## Copyright (C) 2004 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 2, 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, write to the Free
## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
## 02110-1301, USA.

## -*- texinfo -*-
## @deftypefn {Function File} {@var{y}} = circshift (@var{x}, @var{n})
## Circularly shifts 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)
    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{:});
  else
    usage ("circshift (x, n)");
  endif
endfunction