File : s-exngen.adb
------------------------------------------------------------------------------
-- --
-- GNAT RUNTIME COMPONENTS --
-- --
5 -- S Y S T E M . E X N _ G E N --
-- --
-- B o d y --
-- --
-- $Revision: 1.9 $
10 -- --
-- Copyright (C) 1992-2001, 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- --
15 -- ware Foundation; either version 2, 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. See the GNU General Public License --
-- for more details. You should have received a copy of the GNU General --
20 -- Public License distributed with GNAT; see file COPYING. If not, write --
-- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
-- MA 02111-1307, USA. --
-- --
-- As a special exception, if other files instantiate generics from this --
25 -- unit, or you link this unit with other files to produce an executable, --
-- this unit does not by itself cause the resulting executable to be --
-- covered by the GNU General Public License. This exception does not --
-- however invalidate any other reasons why the executable file might be --
-- covered by the GNU Public License. --
30 -- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
-- --
------------------------------------------------------------------------------
35
package body System.Exn_Gen is
--------------------
-- Exn_Float_Type --
40 --------------------
function Exn_Float_Type
(Left : Type_Of_Base;
Right : Integer)
45 return Type_Of_Base
is
pragma Suppress (Division_Check);
pragma Suppress (Overflow_Check);
pragma Suppress (Range_Check);
50
Result : Type_Of_Base := 1.0;
Factor : Type_Of_Base := Left;
Exp : Integer := Right;
55 begin
-- We use the standard logarithmic approach, Exp gets shifted right
-- testing successive low order bits and Factor is the value of the
-- base raised to the next power of 2. For positive exponents we
-- multiply the result by this factor, for negative exponents, we
60 -- Division by this factor.
if Exp >= 0 then
loop
if Exp rem 2 /= 0 then
65 Result := Result * Factor;
end if;
Exp := Exp / 2;
exit when Exp = 0;
70 Factor := Factor * Factor;
end loop;
return Result;
75 -- Negative exponent. For a zero base, we should arguably return an
-- infinity of the right sign, but it is not clear that there is
-- proper authorization to do so, so for now raise Constraint_Error???
elsif Factor = 0.0 then
80 raise Constraint_Error;
-- Here we have a non-zero base and a negative exponent
else
85 -- For the negative exponent case, a constraint error during this
-- calculation happens if Factor gets too large, and the proper
-- response is to return 0.0, since what we essentially have is
-- 1.0 / infinity, and the closest model number will be zero.
90 begin
loop
if Exp rem 2 /= 0 then
Result := Result * Factor;
end if;
95
Exp := Exp / 2;
exit when Exp = 0;
Factor := Factor * Factor;
end loop;
100
return 1.0 / Result;
exception
105 when Constraint_Error =>
return 0.0;
end;
end if;
end Exn_Float_Type;
110
----------------------
-- Exn_Integer_Type --
----------------------
115 -- Note that negative exponents get a constraint error because the
-- subtype of the Right argument (the exponent) is Natural.
function Exn_Integer_Type
(Left : Type_Of_Base;
120 Right : Natural)
return Type_Of_Base
is
pragma Suppress (Division_Check);
pragma Suppress (Overflow_Check);
125
Result : Type_Of_Base := 1;
Factor : Type_Of_Base := Left;
Exp : Natural := Right;
130 begin
-- We use the standard logarithmic approach, Exp gets shifted right
-- testing successive low order bits and Factor is the value of the
-- base raised to the next power of 2.
135 -- Note: it is not worth special casing the cases of base values -1,0,+1
-- since the expander does this when the base is a literal, and other
-- cases will be extremely rare.
if Exp /= 0 then
140 loop
if Exp rem 2 /= 0 then
Result := Result * Factor;
end if;
145 Exp := Exp / 2;
exit when Exp = 0;
Factor := Factor * Factor;
end loop;
end if;
150
return Result;
end Exn_Integer_Type;
end System.Exn_Gen;