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   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 --                                 S p e c                                  --
   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 --  This package declares the prime numbers array used to implement hashed
  33 --  containers. Bucket arrays are always allocated with a prime-number
  34 --  length (computed using To_Prime below), as this produces better scatter
  35 --  when hash values are folded.
  36
  37 package Ada.Containers.Prime_Numbers is
  38    pragma Pure;
  39
  40    type Primes_Type is array (Positive range <>) of Hash_Type;
  41
  42    Primes : constant Primes_Type :=
  43      (53,         97,         193,       389,       769,
  44       1543,       3079,       6151,      12289,     24593,
  45       49157,      98317,      196613,    393241,    786433,
  46       1572869,    3145739,    6291469,   12582917,  25165843,
  47       50331653,   100663319,  201326611, 402653189, 805306457,
  48       1610612741, 3221225473, 4294967291);
  49
  50    function To_Prime (Length : Count_Type) return Hash_Type;
  51    --  Returns the smallest value in Primes not less than Length
  52
  53 end Ada.Containers.Prime_Numbers;