+++ /dev/null
-------------------------------------------------------------------------------
--- --
--- GNAT RUNTIME COMPONENTS --
--- --
--- S Y S T E M . E X P _ G E N --
--- --
--- B o d y --
--- --
--- $Revision: 1.1.16.1 $
--- --
--- 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- --
--- 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 --
--- 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 --
--- 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. --
--- --
--- GNAT was originally developed by the GNAT team at New York University. --
--- Extensive contributions were provided by Ada Core Technologies Inc. --
--- --
-------------------------------------------------------------------------------
-
-package body System.Exp_Gen is
-
- --------------------
- -- Exp_Float_Type --
- --------------------
-
- function Exp_Float_Type
- (Left : Type_Of_Base;
- Right : Integer)
- return Type_Of_Base
- is
- Result : Type_Of_Base := 1.0;
- Factor : Type_Of_Base := Left;
- Exp : Integer := Right;
-
- 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
- -- divide by this factor.
-
- if Exp >= 0 then
-
- -- For a positive exponent, if we get a constraint error during
- -- this loop, it is an overflow, and the constraint error will
- -- simply be passed on to the caller.
-
- loop
- if Exp rem 2 /= 0 then
- declare
- pragma Unsuppress (All_Checks);
- begin
- Result := Result * Factor;
- end;
- end if;
-
- Exp := Exp / 2;
- exit when Exp = 0;
-
- declare
- pragma Unsuppress (All_Checks);
- begin
- Factor := Factor * Factor;
- end;
- end loop;
-
- return Result;
-
- -- Now we know that the exponent is negative, check for case of
- -- base of 0.0 which always generates a constraint error.
-
- elsif Factor = 0.0 then
- raise Constraint_Error;
-
- -- Here we have a negative exponent with a non-zero base
-
- else
-
- -- 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 essenmtially have is
- -- 1.0 / infinity, and the closest model number will be zero.
-
- begin
- loop
- if Exp rem 2 /= 0 then
- declare
- pragma Unsuppress (All_Checks);
- begin
- Result := Result * Factor;
- end;
- end if;
-
- Exp := Exp / 2;
- exit when Exp = 0;
-
- declare
- pragma Unsuppress (All_Checks);
- begin
- Factor := Factor * Factor;
- end;
- end loop;
-
- declare
- pragma Unsuppress (All_Checks);
- begin
- return 1.0 / Result;
- end;
-
- exception
-
- when Constraint_Error =>
- return 0.0;
- end;
- end if;
- end Exp_Float_Type;
-
- ----------------------
- -- Exp_Integer_Type --
- ----------------------
-
- -- Note that negative exponents get a constraint error because the
- -- subtype of the Right argument (the exponent) is Natural.
-
- function Exp_Integer_Type
- (Left : Type_Of_Base;
- Right : Natural)
- return Type_Of_Base
- is
- Result : Type_Of_Base := 1;
- Factor : Type_Of_Base := Left;
- Exp : Natural := Right;
-
- 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.
-
- -- 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
- loop
- if Exp rem 2 /= 0 then
- declare
- pragma Unsuppress (All_Checks);
- begin
- Result := Result * Factor;
- end;
- end if;
-
- Exp := Exp / 2;
- exit when Exp = 0;
-
- declare
- pragma Unsuppress (All_Checks);
- begin
- Factor := Factor * Factor;
- end;
- end loop;
- end if;
-
- return Result;
- end Exp_Integer_Type;
-
-end System.Exp_Gen;
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