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annotate scripts/specfun/isprime.m @ 19233:0976f9fccbbd

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isprime.m: Verify that input is a real number (bug #43041) * isprime.m: Use isreal() to validate input. Put input checking first in function. Add input validation tests.
author Rik <rik@octave.org>
date Thu, 21 Aug 2014 16:05:09 -0700
parents d63878346099
children 920a400929ca
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rev   line source
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d63878346099 maint: Update copyright notices for release.
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1 ## Copyright (C) 2000-2013 Paul Kienzle
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2 ## Copyright (C) 2010 VZLU Prague
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3 ##
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4 ## This file is part of Octave.
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5 ##
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6 ## Octave is free software; you can redistribute it and/or modify it
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7 ## under the terms of the GNU General Public License as published by
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8 ## the Free Software Foundation; either version 3 of the License, or (at
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9 ## your option) any later version.
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10 ##
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11 ## Octave is distributed in the hope that it will be useful, but
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12 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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13 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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14 ## General Public License for more details.
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15 ##
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16 ## You should have received a copy of the GNU General Public License
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17 ## along with Octave; see the file COPYING. If not, see
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18 ## <http://www.gnu.org/licenses/>.
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19
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20 ## -*- texinfo -*-
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21 ## @deftypefn {Function File} {} isprime (@var{x})
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22 ## Return a logical array which is true where the elements of @var{x} are
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23 ## prime numbers and false where they are not.
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24 ##
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25 ## @code{isprime} is appropriate if the maximum value in @var{x} is not too
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26 ## large (< 1e15). For larger values special purpose factorization code
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27 ## should be used.
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28 ##
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29 ## @example
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30 ## @group
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31 ## isprime (1:6)
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32 ## @result{} [0, 1, 1, 0, 1, 0]
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33 ## @end group
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34 ## @end example
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35 ## @seealso{primes, factor, gcd, lcm}
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36 ## @end deftypefn
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37
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38 function t = isprime (x)
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39
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40 if (nargin != 1)
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41 print_usage ();
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42 elseif (! isreal (x) || any ((x < 0 | x != fix (x))(:)))
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43 error ("isprime: X must be a non-negative integer");
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44 endif
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45
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46 maxn = max (x(:));
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47 ## generate prime table of suitable length.
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48 maxp = min (maxn, max (sqrt (maxn), 1e7)); # FIXME: threshold not optimized.
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49 pr = primes (maxp);
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50 ## quick search for table matches.
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51 t = lookup (pr, x, "b");
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52 ## take the rest.
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53 m = x(x > maxp);
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54 if (! isempty (m))
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55 ## there are still possible primes. filter them out by division.
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56 if (maxn <= intmax ("uint32"))
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57 m = uint32 (m);
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58 elseif (maxn <= intmax ("uint64"))
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59 m = uint64 (m);
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60 else
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61 warning ("isprime: X contains integers too large to be tested");
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62 endif
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63 pr = cast (pr(pr <= sqrt (maxn)), class (m));
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64 for p = pr
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65 m = m(rem (m, p) != 0);
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66 if (length (m) < length (pr) / 10)
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67 break;
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68 endif
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69 endfor
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70 pr = pr(pr > p);
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71 mm = arrayfun (@(x) all (rem (x, pr)), m);
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72 m = m(mm);
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73 if (! isempty (m))
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74 m = cast (sort (m), class (x));
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75 t |= lookup (m, x, "b");
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76 endif
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77 endif
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78
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79 endfunction
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80
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81
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82 %!assert (isprime (3), true)
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83 %!assert (isprime (4), false)
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84 %!assert (isprime (magic (3)), logical ([0, 0, 0; 1, 1, 1; 0, 0, 1]))
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85
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86 %% Test input validation
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87 %!error isprime ()
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88 %!error isprime (1, 2)
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89 %!error <X must be a non-negative integer> isprime (i)
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90 %!error <X must be a non-negative integer> isprime ([1 2; -3 4])
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91 %!error <X must be a non-negative integer> isprime ([1 2; 3.1 4])
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92