!!$ 
!!$              Parallel Sparse BLAS  v2.0
!!$    (C) Copyright 2006 Salvatore Filippone    University of Rome Tor Vergata
!!$                       Alfredo Buttari        University of Rome Tor Vergata
!!$ 
!!$  Redistribution and use in source and binary forms, with or without
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!!$  
!
! File: psi_ldsc_pre_halo.f90
!
! Subroutine: psi_ldsc_pre_halo
!   Build initial versions of data exchange lists.
!   When the descriptor is for a large index space, we cannot build 
!   the data exchange lists "on-the-fly", but we also want to keep using the 
!   same format conversion routines we use in the small index space case, 
!   hence this adapter routine.
!   Since it also convers the AVL tree data structure into the hashed list 
!   of ordered lists, it may be called to do just that; perhaps we should 
!   cut away that functionality and put it somewhere else...
!   
! 
! Arguments: 
!    desc     - type(psb_desc_type).    The communication descriptor.        
!    ext_hv   - logical                   Should we work on the halo_index.
!    info     - integer.                  return code.
!
subroutine psi_ldsc_pre_halo(desc,ext_hv,info)
  use psb_descriptor_type
  use psb_serial_mod
  use psb_const_mod
  use psb_error_mod
  use psb_penv_mod
  use psb_realloc_mod
  use psi_mod, psb_protect_name => psi_ldsc_pre_halo
  implicit none
  type(psb_desc_type), intent(inout) :: desc
  logical, intent(in)  :: ext_hv
  integer, intent(out) :: info

  integer,allocatable :: helem(:),hproc(:)
  integer,allocatable :: tmphl(:)

  integer          ::  i,j,np,me,lhalo,nhalo,&
       & n_col, err_act,  key, ih, nh, idx, nk,icomm
  integer             :: ictxt,n_row
  character(len=20)   :: name,ch_err

  info = 0
  name = 'psi_ldsc_pre_halo'
  call psb_erractionsave(err_act)

  ictxt = psb_cd_get_context(desc)
  icomm = psb_cd_get_mpic(desc)
  n_row = psb_cd_get_local_rows(desc)
  n_col = psb_cd_get_local_cols(desc)

  ! check on blacs grid 
  call psb_info(ictxt, me, np)
  if (np == -1) then
    info = 2010
    call psb_errpush(info,name)
    goto 9999
  endif


  if (.not.(psb_is_bld_desc(desc).and.psb_is_large_desc(desc))) then 
    info = 1122
    call psb_errpush(info,name)
    goto 9999
  end if

  call psi_bld_hash(desc,info)
  if (info /= 0) then 
    ch_err='psi_bld_hash'
    call psb_errpush(info,name,a_err=ch_err)
    goto 9999
  end if
  if (.not.ext_hv) then
    call psi_bld_tmphalo(desc,info)
    if (info /= 0) then 
      ch_err='psi_bld_tmphalo'
      call psb_errpush(info,name,a_err=ch_err)
      goto 9999
    end if
  end if

  call psb_erractionrestore(err_act)
  return

9999 continue
  call psb_erractionrestore(err_act)

  if (err_act.eq.psb_act_ret_) then
    return
  else
    call psb_error(ictxt)
  end if
  return


end subroutine psi_ldsc_pre_halo