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[/] [openrisc/] [trunk/] [gnu-src/] [gcc-4.5.1/] [gcc/] [ada/] [s-strhas.adb] - Rev 288
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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;
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