155 lines
5.9 KiB
Ada
155 lines
5.9 KiB
Ada
------------------------------------------------------------------------------
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-- --
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-- GNAT RUNTIME COMPONENTS --
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-- --
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-- S Y S T E M . E X N _ G E N --
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-- --
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-- B o d y --
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-- --
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-- $Revision: 1.9 $
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-- --
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-- Copyright (C) 1992-2001, 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 2, 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. See the GNU General Public License --
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-- for more details. You should have received a copy of the GNU General --
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-- Public License distributed with GNAT; see file COPYING. If not, write --
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-- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
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-- MA 02111-1307, USA. --
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-- --
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-- As a special exception, if other files instantiate generics from this --
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-- unit, or you link this unit with other files to produce an executable, --
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-- this unit does not by itself cause the resulting executable to be --
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-- covered by the GNU General Public License. This exception does not --
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-- however invalidate any other reasons why the executable file might be --
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-- covered by the GNU Public License. --
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-- --
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-- GNAT was originally developed by the GNAT team at New York University. --
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-- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
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-- --
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------------------------------------------------------------------------------
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package body System.Exn_Gen is
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--------------------
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-- Exn_Float_Type --
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--------------------
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function Exn_Float_Type
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(Left : Type_Of_Base;
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Right : Integer)
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return Type_Of_Base
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is
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pragma Suppress (Division_Check);
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pragma Suppress (Overflow_Check);
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pragma Suppress (Range_Check);
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Result : Type_Of_Base := 1.0;
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Factor : Type_Of_Base := Left;
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Exp : Integer := Right;
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begin
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-- We use the standard logarithmic approach, Exp gets shifted right
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-- testing successive low order bits and Factor is the value of the
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-- base raised to the next power of 2. For positive exponents we
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-- multiply the result by this factor, for negative exponents, we
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-- Division by this factor.
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if Exp >= 0 then
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loop
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if Exp rem 2 /= 0 then
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Result := Result * Factor;
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end if;
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Exp := Exp / 2;
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exit when Exp = 0;
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Factor := Factor * Factor;
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end loop;
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return Result;
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-- Negative exponent. For a zero base, we should arguably return an
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-- infinity of the right sign, but it is not clear that there is
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-- proper authorization to do so, so for now raise Constraint_Error???
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elsif Factor = 0.0 then
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raise Constraint_Error;
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-- Here we have a non-zero base and a negative exponent
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else
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-- For the negative exponent case, a constraint error during this
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-- calculation happens if Factor gets too large, and the proper
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-- response is to return 0.0, since what we essentially have is
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-- 1.0 / infinity, and the closest model number will be zero.
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begin
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loop
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if Exp rem 2 /= 0 then
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Result := Result * Factor;
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end if;
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Exp := Exp / 2;
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exit when Exp = 0;
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Factor := Factor * Factor;
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end loop;
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return 1.0 / Result;
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exception
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when Constraint_Error =>
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return 0.0;
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end;
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end if;
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end Exn_Float_Type;
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----------------------
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-- Exn_Integer_Type --
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----------------------
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-- Note that negative exponents get a constraint error because the
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-- subtype of the Right argument (the exponent) is Natural.
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function Exn_Integer_Type
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(Left : Type_Of_Base;
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Right : Natural)
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return Type_Of_Base
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is
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pragma Suppress (Division_Check);
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pragma Suppress (Overflow_Check);
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Result : Type_Of_Base := 1;
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Factor : Type_Of_Base := Left;
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Exp : Natural := Right;
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begin
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-- We use the standard logarithmic approach, Exp gets shifted right
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-- testing successive low order bits and Factor is the value of the
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-- base raised to the next power of 2.
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-- Note: it is not worth special casing the cases of base values -1,0,+1
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-- since the expander does this when the base is a literal, and other
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-- cases will be extremely rare.
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if Exp /= 0 then
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loop
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if Exp rem 2 /= 0 then
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Result := Result * Factor;
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end if;
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Exp := Exp / 2;
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exit when Exp = 0;
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Factor := Factor * Factor;
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end loop;
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end if;
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return Result;
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end Exn_Integer_Type;
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end System.Exn_Gen;
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