--- /dev/null
+## Copyright (C) 2000-2012 Paul Kienzle
+## Copyright (C) 2010 VZLU Prague
+##
+## 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} {} isprime (@var{x})
+## Return a logical array which is true where the elements of @var{x} are
+## prime numbers and false where they are not.
+##
+## If the maximum value in @var{x} is very large, then you should be using
+## special purpose factorization code.
+##
+## @example
+## @group
+## isprime (1:6)
+## @result{} [0, 1, 1, 0, 1, 0]
+## @end group
+## @end example
+## @seealso{primes, factor, gcd, lcm}
+## @end deftypefn
+
+function t = isprime (x)
+
+ if (nargin == 1)
+ if (any ((x != floor (x) | x < 0)(:)))
+ error ("isprime: needs positive integers");
+ endif
+ maxn = max (x(:));
+ ## generate prime table of suitable length.
+ maxp = min (maxn, max (sqrt (maxn), 1e7)); # FIXME: threshold not optimized.
+ pr = primes (maxp);
+ ## quick search for table matches.
+ t = lookup (pr, x, "b");
+ ## take the rest.
+ m = x(x > maxp);
+ if (! isempty (m))
+ ## there are still possible primes. filter them out by division.
+ if (maxn <= intmax ("uint32"))
+ m = uint32 (m);
+ elseif (maxn <= intmax ("uint64"))
+ m = uint64 (m);
+ else
+ warning ("isprime: too large integers being tested");
+ endif
+ pr = cast (pr(pr <= sqrt (maxn)), class (m));
+ for p = pr
+ m = m(rem (m, p) != 0);
+ if (length (m) < length (pr) / 10)
+ break;
+ endif
+ endfor
+ pr = pr(pr > p);
+ mm = arrayfun (@(x) all (rem (x, pr)), m);
+ m = m(mm);
+ if (! isempty (m))
+ m = cast (sort (m), class (x));
+ t |= lookup (m, x, "b");
+ endif
+ endif
+
+ else
+ print_usage ();
+ endif
+
+endfunction
+
+
+%!assert (isprime (4), logical (0));
+%!assert (isprime (3), logical (1));
+%!assert (isprime (magic (3)), logical ([0, 0, 0; 1, 1, 1; 0, 0, 1]));
+%!error isprime ()
+%!error isprime (1, 2)