gcc/ada/s-expuns.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUNTIME 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) 1992-1997 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- --
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  20 -- MA 02111-1307, USA.                                                      --
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  22 -- As a special exception,  if other files  instantiate  generics from this --
  23 -- unit, or you link  this unit with other files  to produce an executable, --
  24 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  25 -- covered  by the  GNU  General  Public  License.  This exception does not --
  26 -- however invalidate  any other reasons why  the executable file  might be --
  27 -- covered by the  GNU Public License.                                      --
  28 --                                                                          --
  29 -- GNAT was originally developed  by the GNAT team at  New York University. --
  30 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  31 --                                                                          --
  32 ------------------------------------------------------------------------------
  33
  34 with System.Unsigned_Types; use System.Unsigned_Types;
  35
  36 package body System.Exp_Uns is
  37
  38    ------------------
  39    -- Exp_Unsigned --
  40    ------------------
  41
  42    function Exp_Unsigned
  43      (Left  : Unsigned;
  44       Right : Natural)
  45       return  Unsigned
  46    is
  47       Result  : Unsigned := 1;
  48       Factor  : Unsigned := Left;
  49       Exp     : Natural := Right;
  50
  51    begin
  52       --  We use the standard logarithmic approach, Exp gets shifted right
  53       --  testing successive low order bits and Factor is the value of the
  54       --  base raised to the next power of 2.
  55
  56       --  Note: it is not worth special casing the cases of base values -1,0,+1
  57       --  since the expander does this when the base is a literal, and other
  58       --  cases will be extremely rare.
  59
  60       if Exp /= 0 then
  61          loop
  62             if Exp rem 2 /= 0 then
  63                Result := Result * Factor;
  64             end if;
  65
  66             Exp := Exp / 2;
  67             exit when Exp = 0;
  68             Factor := Factor * Factor;
  69          end loop;
  70       end if;
  71
  72       return Result;
  73    end Exp_Unsigned;
  74
  75 end System.Exp_Uns;