------------------------------------------------------------------------------ -- -- -- GNAT RUNTIME COMPONENTS -- -- -- -- S Y S T E M . E X N _ G E N -- -- -- -- B o d y -- -- -- -- -- -- 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.Exn_Gen is -------------------- -- Exn_Float_Type -- -------------------- function Exn_Float_Type (Left : Type_Of_Base; Right : Integer) return Type_Of_Base is pragma Suppress (Division_Check); pragma Suppress (Overflow_Check); pragma Suppress (Range_Check); 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 -- Division by this factor. if Exp >= 0 then loop if Exp rem 2 /= 0 then Result := Result * Factor; end if; Exp := Exp / 2; exit when Exp = 0; Factor := Factor * Factor; end loop; return Result; -- 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 raise Constraint_Error; -- Here we have a non-zero base and a negative exponent 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 essentially have is -- 1.0 / infinity, and the closest model number will be zero. begin loop if Exp rem 2 /= 0 then Result := Result * Factor; end if; Exp := Exp / 2; exit when Exp = 0; Factor := Factor * Factor; end loop; return 1.0 / Result; exception when Constraint_Error => return 0.0; end; end if; end Exn_Float_Type; ---------------------- -- Exn_Integer_Type -- ---------------------- -- 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; Right : Natural) return Type_Of_Base is pragma Suppress (Division_Check); pragma Suppress (Overflow_Check); 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 Result := Result * Factor; end if; Exp := Exp / 2; exit when Exp = 0; Factor := Factor * Factor; end loop; end if; return Result; end Exn_Integer_Type; end System.Exn_Gen;