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[/] [openrisc/] [trunk/] [gnu-dev/] [or1k-gcc/] [gcc/] [ada/] [s-strhas.adb] - Blame information for rev 706

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1 706 jeremybenn
------------------------------------------------------------------------------
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--                                                                          --
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--                         GNAT COMPILER COMPONENTS                         --
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--                                                                          --
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--                    S Y S T E M . S T R I N G _ H A S H                   --
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--                                                                          --
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--                                 S p e c                                  --
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--                                                                          --
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--             Copyright (C) 2009, Free Software Foundation, Inc.           --
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--                                                                          --
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-- GNAT is free software;  you can  redistribute it  and/or modify it under --
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-- terms of the  GNU General Public License as published  by the Free Soft- --
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-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
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-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
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--                                                                          --
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-- As a special exception under Section 7 of GPL version 3, you are granted --
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-- additional permissions described in the GCC Runtime Library Exception,   --
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-- version 3.1, as published by the Free Software Foundation.               --
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--                                                                          --
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-- You should have received a copy of the GNU General Public License and    --
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-- a copy of the GCC Runtime Library Exception along with this program;     --
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-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
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-- <http://www.gnu.org/licenses/>.                                          --
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--                                                                          --
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-- GNAT was originally developed  by the GNAT team at  New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc.      --
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--                                                                          --
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------------------------------------------------------------------------------
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pragma Compiler_Unit;
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package body System.String_Hash is
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   --  Compute a hash value for a key. The approach here is follows the
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   --  algorithm used in GNU Awk and the ndbm substitute SDBM by Ozan Yigit.
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   ----------
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   -- Hash --
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   ----------
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   function Hash (Key : Key_Type) return Hash_Type is
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      pragma Compile_Time_Error
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        (Hash_Type'Modulus /= 2 ** 32
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          or else Hash_Type'First /= 0
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          or else Hash_Type'Last /= 2 ** 32 - 1,
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         "Hash_Type must be 32-bit modular with range 0 .. 2**32-1");
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      function Shift_Left
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        (Value  : Hash_Type;
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         Amount : Natural) return Hash_Type;
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      pragma Import (Intrinsic, Shift_Left);
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      H : Hash_Type;
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   begin
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      H := 0;
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      for J in Key'Range loop
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         H := Char_Type'Pos (Key (J))
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                + Shift_Left (H, 6) + Shift_Left (H, 16) - H;
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      end loop;
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      return H;
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   end Hash;
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end System.String_Hash;

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