1------------------------------------------------------------------------------ 2-- -- 3-- GNAT COMPILER COMPONENTS -- 4-- -- 5-- S Y S T E M . S T R I N G _ H A S H -- 6-- -- 7-- S p e c -- 8-- -- 9-- Copyright (C) 2009-2013, 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 3, 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. -- 17-- -- 18-- As a special exception under Section 7 of GPL version 3, you are granted -- 19-- additional permissions described in the GCC Runtime Library Exception, -- 20-- version 3.1, as published by the Free Software Foundation. -- 21-- -- 22-- You should have received a copy of the GNU General Public License and -- 23-- a copy of the GCC Runtime Library Exception along with this program; -- 24-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see -- 25-- <http://www.gnu.org/licenses/>. -- 26-- -- 27-- GNAT was originally developed by the GNAT team at New York University. -- 28-- Extensive contributions were provided by Ada Core Technologies Inc. -- 29-- -- 30------------------------------------------------------------------------------ 31 32pragma Compiler_Unit_Warning; 33 34package body System.String_Hash is 35 36 -- Compute a hash value for a key. The approach here is follows the 37 -- algorithm used in GNU Awk and the ndbm substitute SDBM by Ozan Yigit. 38 39 ---------- 40 -- Hash -- 41 ---------- 42 43 function Hash (Key : Key_Type) return Hash_Type is 44 45 pragma Compile_Time_Error 46 (Hash_Type'Modulus /= 2 ** 32 47 or else Hash_Type'First /= 0 48 or else Hash_Type'Last /= 2 ** 32 - 1, 49 "Hash_Type must be 32-bit modular with range 0 .. 2**32-1"); 50 51 function Shift_Left 52 (Value : Hash_Type; 53 Amount : Natural) return Hash_Type; 54 pragma Import (Intrinsic, Shift_Left); 55 56 H : Hash_Type; 57 58 begin 59 H := 0; 60 for J in Key'Range loop 61 H := Char_Type'Pos (Key (J)) 62 + Shift_Left (H, 6) + Shift_Left (H, 16) - H; 63 end loop; 64 65 return H; 66 end Hash; 67 68end System.String_Hash; 69