gcc/ada/s-expllu.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUNTIME COMPONENTS                          --
   4 --                                                                          --
   5 --                        S Y S T E M . X P _ B M L                         --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --                                                                          --
  10 --        Copyright (C) 1992,1993,1994 Free Software Foundation, Inc.       --
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  13 -- terms of the  GNU General Public License as published  by the Free Soft- --
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  23 -- As a special exception,  if other files  instantiate  generics from this --
  24 -- unit, or you link  this unit with other files  to produce an executable, --
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  26 -- covered  by the  GNU  General  Public  License.  This exception does not --
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  28 -- covered by the  GNU Public License.                                      --
  29 --                                                                          --
  30 -- GNAT was originally developed  by the GNAT team at  New York University. --
  31 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
  32 --                                                                          --
  33 ------------------------------------------------------------------------------
  34
  35 with System.Unsigned_Types; use System.Unsigned_Types;
  36
  37 package body System.Exp_LLU is
  38
  39    ----------------------------
  40    -- Exp_Long_Long_Unsigned --
  41    ----------------------------
  42
  43    function Exp_Long_Long_Unsigned
  44      (Left  : Long_Long_Unsigned;
  45       Right : Natural)
  46       return  Long_Long_Unsigned
  47    is
  48       Result : Long_Long_Unsigned := 1;
  49       Factor : Long_Long_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
  75    end Exp_Long_Long_Unsigned;
  76
  77 end System.Exp_LLU;