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Diffstat (limited to 'gcc/ada/libgnat/s-expont.adb')
-rw-r--r-- | gcc/ada/libgnat/s-expont.adb | 72 |
1 files changed, 72 insertions, 0 deletions
diff --git a/gcc/ada/libgnat/s-expont.adb b/gcc/ada/libgnat/s-expont.adb new file mode 100644 index 0000000..bcdcae4 --- /dev/null +++ b/gcc/ada/libgnat/s-expont.adb @@ -0,0 +1,72 @@ +------------------------------------------------------------------------------ +-- -- +-- GNAT RUN-TIME COMPONENTS -- +-- -- +-- S Y S T E M . E X P O N T -- +-- -- +-- B o d y -- +-- -- +-- Copyright (C) 1992-2020, 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 3, 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. -- +-- -- +-- As a special exception under Section 7 of GPL version 3, you are granted -- +-- additional permissions described in the GCC Runtime Library Exception, -- +-- version 3.1, as published by the Free Software Foundation. -- +-- -- +-- You should have received a copy of the GNU General Public License and -- +-- a copy of the GCC Runtime Library Exception along with this program; -- +-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see -- +-- <http://www.gnu.org/licenses/>. -- +-- -- +-- GNAT was originally developed by the GNAT team at New York University. -- +-- Extensive contributions were provided by Ada Core Technologies Inc. -- +-- -- +------------------------------------------------------------------------------ + +function System.Expont (Left : Int; Right : Natural) return Int is + + -- Note that negative exponents get a constraint error because the + -- subtype of the Right argument (the exponent) is Natural. + + Result : Int := 1; + Factor : Int := 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 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 (Overflow_Check); + begin + Result := Result * Factor; + end; + end if; + + Exp := Exp / 2; + exit when Exp = 0; + + declare + pragma Unsuppress (Overflow_Check); + begin + Factor := Factor * Factor; + end; + end loop; + end if; + + return Result; +end System.Expont; |