gcc/ada/libgnat/s-expuns.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --                       S Y S T E M . E X P _ U N S                        --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2018, 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
  32 with System.Unsigned_Types; use System.Unsigned_Types;
  33
  34 package body System.Exp_Uns is
  35
  36    ------------------
  37    -- Exp_Unsigned --
  38    ------------------
  39
  40    function Exp_Unsigned
  41      (Left  : Unsigned;
  42       Right : Natural)
  43       return  Unsigned
  44    is
  45       Result  : Unsigned := 1;
  46       Factor  : Unsigned := Left;
  47       Exp     : Natural := Right;
  48
  49    begin
  50       --  We use the standard logarithmic approach, Exp gets shifted right
  51       --  testing successive low order bits and Factor is the value of the
  52       --  base raised to the next power of 2.
  53
  54       --  Note: it is not worth special casing the cases of base values -1,0,+1
  55       --  since the expander does this when the base is a literal, and other
  56       --  cases will be extremely rare.
  57
  58       if Exp /= 0 then
  59          loop
  60             if Exp rem 2 /= 0 then
  61                Result := Result * Factor;
  62             end if;
  63
  64             Exp := Exp / 2;
  65             exit when Exp = 0;
  66             Factor := Factor * Factor;
  67          end loop;
  68       end if;
  69
  70       return Result;
  71    end Exp_Unsigned;
  72
  73 end System.Exp_Uns;