gcc/ada/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) 2004-2006, 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 2,  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.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  19 -- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
  20 -- Boston, MA 02110-1301, USA.                                              --
  21 --                                                                          --
  22 -- As a special exception,  if other files  instantiate  generics from this --
  23 -- unit, or you link  this unit with other files  to produce an executable, --
  24 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  25 -- covered  by the  GNU  General  Public  License.  This exception does not --
  26 -- however invalidate  any other reasons why  the executable file  might be --
  27 -- covered by the  GNU Public License.                                      --
  28 --                                                                          --
  29 -- This unit was originally developed by Matthew J Heaney.                  --
  30 ------------------------------------------------------------------------------
  31
  32 package body Ada.Containers.Prime_Numbers is
  33
  34    --------------
  35    -- To_Prime --
  36    --------------
  37
  38    function To_Prime (Length : Count_Type) return Hash_Type is
  39       I, J, K : Integer'Base;
  40       Index   : Integer'Base;
  41
  42    begin
  43       I := Primes'Last - Primes'First;
  44       Index := Primes'First;
  45       while I > 0 loop
  46          J := I / 2;
  47          K := Index + J;
  48
  49          if Primes (K) < Hash_Type (Length) then
  50             Index := K + 1;
  51             I := I - J - 1;
  52          else
  53             I := J;
  54          end if;
  55       end loop;
  56
  57       return Primes (Index);
  58    end To_Prime;
  59
  60 end Ada.Containers.Prime_Numbers;