File : a-coprnu.adb
1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT LIBRARY COMPONENTS --
4 -- --
5 -- A D A . C O N T A I N E R S . P R I M E _ N U M B E R S --
6 -- --
7 -- B o d y --
8 -- --
9 -- Copyright (C) 2004-2009, Free Software Foundation, Inc. --
10 -- --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 3, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
17 -- --
18 -- --
19 -- --
20 -- --
21 -- --
22 -- You should have received a copy of the GNU General Public License and --
23 -- a copy of the GCC Runtime Library Exception along with this program; --
24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
25 -- <http://www.gnu.org/licenses/>. --
26 -- --
27 -- This unit was originally developed by Matthew J Heaney. --
28 ------------------------------------------------------------------------------
29
30 package body Ada.Containers.Prime_Numbers is
31
32 --------------
33 -- To_Prime --
34 --------------
35
36 function To_Prime (Length : Count_Type) return Hash_Type is
37 I, J, K : Integer'Base;
38 Index : Integer'Base;
39
40 begin
41 I := Primes'Last - Primes'First;
42 Index := Primes'First;
43 while I > 0 loop
44 J := I / 2;
45 K := Index + J;
46
47 if Primes (K) < Hash_Type (Length) then
48 Index := K + 1;
49 I := I - J - 1;
50 else
51 I := J;
52 end if;
53 end loop;
54
55 return Primes (Index);
56 end To_Prime;
57
58 end Ada.Containers.Prime_Numbers;