69 lines
3.2 KiB
Ada
69 lines
3.2 KiB
Ada
------------------------------------------------------------------------------
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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) 2009-2013, 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_Warning;
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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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