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