gcc/ada/s-exngen.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUNTIME COMPONENTS                          --
   4 --                                                                          --
   5 --                       S Y S T E M . E X N _ G E N                        --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --                            $Revision: 1.9 $
  10 --                                                                          --
  11 --          Copyright (C) 1992-2001, Free Software Foundation, Inc.         --
  12 --                                                                          --
  13 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  14 -- terms of the  GNU General Public License as published  by the Free Soft- --
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  17 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  18 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  19 -- for  more details.  You should have  received  a copy of the GNU General --
  20 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  21 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  22 -- MA 02111-1307, USA.                                                      --
  23 --                                                                          --
  24 -- As a special exception,  if other files  instantiate  generics from this --
  25 -- unit, or you link  this unit with other files  to produce an executable, --
  26 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  27 -- covered  by the  GNU  General  Public  License.  This exception does not --
  28 -- however invalidate  any other reasons why  the executable file  might be --
  29 -- covered by the  GNU Public License.                                      --
  30 --                                                                          --
  31 -- GNAT was originally developed  by the GNAT team at  New York University. --
  32 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
  33 --                                                                          --
  34 ------------------------------------------------------------------------------
  35
  36 package body System.Exn_Gen is
  37
  38    --------------------
  39    -- Exn_Float_Type --
  40    --------------------
  41
  42    function Exn_Float_Type
  43      (Left  : Type_Of_Base;
  44       Right : Integer)
  45       return  Type_Of_Base
  46    is
  47       pragma Suppress (Division_Check);
  48       pragma Suppress (Overflow_Check);
  49       pragma Suppress (Range_Check);
  50
  51       Result : Type_Of_Base := 1.0;
  52       Factor : Type_Of_Base := Left;
  53       Exp    : Integer := Right;
  54
  55    begin
  56       --  We use the standard logarithmic approach, Exp gets shifted right
  57       --  testing successive low order bits and Factor is the value of the
  58       --  base raised to the next power of 2. For positive exponents we
  59       --  multiply the result by this factor, for negative exponents, we
  60       --  Division by this factor.
  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
  73          return Result;
  74
  75       --  Negative exponent. For a zero base, we should arguably return an
  76       --  infinity of the right sign, but it is not clear that there is
  77       --  proper authorization to do so, so for now raise Constraint_Error???
  78
  79       elsif Factor = 0.0 then
  80          raise Constraint_Error;
  81
  82       --  Here we have a non-zero base and a negative exponent
  83
  84       else
  85          --  For the negative exponent case, a constraint error during this
  86          --  calculation happens if Factor gets too large, and the proper
  87          --  response is to return 0.0, since what we essentially have is
  88          --  1.0 / infinity, and the closest model number will be zero.
  89
  90          begin
  91             loop
  92                if Exp rem 2 /= 0 then
  93                   Result := Result * Factor;
  94                end if;
  95
  96                Exp := Exp / 2;
  97                exit when Exp = 0;
  98                Factor := Factor * Factor;
  99             end loop;
 100
 101             return 1.0 / Result;
 102
 103          exception
 104
 105             when Constraint_Error =>
 106                return 0.0;
 107          end;
 108       end if;
 109    end Exn_Float_Type;
 110
 111    ----------------------
 112    -- Exn_Integer_Type --
 113    ----------------------
 114
 115    --  Note that negative exponents get a constraint error because the
 116    --  subtype of the Right argument (the exponent) is Natural.
 117
 118    function Exn_Integer_Type
 119      (Left  : Type_Of_Base;
 120       Right : Natural)
 121       return  Type_Of_Base
 122    is
 123       pragma Suppress (Division_Check);
 124       pragma Suppress (Overflow_Check);
 125
 126       Result : Type_Of_Base := 1;
 127       Factor : Type_Of_Base := Left;
 128       Exp    : Natural := Right;
 129
 130    begin
 131       --  We use the standard logarithmic approach, Exp gets shifted right
 132       --  testing successive low order bits and Factor is the value of the
 133       --  base raised to the next power of 2.
 134
 135       --  Note: it is not worth special casing the cases of base values -1,0,+1
 136       --  since the expander does this when the base is a literal, and other
 137       --  cases will be extremely rare.
 138
 139       if Exp /= 0 then
 140          loop
 141             if Exp rem 2 /= 0 then
 142                Result := Result * Factor;
 143             end if;
 144
 145             Exp := Exp / 2;
 146             exit when Exp = 0;
 147             Factor := Factor * Factor;
 148          end loop;
 149       end if;
 150
 151       return Result;
 152    end Exn_Integer_Type;
 153
 154 end System.Exn_Gen;