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------------------------------------------------------------------------------

--                                                                          --

--                         GNAT COMPILER COMPONENTS                         --

--                                                                          --

--                    S Y S T E M . S T R I N G _ H A S H                   --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--             Copyright (C) 2009, Free Software Foundation, Inc.           --

--                                                                          --

-- GNAT is free software;  you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 3,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --

--                                                                          --

-- As a special exception under Section 7 of GPL version 3, you are granted --

-- additional permissions described in the GCC Runtime Library Exception,   --

-- version 3.1, as published by the Free Software Foundation.               --

--                                                                          --

-- You should have received a copy of the GNU General Public License and    --

-- a copy of the GCC Runtime Library Exception along with this program;     --

-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --

-- <http://www.gnu.org/licenses/>.                                          --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

------------------------------------------------------------------------------

pragma Compiler_Unit;

package body System.String_Hash is

   --  Compute a hash value for a key. The approach here is follows the

   --  algorithm used in GNU Awk and the ndbm substitute SDBM by Ozan Yigit.

   ----------

   -- Hash --

   ----------

   function Hash (Key : Key_Type) return Hash_Type is

      pragma Compile_Time_Error

        (Hash_Type'Modulus /= 2 ** 32

          or else Hash_Type'First /= 0

          or else Hash_Type'Last /= 2 ** 32 - 1,

         "Hash_Type must be 32-bit modular with range 0 .. 2**32-1");

      function Shift_Left

        (Value  : Hash_Type;

         Amount : Natural) return Hash_Type;

      pragma Import (Intrinsic, Shift_Left);

      H : Hash_Type;

   begin

      H := 0;

      for J in Key'Range loop

         H := Char_Type'Pos (Key (J))

                + Shift_Left (H, 6) + Shift_Left (H, 16) - H;

      end loop;

      return H;

   end Hash;

end System.String_Hash;