## Copyright (C) 2004-2011 David Bateman
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 3 of the License, or (at
## your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, see
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn {Function File} {@var{y} =} circshift (@var{x}, @var{n})
## Circularly shift the values of the array @var{x}.  @var{n} must be
## a vector of integers no longer than the number of dimensions in
## @var{x}.  The values of @var{n} can be either positive or negative,
## which determines the direction in which the values or @var{x} are
## shifted.  If an element of @var{n} is zero, then the corresponding
## dimension of @var{x} will not be shifted.  For example:
##
## @example
## @group
## x = [1, 2, 3; 4, 5, 6; 7, 8, 9];
## circshift (x, 1)
## @result{}  7, 8, 9
##     1, 2, 3
##     4, 5, 6
## circshift (x, -2)
## @result{}  7, 8, 9
##     1, 2, 3
##     4, 5, 6
## circshift (x, [0,1])
## @result{}  3, 1, 2
##     6, 4, 5
##     9, 7, 8
## @end group
## @end example
## @seealso {permute, ipermute, shiftdim}
## @end deftypefn

function y = circshift (x, n)

  if (nargin == 2)
    if (isempty (x))
      y = x;
    else
      nd = ndims (x);
      sz = size (x);

      if (! isvector (n) && length (n) > nd)
        error ("circshift: N must be a vector, no longer than the number of dimension in X");
      endif

      if (any (n != floor (n)))
        error ("circshift: all values of N must be integers");
      endif

      idx = cell ();
      for i = 1:length (n);
        nn = n(i);
        if (nn < 0)
          while (sz(i) <= -nn)
            nn = nn + sz(i);
          endwhile
          idx{i} = [(1-nn):sz(i), 1:-nn];
        else
          while (sz(i) <= nn)
            nn = nn - sz(i);
          endwhile
          idx{i} = [(sz(i)-nn+1):sz(i), 1:(sz(i)-nn)];
        endif
      endfor
      for i = (length(n) + 1) : nd
        idx{i} = 1:sz(i);
      endfor
      y = x(idx{:});
    endif
  else
    print_usage ();
  endif
endfunction

%!shared x
%! x = [1, 2, 3; 4, 5, 6; 7, 8, 9];

%!assert (circshift (x, 1), [7, 8, 9; 1, 2, 3; 4, 5, 6])
%!assert (circshift (x, -2), [7, 8, 9; 1, 2, 3; 4, 5, 6])
%!assert (circshift (x, [0, 1]), [3, 1, 2; 6, 4, 5; 9, 7, 8]);
%!assert (circshift ([],1), [])

%!assert (full (circshift (eye (3), 1)), circshift (full (eye (3)), 1))
%!assert (full (circshift (eye (3), 1)), [0,0,1;1,0,0;0,1,0])