diff --git a/base/internals/psi_desc_impl.f90 b/base/internals/psi_desc_impl.f90
index 8bf881176..81aa4a2e0 100644
--- a/base/internals/psi_desc_impl.f90
+++ b/base/internals/psi_desc_impl.f90
@@ -29,273 +29,302 @@
 !!$  POSSIBILITY OF SUCH DAMAGE.
 !!$ 
 !!$  
+submodule (psi_i_mod) psi_desc_impl_mod
+
+contains
+
+  subroutine psi_renum_index(iperm,idx,info)
+    use psb_serial_mod 
+    implicit none 
+
+    integer(psb_ipk_), intent(out)   :: info
+    integer(psb_ipk_), intent(in)    :: iperm(:)
+    integer(psb_ipk_), intent(inout) :: idx(:)
+
+    integer(psb_ipk_) :: i,j,k,nh
+
+    i=1
+    k=idx(i)
+    do while (k /= -1) 
+      i = i+1
+      nh = idx(i)
+      do j = i+1, i+nh
+        idx(j) = iperm(idx(j))
+      enddo
+      i  = i + nh + 1
+      nh = idx(i)
+      do j = i+1, i+nh
+        idx(j) = iperm(idx(j))
+      enddo
+      i = i + nh + 1
+      k = idx(i)
+    enddo
 
-subroutine psi_renum_index(iperm,idx,info)
-  use psi_mod, psi_protect_name =>  psi_renum_index
-  use psb_serial_mod 
-  implicit none 
+  end subroutine psi_renum_index
+
+  subroutine psi_cnv_dsc(halo_in,ovrlap_in,ext_in,cdesc, info, mold)
+    use psb_realloc_mod
+    implicit none
+
+    !     ....scalars parameters....
+    integer(psb_ipk_), intent(in)                :: halo_in(:), ovrlap_in(:),ext_in(:)
+    type(psb_desc_type), intent(inout) :: cdesc
+    integer(psb_ipk_), intent(out)               :: info
+    class(psb_i_base_vect_type), optional, intent(in) :: mold
+
+    !     ....local scalars....      
+    integer(psb_ipk_) :: np,me
+    integer(psb_ipk_) :: ictxt, err_act,nxch,nsnd,nrcv,j,k
+    !     ...local array...
+    integer(psb_ipk_), allocatable  :: idx_out(:), tmp_mst_idx(:)
+
+    !     ...parameters
+    integer(psb_ipk_) :: debug_level, debug_unit
+    logical, parameter :: debug=.false.
+    character(len=20)  :: name
+
+    name='psi_cnv_desc'
+    call psb_get_erraction(err_act)
+    debug_level = psb_get_debug_level()
+    debug_unit  = psb_get_debug_unit()
+
+    info = psb_success_
+    ictxt = cdesc%get_context()
+
+    call psb_info(ictxt,me,np)
+    if (np == -1) then
+      info = psb_err_context_error_
+      call psb_errpush(info,name)
+      goto 9999
+    endif
+
+
+    ! first the halo index
+    if (debug_level>0) write(debug_unit,*) me,'Calling crea_index on halo',&
+         & size(halo_in)
+    call psi_crea_index(cdesc,halo_in, idx_out,.false.,nxch,nsnd,nrcv,info)
+    if (info /= psb_success_) then
+      call psb_errpush(psb_err_from_subroutine_,name,a_err='psi_crea_index')
+      goto 9999
+    end if
+    call psb_move_alloc(idx_out,cdesc%halo_index,info)
 
-  integer(psb_ipk_), intent(out)   :: info
-  integer(psb_ipk_), intent(in)    :: iperm(:)
-  integer(psb_ipk_), intent(inout) :: idx(:)
+    if (debug_level>0) write(debug_unit,*) me,'Done crea_index on halo'
+    if (debug_level>0) write(debug_unit,*) me,'Calling crea_index on ext'
 
-  integer(psb_ipk_) :: i,j,k,nh
 
-  i=1
-  k=idx(i)
-  do while (k /= -1) 
-    i = i+1
-    nh = idx(i)
-    do j = i+1, i+nh
-      idx(j) = iperm(idx(j))
-    enddo
-    i  = i + nh + 1
-    nh = idx(i)
-    do j = i+1, i+nh
-      idx(j) = iperm(idx(j))
-    enddo
-    i = i + nh + 1
-    k = idx(i)
-  enddo
-
-end subroutine psi_renum_index
-
-subroutine psi_cnv_dsc(halo_in,ovrlap_in,ext_in,cdesc, info, mold)
-
-  use psi_mod, psi_protect_name =>  psi_cnv_dsc
-  use psb_realloc_mod
-  implicit none
-
-  !     ....scalars parameters....
-  integer(psb_ipk_), intent(in)                :: halo_in(:), ovrlap_in(:),ext_in(:)
-  type(psb_desc_type), intent(inout) :: cdesc
-  integer(psb_ipk_), intent(out)               :: info
-  class(psb_i_base_vect_type), optional, intent(in) :: mold
-
-  !     ....local scalars....      
-  integer(psb_ipk_) :: np,me
-  integer(psb_ipk_) :: ictxt, err_act,nxch,nsnd,nrcv,j,k
-  !     ...local array...
-  integer(psb_ipk_), allocatable  :: idx_out(:), tmp_mst_idx(:)
-
-  !     ...parameters
-  integer(psb_ipk_) :: debug_level, debug_unit
-  logical, parameter :: debug=.false.
-  character(len=20)  :: name
-
-  name='psi_cnv_desc'
-  call psb_get_erraction(err_act)
-  debug_level = psb_get_debug_level()
-  debug_unit  = psb_get_debug_unit()
-
-  info = psb_success_
-  ictxt = cdesc%get_context()
-
-  call psb_info(ictxt,me,np)
-  if (np == -1) then
-    info = psb_err_context_error_
-    call psb_errpush(info,name)
-    goto 9999
-  endif
-
-
-  ! first the halo index
-  if (debug_level>0) write(debug_unit,*) me,'Calling crea_index on halo',&
-       & size(halo_in)
-  call psi_crea_index(cdesc,halo_in, idx_out,.false.,nxch,nsnd,nrcv,info)
-  if (info /= psb_success_) then
-    call psb_errpush(psb_err_from_subroutine_,name,a_err='psi_crea_index')
-    goto 9999
-  end if
-  call psb_move_alloc(idx_out,cdesc%halo_index,info)
-
-  if (debug_level>0) write(debug_unit,*) me,'Done crea_index on halo'
-  if (debug_level>0) write(debug_unit,*) me,'Calling crea_index on ext'
-
-
-  ! then ext index
-  if (debug_level>0) write(debug_unit,*) me,'Calling crea_index on ext'
-  call psi_crea_index(cdesc,ext_in, idx_out,.false.,nxch,nsnd,nrcv,info)
-  if (info /= psb_success_) then
-    call psb_errpush(psb_err_from_subroutine_,name,a_err='psi_crea_index')
-    goto 9999
-  end if
-  call psb_move_alloc(idx_out,cdesc%ext_index,info)
-
-  if (debug_level>0) write(debug_unit,*) me,'Done crea_index on ext'
-  if (debug_level>0) write(debug_unit,*) me,'Calling crea_index on ovrlap'
-
-  ! then the overlap index
-  call psi_crea_index(cdesc,ovrlap_in, idx_out,.true.,nxch,nsnd,nrcv,info)
-  if (info /= psb_success_) then
-    call psb_errpush(psb_err_from_subroutine_,name,a_err='psi_crea_index')
-    goto 9999
-  end if
-  call psb_move_alloc(idx_out,cdesc%ovrlap_index,info)
-  if (info /= psb_success_) then
-    call psb_errpush(psb_err_from_subroutine_,name,a_err='psb_move_alloc')
-    goto 9999
-  end if
-
-
-  ! next  ovrlap_elem 
-  if (debug_level>0) write(debug_unit,*) me,'Calling crea_ovr_elem'
-  call psi_crea_ovr_elem(me,cdesc%ovrlap_index,cdesc%ovrlap_elem,info)
-  if (debug_level>0) write(debug_unit,*) me,'Done crea_ovr_elem'
-  if (info /= psb_success_) then
-    call psb_errpush(psb_err_from_subroutine_,name,a_err='psi_crea_ovr_elem')
-    goto 9999
-  end if
-  ! Extract ovr_mst_idx from ovrlap_elem 
-  if (debug_level>0) write(debug_unit,*) me,'Calling bld_ovr_mst'
-  call psi_bld_ovr_mst(me,cdesc%ovrlap_elem,tmp_mst_idx,info)
-  if (info == psb_success_) call psi_crea_index(cdesc,&
-       & tmp_mst_idx,idx_out,.false.,nxch,nsnd,nrcv,info)
-  if (debug_level>0) write(debug_unit,*) me,'Done crea_indx'
-  if (info /= psb_success_) then
-    call psb_errpush(psb_err_from_subroutine_,name,a_err='psi_bld_ovr_mst')
-    goto 9999
-  end if
-  call psb_move_alloc(idx_out,cdesc%ovr_mst_idx,info)
-  if (info /= psb_success_) then
-    call psb_errpush(psb_err_from_subroutine_,name,a_err='psb_move_alloc')
-    goto 9999
-  end if
-
-  ! finally bnd_elem
-  call psi_crea_bnd_elem(idx_out,cdesc,info)
-  if (info == psb_success_) call psb_move_alloc(idx_out,cdesc%bnd_elem,info)
-
-  call cdesc%v_halo_index%bld(cdesc%halo_index,mold=mold)
-  call cdesc%v_ext_index%bld(cdesc%ext_index,mold=mold)
-  call cdesc%v_ovrlap_index%bld(cdesc%ovrlap_index,mold=mold)
-  call cdesc%v_ovr_mst_idx%bld(cdesc%ovr_mst_idx,mold=mold)
-
-
-  if (info /= psb_success_) then
-    call psb_errpush(psb_err_from_subroutine_,name,a_err='psi_crea_bnd_elem')
-    goto 9999
-  end if
-  if (debug_level>0) write(debug_unit,*) me,'Done crea_bnd_elem'
-
-  call psb_erractionrestore(err_act)
-  return
+    ! then ext index
+    if (debug_level>0) write(debug_unit,*) me,'Calling crea_index on ext'
+    call psi_crea_index(cdesc,ext_in, idx_out,.false.,nxch,nsnd,nrcv,info)
+    if (info /= psb_success_) then
+      call psb_errpush(psb_err_from_subroutine_,name,a_err='psi_crea_index')
+      goto 9999
+    end if
+    call psb_move_alloc(idx_out,cdesc%ext_index,info)
+
+    if (debug_level>0) write(debug_unit,*) me,'Done crea_index on ext'
+    if (debug_level>0) write(debug_unit,*) me,'Calling crea_index on ovrlap'
+
+    ! then the overlap index
+    call psi_crea_index(cdesc,ovrlap_in, idx_out,.true.,nxch,nsnd,nrcv,info)
+    if (info /= psb_success_) then
+      call psb_errpush(psb_err_from_subroutine_,name,a_err='psi_crea_index')
+      goto 9999
+    end if
+    call psb_move_alloc(idx_out,cdesc%ovrlap_index,info)
+    if (info /= psb_success_) then
+      call psb_errpush(psb_err_from_subroutine_,name,a_err='psb_move_alloc')
+      goto 9999
+    end if
+
+
+    ! next  ovrlap_elem 
+    if (debug_level>0) write(debug_unit,*) me,'Calling crea_ovr_elem'
+    call psi_crea_ovr_elem(me,cdesc%ovrlap_index,cdesc%ovrlap_elem,info)
+    if (debug_level>0) write(debug_unit,*) me,'Done crea_ovr_elem'
+    if (info /= psb_success_) then
+      call psb_errpush(psb_err_from_subroutine_,name,a_err='psi_crea_ovr_elem')
+      goto 9999
+    end if
+    ! Extract ovr_mst_idx from ovrlap_elem 
+    if (debug_level>0) write(debug_unit,*) me,'Calling bld_ovr_mst'
+    call psi_bld_ovr_mst(me,cdesc%ovrlap_elem,tmp_mst_idx,info)
+    if (info == psb_success_) call psi_crea_index(cdesc,&
+         & tmp_mst_idx,idx_out,.false.,nxch,nsnd,nrcv,info)
+    if (debug_level>0) write(debug_unit,*) me,'Done crea_indx'
+    if (info /= psb_success_) then
+      call psb_errpush(psb_err_from_subroutine_,name,a_err='psi_bld_ovr_mst')
+      goto 9999
+    end if
+    call psb_move_alloc(idx_out,cdesc%ovr_mst_idx,info)
+    if (info /= psb_success_) then
+      call psb_errpush(psb_err_from_subroutine_,name,a_err='psb_move_alloc')
+      goto 9999
+    end if
+
+    ! finally bnd_elem
+    call psi_crea_bnd_elem(idx_out,cdesc,info)
+    if (info == psb_success_) call psb_move_alloc(idx_out,cdesc%bnd_elem,info)
+
+    call cdesc%v_halo_index%bld(cdesc%halo_index,mold=mold)
+    call cdesc%v_ext_index%bld(cdesc%ext_index,mold=mold)
+    call cdesc%v_ovrlap_index%bld(cdesc%ovrlap_index,mold=mold)
+    call cdesc%v_ovr_mst_idx%bld(cdesc%ovr_mst_idx,mold=mold)
+
+
+    if (info /= psb_success_) then
+      call psb_errpush(psb_err_from_subroutine_,name,a_err='psi_crea_bnd_elem')
+      goto 9999
+    end if
+    if (debug_level>0) write(debug_unit,*) me,'Done crea_bnd_elem'
+
+    call psb_erractionrestore(err_act)
+    return
 
 9999 call psb_error_handler(ictxt,err_act)
 
-  return
-
-end subroutine psi_cnv_dsc
-
-
-subroutine psi_inner_cnvs(x,hashmask,hashv,glb_lc)
-  use psi_mod, psi_protect_name => psi_inner_cnvs
-
-  integer(psb_ipk_), intent(in)    :: hashmask,hashv(0:),glb_lc(:,:)
-  integer(psb_ipk_), intent(inout) :: x
-
-  integer(psb_ipk_) :: i, ih, key, idx,nh,tmp,lb,ub,lm
-  !
-  ! When a large descriptor is assembled the indices 
-  ! are kept in a (hashed) list of ordered lists. 
-  ! Thus we first hash the index, then we do a binary search on the 
-  ! ordered sublist. The hashing is based on the low-order bits 
-  ! for a width of psb_hash_bits 
-  !
-
-  key = x
-  ih  = iand(key,hashmask)
-  idx = hashv(ih)
-  nh  = hashv(ih+1) - hashv(ih) 
-  if (nh > 0) then 
-    tmp = -1 
-    lb = idx
-    ub = idx+nh-1
-    do 
-      if (lb>ub) exit
-      lm = (lb+ub)/2
-      if (key == glb_lc(lm,1)) then 
-        tmp = lm
-        exit
-      else if (key<glb_lc(lm,1)) then 
-        ub = lm - 1
-      else
-        lb = lm + 1
-      end if
-    end do
-  else 
-    tmp = -1
-  end if
-  if (tmp > 0) then 
-    x = glb_lc(tmp,2)
-  else         
-    x = tmp 
-  end if
-end subroutine psi_inner_cnvs
-
-subroutine psi_inner_cnvs2(x,y,hashmask,hashv,glb_lc)
-  use psi_mod, psi_protect_name =>  psi_inner_cnvs2
-  integer(psb_ipk_), intent(in)  :: hashmask,hashv(0:),glb_lc(:,:)
-  integer(psb_ipk_), intent(in)  :: x
-  integer(psb_ipk_), intent(out) :: y
-
-  integer(psb_ipk_) :: i, ih, key, idx,nh,tmp,lb,ub,lm
-  !
-  ! When a large descriptor is assembled the indices 
-  ! are kept in a (hashed) list of ordered lists. 
-  ! Thus we first hash the index, then we do a binary search on the 
-  ! ordered sublist. The hashing is based on the low-order bits 
-  ! for a width of psb_hash_bits 
-  !
-
-  key = x
-  ih  = iand(key,hashmask)
-  idx = hashv(ih)
-  nh  = hashv(ih+1) - hashv(ih) 
-  if (nh > 0) then 
-    tmp = -1 
-    lb = idx
-    ub = idx+nh-1
-    do 
-      if (lb>ub) exit
-      lm = (lb+ub)/2
-      if (key == glb_lc(lm,1)) then 
-        tmp = lm
-        exit
-      else if (key<glb_lc(lm,1)) then 
-        ub = lm - 1
-      else
-        lb = lm + 1
-      end if
-    end do
-  else 
-    tmp = -1
-  end if
-  if (tmp > 0) then 
-    y = glb_lc(tmp,2)
-  else         
-    y = tmp 
-  end if
-end subroutine psi_inner_cnvs2
-
-
-subroutine psi_inner_cnv1(n,x,hashmask,hashv,glb_lc,mask)
-  use psi_mod, psi_protect_name =>  psi_inner_cnv1
-  integer(psb_ipk_), intent(in)    :: n,hashmask,hashv(0:),glb_lc(:,:)
-  logical, intent(in), optional    :: mask(:)
-  integer(psb_ipk_), intent(inout) :: x(:)
-
-  integer(psb_ipk_) :: i, ih, key, idx,nh,tmp,lb,ub,lm
-  !
-  ! When a large descriptor is assembled the indices 
-  ! are kept in a (hashed) list of ordered lists. 
-  ! Thus we first hash the index, then we do a binary search on the 
-  ! ordered sublist. The hashing is based on the low-order bits 
-  ! for a width of psb_hash_bits 
-  !
-  if (present(mask)) then 
-    do i=1, n
-      if (mask(i)) then 
+    return
+
+  end subroutine psi_cnv_dsc
+
+
+  subroutine psi_inner_cnvs(x,hashmask,hashv,glb_lc)
+
+    integer(psb_ipk_), intent(in)    :: hashmask,hashv(0:),glb_lc(:,:)
+    integer(psb_ipk_), intent(inout) :: x
+
+    integer(psb_ipk_) :: i, ih, key, idx,nh,tmp,lb,ub,lm
+    !
+    ! When a large descriptor is assembled the indices 
+    ! are kept in a (hashed) list of ordered lists. 
+    ! Thus we first hash the index, then we do a binary search on the 
+    ! ordered sublist. The hashing is based on the low-order bits 
+    ! for a width of psb_hash_bits 
+    !
+
+    key = x
+    ih  = iand(key,hashmask)
+    idx = hashv(ih)
+    nh  = hashv(ih+1) - hashv(ih) 
+    if (nh > 0) then 
+      tmp = -1 
+      lb = idx
+      ub = idx+nh-1
+      do 
+        if (lb>ub) exit
+        lm = (lb+ub)/2
+        if (key == glb_lc(lm,1)) then 
+          tmp = lm
+          exit
+        else if (key<glb_lc(lm,1)) then 
+          ub = lm - 1
+        else
+          lb = lm + 1
+        end if
+      end do
+    else 
+      tmp = -1
+    end if
+    if (tmp > 0) then 
+      x = glb_lc(tmp,2)
+    else         
+      x = tmp 
+    end if
+  end subroutine psi_inner_cnvs
+
+  subroutine psi_inner_cnvs2(x,y,hashmask,hashv,glb_lc)
+    integer(psb_ipk_), intent(in)  :: hashmask,hashv(0:),glb_lc(:,:)
+    integer(psb_ipk_), intent(in)  :: x
+    integer(psb_ipk_), intent(out) :: y
+
+    integer(psb_ipk_) :: i, ih, key, idx,nh,tmp,lb,ub,lm
+    !
+    ! When a large descriptor is assembled the indices 
+    ! are kept in a (hashed) list of ordered lists. 
+    ! Thus we first hash the index, then we do a binary search on the 
+    ! ordered sublist. The hashing is based on the low-order bits 
+    ! for a width of psb_hash_bits 
+    !
+
+    key = x
+    ih  = iand(key,hashmask)
+    idx = hashv(ih)
+    nh  = hashv(ih+1) - hashv(ih) 
+    if (nh > 0) then 
+      tmp = -1 
+      lb = idx
+      ub = idx+nh-1
+      do 
+        if (lb>ub) exit
+        lm = (lb+ub)/2
+        if (key == glb_lc(lm,1)) then 
+          tmp = lm
+          exit
+        else if (key<glb_lc(lm,1)) then 
+          ub = lm - 1
+        else
+          lb = lm + 1
+        end if
+      end do
+    else 
+      tmp = -1
+    end if
+    if (tmp > 0) then 
+      y = glb_lc(tmp,2)
+    else         
+      y = tmp 
+    end if
+  end subroutine psi_inner_cnvs2
+
+
+  subroutine psi_inner_cnv1(n,x,hashmask,hashv,glb_lc,mask)
+    integer(psb_ipk_), intent(in)    :: n,hashmask,hashv(0:),glb_lc(:,:)
+    logical, intent(in), optional    :: mask(:)
+    integer(psb_ipk_), intent(inout) :: x(:)
+
+    integer(psb_ipk_) :: i, ih, key, idx,nh,tmp,lb,ub,lm
+    !
+    ! When a large descriptor is assembled the indices 
+    ! are kept in a (hashed) list of ordered lists. 
+    ! Thus we first hash the index, then we do a binary search on the 
+    ! ordered sublist. The hashing is based on the low-order bits 
+    ! for a width of psb_hash_bits 
+    !
+    if (present(mask)) then 
+      do i=1, n
+        if (mask(i)) then 
+          key = x(i) 
+          ih  = iand(key,hashmask)
+          idx = hashv(ih)
+          nh  = hashv(ih+1) - hashv(ih) 
+          if (nh > 0) then 
+            tmp = -1 
+            lb = idx
+            ub = idx+nh-1
+            do 
+              if (lb>ub) exit
+              lm = (lb+ub)/2
+              if (key == glb_lc(lm,1)) then 
+                tmp = lm
+                exit
+              else if (key<glb_lc(lm,1)) then 
+                ub = lm - 1
+              else
+                lb = lm + 1
+              end if
+            end do
+          else 
+            tmp = -1
+          end if
+          if (tmp > 0) then 
+            x(i) = glb_lc(tmp,2)
+          else         
+            x(i) = tmp 
+          end if
+        end if
+      end do
+    else
+      do i=1, n
         key = x(i) 
         ih  = iand(key,hashmask)
         idx = hashv(ih)
@@ -324,60 +353,62 @@ subroutine psi_inner_cnv1(n,x,hashmask,hashv,glb_lc,mask)
         else         
           x(i) = tmp 
         end if
-      end if
-    end do
-  else
-    do i=1, n
-      key = x(i) 
-      ih  = iand(key,hashmask)
-      idx = hashv(ih)
-      nh  = hashv(ih+1) - hashv(ih) 
-      if (nh > 0) then 
-        tmp = -1 
-        lb = idx
-        ub = idx+nh-1
-        do 
-          if (lb>ub) exit
-          lm = (lb+ub)/2
-          if (key == glb_lc(lm,1)) then 
-            tmp = lm
-            exit
-          else if (key<glb_lc(lm,1)) then 
-            ub = lm - 1
-          else
-            lb = lm + 1
+      end do
+    end if
+  end subroutine psi_inner_cnv1
+
+  subroutine psi_inner_cnv2(n,x,y,hashmask,hashv,glb_lc,mask)
+    integer(psb_ipk_), intent(in)  :: n, hashmask,hashv(0:),glb_lc(:,:)
+    logical, intent(in),optional  :: mask(:)
+    integer(psb_ipk_), intent(in)  :: x(:)
+    integer(psb_ipk_), intent(out) :: y(:)
+
+    integer(psb_ipk_) :: i, ih, key, idx,nh,tmp,lb,ub,lm
+    !
+    ! When a large descriptor is assembled the indices 
+    ! are kept in a (hashed) list of ordered lists. 
+    ! Thus we first hash the index, then we do a binary search on the 
+    ! ordered sublist. The hashing is based on the low-order bits 
+    ! for a width of psb_hash_bits 
+    !
+    if (present(mask)) then 
+      do i=1, n
+        if (mask(i)) then 
+          key = x(i) 
+          ih  = iand(key,hashmask)
+          if (ih > ubound(hashv,1) ) then 
+            write(psb_err_unit,*) ' In inner cnv: ',ih,ubound(hashv)
           end if
-        end do
-      else 
-        tmp = -1
-      end if
-      if (tmp > 0) then 
-        x(i) = glb_lc(tmp,2)
-      else         
-        x(i) = tmp 
-      end if
-    end do
-  end if
-end subroutine psi_inner_cnv1
-
-subroutine psi_inner_cnv2(n,x,y,hashmask,hashv,glb_lc,mask)
-  use psi_mod, psi_protect_name =>  psi_inner_cnv2
-  integer(psb_ipk_), intent(in)  :: n, hashmask,hashv(0:),glb_lc(:,:)
-  logical, intent(in),optional  :: mask(:)
-  integer(psb_ipk_), intent(in)  :: x(:)
-  integer(psb_ipk_), intent(out) :: y(:)
-
-  integer(psb_ipk_) :: i, ih, key, idx,nh,tmp,lb,ub,lm
-  !
-  ! When a large descriptor is assembled the indices 
-  ! are kept in a (hashed) list of ordered lists. 
-  ! Thus we first hash the index, then we do a binary search on the 
-  ! ordered sublist. The hashing is based on the low-order bits 
-  ! for a width of psb_hash_bits 
-  !
-  if (present(mask)) then 
-    do i=1, n
-      if (mask(i)) then 
+          idx = hashv(ih)
+          nh  = hashv(ih+1) - hashv(ih) 
+          if (nh > 0) then 
+            tmp = -1 
+            lb = idx
+            ub = idx+nh-1
+            do 
+              if (lb>ub) exit
+              lm = (lb+ub)/2
+              if (key == glb_lc(lm,1)) then 
+                tmp = lm
+                exit
+              else if (key<glb_lc(lm,1)) then 
+                ub = lm - 1
+              else
+                lb = lm + 1
+              end if
+            end do
+          else 
+            tmp = -1
+          end if
+          if (tmp > 0) then 
+            y(i) = glb_lc(tmp,2)
+          else         
+            y(i) = tmp 
+          end if
+        end if
+      end do
+    else
+      do i=1, n
         key = x(i) 
         ih  = iand(key,hashmask)
         if (ih > ubound(hashv,1) ) then 
@@ -409,89 +440,54 @@ subroutine psi_inner_cnv2(n,x,y,hashmask,hashv,glb_lc,mask)
         else         
           y(i) = tmp 
         end if
+      end do
+    end if
+  end subroutine psi_inner_cnv2
+
+  subroutine psi_bld_ovr_mst(me,ovrlap_elem,mst_idx,info)
+
+    use psb_realloc_mod
+    implicit none
+
+    !     ....scalars parameters....
+    integer(psb_ipk_), intent(in)               :: me, ovrlap_elem(:,:)
+    integer(psb_ipk_), allocatable, intent(out) :: mst_idx(:) 
+    integer(psb_ipk_), intent(out)              :: info
+
+    integer(psb_ipk_) :: i, j, proc, nov,isz, ip, err_act, idx
+    character(len=20)  :: name
+
+    name='psi_bld_ovr_mst'
+    call psb_get_erraction(err_act)
+
+    nov = size(ovrlap_elem,1)
+    isz = 3*nov+1
+    call psb_realloc(isz,mst_idx,info) 
+    if (info /= psb_success_) then
+      call psb_errpush(psb_err_internal_error_,name,a_err='reallocate')
+      goto 9999
+    end if
+    mst_idx = -1
+    j = 1
+    do i=1, nov
+      proc = ovrlap_elem(i,3)
+      if (me /= proc) then 
+        idx = ovrlap_elem(i,1)
+        mst_idx(j+0) = proc
+        mst_idx(j+1) = 1
+        mst_idx(j+2) = idx
+        j = j + 3
       end if
     end do
-  else
-    do i=1, n
-      key = x(i) 
-      ih  = iand(key,hashmask)
-      if (ih > ubound(hashv,1) ) then 
-        write(psb_err_unit,*) ' In inner cnv: ',ih,ubound(hashv)
-      end if
-      idx = hashv(ih)
-      nh  = hashv(ih+1) - hashv(ih) 
-      if (nh > 0) then 
-        tmp = -1 
-        lb = idx
-        ub = idx+nh-1
-        do 
-          if (lb>ub) exit
-          lm = (lb+ub)/2
-          if (key == glb_lc(lm,1)) then 
-            tmp = lm
-            exit
-          else if (key<glb_lc(lm,1)) then 
-            ub = lm - 1
-          else
-            lb = lm + 1
-          end if
-        end do
-      else 
-        tmp = -1
-      end if
-      if (tmp > 0) then 
-        y(i) = glb_lc(tmp,2)
-      else         
-        y(i) = tmp 
-      end if
-    end do
-  end if
-end subroutine psi_inner_cnv2
-
-subroutine psi_bld_ovr_mst(me,ovrlap_elem,mst_idx,info)
-  use psi_mod, psi_protect_name =>  psi_bld_ovr_mst
-
-  use psb_realloc_mod
-  implicit none
-
-  !     ....scalars parameters....
-  integer(psb_ipk_), intent(in)               :: me, ovrlap_elem(:,:)
-  integer(psb_ipk_), allocatable, intent(out) :: mst_idx(:) 
-  integer(psb_ipk_), intent(out)              :: info
-
-  integer(psb_ipk_) :: i, j, proc, nov,isz, ip, err_act, idx
-  character(len=20)  :: name
-
-  name='psi_bld_ovr_mst'
-  call psb_get_erraction(err_act)
-
-  nov = size(ovrlap_elem,1)
-  isz = 3*nov+1
-  call psb_realloc(isz,mst_idx,info) 
-  if (info /= psb_success_) then
-    call psb_errpush(psb_err_internal_error_,name,a_err='reallocate')
-    goto 9999
-  end if
-  mst_idx = -1
-  j = 1
-  do i=1, nov
-    proc = ovrlap_elem(i,3)
-    if (me /= proc) then 
-      idx = ovrlap_elem(i,1)
-      mst_idx(j+0) = proc
-      mst_idx(j+1) = 1
-      mst_idx(j+2) = idx
-      j = j + 3
-    end if
-  end do
-  mst_idx(j) = -1 
+    mst_idx(j) = -1 
 
-  call psb_erractionrestore(err_act)
-  return  
+    call psb_erractionrestore(err_act)
+    return  
 
 9999 call psb_error_handler(err_act)
 
-  return
+    return
 
-end subroutine psi_bld_ovr_mst
+  end subroutine psi_bld_ovr_mst
 
+end submodule psi_desc_impl_mod