this list of conditions and the following disclaimer.
!      2. Redistributions in binary form must reproduce the above copyright
!         notice, this list of conditions, and the following disclaimer in the
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!      3. The name of the PSBLAS group or the names of its contributors may
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!         software without specific written permission.
!   
!    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
!    ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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!   
!    
!
! File: psi_crea_ovr_elem.f90
!
! Subroutine: psi_crea_ovr_elem
!   Creates the overlap_elem list: for each overlap index, store the index and 
!   the number of processes sharing it (minimum: 2). List is ended by -1.
!   See also description in base/modules/psb_desc_type.f90
! 
! Arguments: 
!    ovr_elem(:,:) - integer(psb_ipk_), allocatable  Array containing the output list    
!    desc_a   - type(psb_desc_type).       The communication descriptor.        
!    info     - integer.                   return code.
! 
subroutine psi_crea_ovr_elem(me,desc_overlap,ovr_elem,info)

  use psi_mod, psb_protect_name => psi_crea_ovr_elem
  use psb_realloc_mod
  use psb_error_mod
  use psb_penv_mod
  use psb_serial_mod
  implicit none

  !     ...parameter arrays....      
  integer(psb_ipk_), intent(in)               :: me, desc_overlap(:)
  integer(psb_ipk_), allocatable, intent(out) :: ovr_elem(:,:)
  integer(psb_ipk_), intent(out)              :: info

  !     ...local scalars...
  integer(psb_ipk_) :: i,pnt_new_elem,ret,j
  integer(psb_ipk_) :: dim_ovr_elem
  integer(psb_ipk_) :: pairtree(2)

  integer(psb_ipk_) :: nel, ip, ix, iel, insize, err_act, iproc
  integer(psb_ipk_), allocatable :: telem(:,:)

  character(len=20)    :: name


  info = psb_success_
  name='psi_crea_ovr_elem'


  if (allocated(ovr_elem)) then 
    dim_ovr_elem = size(ovr_elem,1)
  else
    dim_ovr_elem = 0
  endif


  insize = size(desc_overlap)
  insize = max(1,(insize+1)/2)
  allocate(telem(insize,3),stat=info)
  if (info /= psb_success_) then 
    info = psb_err_alloc_dealloc_
    call psb_errpush(info,name)
    goto 9999
  endif
  i   = 1
  nel = 0
  do while (desc_overlap(i) /= -1)
    !        ...loop over all procs of desc_overlap list....
    iproc = desc_overlap(i)
    i     = i+1
    do j=1,desc_overlap(i)
      nel = nel + 1 
      telem(nel,1) = desc_overlap(i+j)
      telem(nel,2) = 1
      telem(nel,3) = iproc
    enddo
    i=i+2*desc_overlap(i)+2
  enddo

  if (nel > 0) then 
    call psb_msort(telem(1:nel,1),ix=telem(1:nel,3),flag=psb_sort_keep_idx_)

    iel        = telem(1,1)
    telem(1,2) = 2
    telem(1,3) = min(me,telem(1,3))
    ix = 1
    ip = 2
    do 
      if (ip > nel) exit
      if (telem(ip,1) == iel) then 
        telem(ix,2) = telem(ix,2) + 1
        telem(ix,3) = min(telem(ix,3),telem(ip,3))
      else
        ix = ix + 1
        telem(ix,1) = telem(ip,1)
        iel         = telem(ip,1)
        telem(ix,2) = 2
        telem(ix,3) = min(me,telem(ip,3))
      end if
      ip = ip + 1
    end do
  else
    ix = 0
  end if

  nel = ix

  call psb_realloc(nel,3,telem,info)
  call psb_move_alloc(telem,ovr_elem,info) 

  call psb_erractionrestore(err_act)
  return

9999 call psb_error_handler(err_act)

  return

end subroutine psi_crea_ovr_elem