------------------------------------------------------------------------------
--                                                                          --
--                         GNAT COMPILER COMPONENTS                         --
--                                                                          --
--                       S Y S T E M . V A L _ U N S                        --
--                                                                          --
--                                 B o d y                                  --
--                                                                          --
--                            $Revision: 1.6 $                              --
--                                                                          --
--           Copyright (c) 1992,1993,1994 NYU, All Rights Reserved          --
--                                                                          --
-- The GNAT library is free software; you can redistribute it and/or modify --
-- it under terms of the GNU Library General Public License as published by --
-- the Free Software  Foundation; either version 2, or (at your option) any --
-- later version.  The GNAT library is distributed in the hope that it will --
-- be useful, but WITHOUT ANY WARRANTY;  without even  the implied warranty --
-- of MERCHANTABILITY  or  FITNESS FOR  A PARTICULAR PURPOSE.  See the  GNU --
-- Library  General  Public  License for  more  details.  You  should  have --
-- received  a copy of the GNU  Library  General Public License  along with --
-- the GNAT library;  see the file  COPYING.LIB.  If not, write to the Free --
-- Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.        --
--                                                                          --
------------------------------------------------------------------------------

with System.Unsigned_Types; use System.Unsigned_Types;
with System.Val_Util;       use System.Val_Util;

package body System.Val_Uns is

   -------------------
   -- Scan_Unsigned --
   -------------------

   function Scan_Unsigned
     (Str  : String;
      Ptr  : access Positive'Base;
      Max  : Positive'Base)
      return Unsigned
   is
      P : Positive'Base;
      --  Local copy of the pointer

      Uval : Unsigned;
      --  Accumulated unsigned integer result (in the loop to scan out based
      --  numbers, this is the value of the base, scanned on entry)

      Bval : Unsigned;
      --  Value of based number accumulated

      New_Val : Unsigned;
      --  Used in checking overflow during accumulation of result

      Expon : Integer;
      --  Exponent value

      Minus : Boolean := False;
      --  Set to True if minus sign is present, otherwise to False. Note that
      --  a minus sign is permissible for the singular case of -0, and in any
      --  case the pointer is left pointing past a negative integer literal.

      Overflow : Boolean := False;
      --  Set True if overflow is detected at any point

      Start : Positive;
      --  Save location of first non-blank character

      Base_Char : Character;
      --  Base character (# or :) in based case

      Base : Unsigned := 10;
      --  Base value (reset in based case)

      Digit : Unsigned;
      --  Digit value (0..15) in based case

   begin
      Scan_Sign (Str, Ptr, Max, Minus, Start);

      if Str (Ptr.all) not in '0' .. '9' then
         Ptr.all := Start;
         raise Constraint_Error;
      end if;

      P := Ptr.all;
      Uval := Character'Pos (Str (P)) - Character'Pos ('0');

      --  Loop to scan out digits of what is either the number or the base

      loop
         P := P + 1;
         exit when P > Max;

         --  Non-digit encountered

         if Str (P) not in '0' .. '9' then

            --  Only possibility is syntactically valid underline which we skip
            --  otherwise exit from the loop, we are done with the scan.

            exit when Str (P) /= '_'
              or else P >= Max
              or else Str (P + 1) not in '0' .. '9';

         --  Accumulate result unless we have overflow. Overflow is detected
         --  by the wrap around, which results in the a smaller value.

         else
            New_Val :=
              10 * Uval + Character'Pos (Str (P)) - Character'Pos ('0');

            if New_Val < Uval then
               Overflow := True;
            else
               Uval := New_Val;
            end if;
         end if;
      end loop;

      Ptr.all := P;

      --  Deal with based case

      if P < Max and then (Str (P) = ':' or else Str (P) = '#') then
         Base_Char := Str (P);
         P := P + 1;
         Bval := 0;

         --  Check base value. Overflow is set True if we find a bad base, or
         --  a digit that is out of range of the base. That way, we scan out
         --  the numeral that is still syntactically correct, though illegal.

         if Uval not in 2 .. 16 then
            Overflow := True;
         end if;

         --  Loop to scan out based integer value

         loop
            --  We require a digit at this stage. If we don't have one, then
            --  it isn't a based number after all, so the number we scanned
            --  out as the base (still in Uval) is the value we wnat.

            if Str (P) in '0' .. '9' then
               Digit := Character'Pos (Str (P)) - Character'Pos ('0');

            elsif Str (P) in 'A' .. 'F' then
               Digit := Character'Pos (Str (P)) - (Character'Pos ('A') - 10);

            elsif Str (P) in 'a' .. 'f' then
               Digit := Character'Pos (Str (P)) - (Character'Pos ('a') - 10);
            else
               exit;
            end if;

            --  Here we accumulate the value, checking overflow (which
            --  is detected by wrap around leaving the result smaller)

            if Digit >= Uval then
               Overflow := True;
            else
               New_Val := Bval * Uval + Digit;

               if New_Val < Bval then
                  Overflow := True;
               else
                  Bval := New_Val;
               end if;
            end if;

            --  If at end of string with no base char, not a based number

            P := P + 1;
            exit when P > Max;

            --  If terminating base character, we are done with loop

            if Str (P) = Base_Char then
               Ptr.all := P + 1;
               Base := Uval;
               Uval := Bval;
               exit;

            --  Just ignore an underline. Note that we will end up requiring a
            --  digit to follow the underline, thus rejecting double underline

            elsif Str (P) = '_' then
               P := P + 1;
               exit when P > Max;
            end if;

         end loop;
      end if;

      --  Come here with scanned unsigned value in Uval. The only remaining
      --  required step is to deal with exponent if one is present.

      Expon := Scan_Exponent (Str, Ptr, Max);

      if Expon /= 0 and then Uval /= 0 then

         --  For non-zero value, scale by exponent value. No need to do this
         --  efficiently, since use of exponent in integer literals is rare,
         --  and in any case the exponent cannot be very large.

         loop
            New_Val := Uval * Base;

            if New_Val < Uval then
               Overflow := True;
            else
               Uval := New_Val;
            end if;

            Expon := Expon - 1;
            exit when Expon = 0;
         end loop;
      end if;

      --  Return result, dealing with sign and overflow

      if Overflow or else (Minus and then Uval /= 0) then
         raise Constraint_Error;
      else
         return Uval;
      end if;

   end Scan_Unsigned;

   --------------------
   -- Value_Unsigned --
   --------------------

   function Value_Unsigned (Str : String) return Unsigned is
      V : Unsigned;
      P : aliased Natural := Str'First;

   begin
      V := Scan_Unsigned (Str, P'Access, Str'Last);
      Scan_Trailing_Blanks (Str, P);
      return V;

   end Value_Unsigned;

end System.Val_Uns;
