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                                  --
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   9 --                            $Revision: 1.10 $                             --
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  32 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
  33 --                                                                          --
  34 ------------------------------------------------------------------------------
  35
  36 with System.Unsigned_Types; use System.Unsigned_Types;
  37
  38 package body System.Exp_Uns is
  39
  40    ------------------
  41    -- Exp_Unsigned --
  42    ------------------
  43
  44    function Exp_Unsigned
  45      (Left  : Unsigned;
  46       Right : Natural)
  47       return  Unsigned
  48    is
  49       Result  : Unsigned := 1;
  50       Factor  : Unsigned := Left;
  51       Exp     : Natural := Right;
  52
  53    begin
  54       --  We use the standard logarithmic approach, Exp gets shifted right
  55       --  testing successive low order bits and Factor is the value of the
  56       --  base raised to the next power of 2.
  57
  58       --  Note: it is not worth special casing the cases of base values -1,0,+1
  59       --  since the expander does this when the base is a literal, and other
  60       --  cases will be extremely rare.
  61
  62       if Exp /= 0 then
  63          loop
  64             if Exp rem 2 /= 0 then
  65                Result := Result * Factor;
  66             end if;
  67
  68             Exp := Exp / 2;
  69             exit when Exp = 0;
  70             Factor := Factor * Factor;
  71          end loop;
  72       end if;
  73
  74       return Result;
  75    end Exp_Unsigned;
  76
  77 end System.Exp_Uns;