| ------------------------------------------------------------------------------ |
| -- -- |
| -- 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) 2009-2021, 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 follows the algorithm |
| -- introduced in the ndbm substitute SDBM by Ozan Yigit and then reused in |
| -- GNU Awk (where they are implemented as a Duff's device). |
| |
| ---------- |
| -- 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; |
