!!$ 
!!$              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
!!$  modification, are permitted provided that the following conditions
!!$  are met:
!!$    1. Redistributions of source code must retain the above copyright
!!$       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
!!$       documentation and/or other materials provided with the distribution.
!!$    3. The name of the PSBLAS group or the names of its contributors may
!!$       not be used to endorse or promote products derived from this
!!$       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
!!$  TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
!!$  PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE PSBLAS GROUP OR ITS CONTRIBUTORS
!!$  BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
!!$  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
!!$  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
!!$  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
!!$  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
!!$  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
!!$  POSSIBILITY OF SUCH DAMAGE.
!!$ 
!!$  
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, only : psi_fnd_owner
  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,err,np,me,lhalo,nhalo,&
       & n_col, err_act,  key, ih, nh, idx, nk,icomm,hsize
  integer             :: ictxt,n_row
  logical, parameter  :: debug=.false., debugwrt=.false.
  character(len=20)   :: name,ch_err

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

  ictxt   = psb_cd_get_context(desc)
  n_row   = psb_cd_get_local_rows(desc)
  n_col   = psb_cd_get_local_cols(desc)
  call psb_get_mpicomm(ictxt,icomm )

  ! 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


  nk = n_col
  call psb_realloc(nk,2,desc%glb_lc,info) 
  if (info ==0) call psb_realloc(psb_hash_size+1,desc%hashv,info,lb=0)
  if (info /= 0) then 
    ch_err='psb_realloc'
    call psb_errpush(info,name,a_err=ch_err)
    goto 9999
  end if

  desc%hashv(0:psb_hash_size) = 0
  do i=1, nk
    key = desc%loc_to_glob(i)
    ih  = iand(key,psb_hash_mask) 
    desc%hashv(ih) = desc%hashv(ih) + 1
  end do
  nh = desc%hashv(0) 
  idx = 1
  do i=1, psb_hash_size
    desc%hashv(i-1) = idx
    idx = idx + nh
    nh = desc%hashv(i)
  end do
  do i=1, nk
    key = desc%loc_to_glob(i)
    ih  = iand(key,psb_hash_mask)
    idx = desc%hashv(ih) 
    desc%glb_lc(idx,1) = key
    desc%glb_lc(idx,2) = i
    desc%hashv(ih) = desc%hashv(ih) + 1
  end do
  do i = psb_hash_size, 1, -1 
    desc%hashv(i) = desc%hashv(i-1)
  end do
  desc%hashv(0) = 1
  do i=0, psb_hash_size-1 
    idx = desc%hashv(i)
    nh  = desc%hashv(i+1) - desc%hashv(i) 
    if (nh > 1) then 
      call psb_msort(desc%glb_lc(idx:idx+nh-1,1),&
           & ix=desc%glb_lc(idx:idx+nh-1,2),flag=psb_sort_keep_idx_)
    end if
  end do

  if (.not.ext_hv) then
    nh = (n_col-n_row)
    if (nh > 0) then 
      Allocate(helem(nh),stat=info)
      if (info /= 0) then 
        call psb_errpush(4010,name,a_err='Allocate')
        goto 9999      
      end if

      do i=1, nh
        helem(i) = desc%loc_to_glob(n_row+i)
      end do

      call psi_fnd_owner(nh,helem,hproc,desc,info)
      allocate(tmphl((3*((n_col-n_row)+1)+1)),stat=info)
      if (info /= 0) then 
        call psb_errpush(4010,name,a_err='Allocate')
        goto 9999      
      end if
      j  = 1
      do i=1,nh
        tmphl(j+0) = hproc(i)
        if (tmphl(j+0)<0) then 
          write(0,*) 'Unrecoverable error: missing proc from asb'
        end if
        tmphl(j+1) = 1
        tmphl(j+2) = n_row+i
        j          = j + 3
      end do
      tmphl(j) = -1
      lhalo = j
      nhalo = (lhalo-1)/3
    else 
      allocate(tmphl(1),stat=info) 
      if (info /= 0) then 
        call psb_errpush(4010,name,a_err='Allocate')
        goto 9999      
      end if
      tmphl=-1
    endif
    call psb_transfer(tmphl,desc%halo_index,info)
  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