1------------------------------------------------------------------------------ 2-- -- 3-- GNAT RUN-TIME COMPONENTS -- 4-- -- 5-- S Y S T E M . E X P O N T -- 6-- -- 7-- B o d y -- 8-- -- 9-- Copyright (C) 1992-2020, Free Software Foundation, Inc. -- 10-- -- 11-- GNAT is free software; you can redistribute it and/or modify it under -- 12-- terms of the GNU General Public License as published by the Free Soft- -- 13-- ware Foundation; either version 3, or (at your option) any later ver- -- 14-- sion. GNAT is distributed in the hope that it will be useful, but WITH- -- 15-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- 16-- or FITNESS FOR A PARTICULAR PURPOSE. -- 17-- -- 18-- As a special exception under Section 7 of GPL version 3, you are granted -- 19-- additional permissions described in the GCC Runtime Library Exception, -- 20-- version 3.1, as published by the Free Software Foundation. -- 21-- -- 22-- You should have received a copy of the GNU General Public License and -- 23-- a copy of the GCC Runtime Library Exception along with this program; -- 24-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see -- 25-- <http://www.gnu.org/licenses/>. -- 26-- -- 27-- GNAT was originally developed by the GNAT team at New York University. -- 28-- Extensive contributions were provided by Ada Core Technologies Inc. -- 29-- -- 30------------------------------------------------------------------------------ 31 32function System.Expont (Left : Int; Right : Natural) return Int is 33 34 -- Note that negative exponents get a constraint error because the 35 -- subtype of the Right argument (the exponent) is Natural. 36 37 Result : Int := 1; 38 Factor : Int := Left; 39 Exp : Natural := Right; 40 41begin 42 -- We use the standard logarithmic approach, Exp gets shifted right 43 -- testing successive low order bits and Factor is the value of the 44 -- base raised to the next power of 2. 45 46 -- Note: it is not worth special casing base values -1, 0, +1 since 47 -- the expander does this when the base is a literal, and other cases 48 -- will be extremely rare. 49 50 if Exp /= 0 then 51 loop 52 if Exp rem 2 /= 0 then 53 declare 54 pragma Unsuppress (Overflow_Check); 55 begin 56 Result := Result * Factor; 57 end; 58 end if; 59 60 Exp := Exp / 2; 61 exit when Exp = 0; 62 63 declare 64 pragma Unsuppress (Overflow_Check); 65 begin 66 Factor := Factor * Factor; 67 end; 68 end loop; 69 end if; 70 71 return Result; 72end System.Expont; 73