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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) 2009-2013, 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_Warning;
+
+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;