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File : s-valuns.adb


------------------------------------------------------------------------------
--                                                                          --
--                         GNAT COMPILER COMPONENTS                         --
--                                                                          --
--                       S Y S T E M . V A L _ U N S                        --
--                                                                          --
--                                 B o d y                                  --
--                                                                          --
--                            $Revision: 1.13 $                             --
--                                                                          --
--          Copyright (C) 1992-1997 Free Software Foundation, Inc.          --
--                                                                          --
-- GNAT is free software;  you can  redistribute it  and/or modify it under --
-- terms of the  GNU General Public License as published  by the Free Soft- --
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-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
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-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
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-- MA 02111-1307, USA.                                                      --
--                                                                          --
-- As a special exception,  if other files  instantiate  generics from this --
-- unit, or you link  this unit with other files  to produce an executable, --
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-- covered  by the  GNU  General  Public  License.  This exception does not --
-- however invalidate  any other reasons why  the executable file  might be --
-- covered by the  GNU Public License.                                      --
--                                                                          --
-- GNAT was originally developed  by the GNAT team at  New York University. --
-- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
--                                                                          --
------------------------------------------------------------------------------

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 Integer;
      Max  : Integer)
      return Unsigned
   is
      P : Integer;
      --  Local copy of the pointer

      Uval : Unsigned;
      --  Accumulated unsigned integer 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

   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');
      P := P + 1;

      --  Scan out digits of what is either the number or the base.
      --  In either case, we are definitely scanning out in base 10.

      declare
         Umax : constant := (Unsigned'Last - 9) / 10;
         --  Max value which cannot overflow on accumulating next digit

         Umax10 : constant := Unsigned'Last / 10;
         --  Numbers bigger than Umax10 overflow if multiplied by 10

      begin
         --  Loop through decimal digits
         loop
            exit when P > Max;

            Digit := Character'Pos (Str (P)) - Character'Pos ('0');

            --  Non-digit encountered

            if Digit > 9 then
               if Str (P) = '_' then
                  Scan_Underscore (Str, P, Ptr, Max, False);
               else
                  exit;
               end if;

            --  Accumulate result, checking for overflow

            else
               if Uval <= Umax then
                  Uval := 10 * Uval + Digit;

               elsif Uval > Umax10 then
                  Overflow := True;

               else
                  Uval := 10 * Uval + Digit;

                  if Uval < Umax10 then
                     Overflow := True;
                  end if;
               end if;

               P := P + 1;
            end if;
         end loop;
      end;

      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;
         Base := Uval;
         Uval := 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.
         --  We use a safe base of 16 for this scan, to avoid zero divide.

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

         --  Scan out based integer

         declare
            Umax : constant Unsigned := (Unsigned'Last - Base + 1) / Base;
            --  Max value which cannot overflow on accumulating next digit

            UmaxB : constant Unsigned := Unsigned'Last / Base;
            --  Numbers bigger than UmaxB overflow if multiplied by base

         begin
            --  Loop to scan out based integer value

            loop
               --  We require a digit at this stage

               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);

               --  If we don't have a digit, then this is not a based number
               --  after all, so we use the value we scanned out as the base
               --  (now in Base), and the pointer to the base character was
               --  already stored in Ptr.all.

               else
                  Uval := Base;
                  exit;
               end if;

               --  If digit is too large, just signal overflow and continue.
               --  The idea here is to keep scanning as long as the input is
               --  syntactically valid, even if we have detected overflow

               if Digit >= Base then
                  Overflow := True;

               --  Here we accumulate the value, checking overflow

               elsif Uval <= Umax then
                  Uval := Base * Uval + Digit;

               elsif Uval > UmaxB then
                  Overflow := True;

               else
                  Uval := Base * Uval + Digit;

                  if Uval < UmaxB then
                     Overflow := True;
                  end if;
               end if;

               --  If at end of string with no base char, not a based number
               --  but we signal Constraint_Error and set the pointer past
               --  the end of the field, since this is what the ACVC tests
               --  seem to require, see CE3704N, line 204.

               P := P + 1;

               if P > Max then
                  Ptr.all := P;
                  raise Constraint_Error;
               end if;

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

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

               --  Deal with underscore

               elsif Str (P) = '_' then
                  Scan_Underscore (Str, P, Ptr, Max, True);
               end if;

            end loop;
         end;
      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.

         declare
            UmaxB : constant Unsigned := Unsigned'Last / Base;
            --  Numbers bigger than UmaxB overflow if multiplied by base

         begin
            for J in 1 .. Expon loop
               if Uval > UmaxB then
                  Overflow := True;
                  exit;
               end if;

               Uval := Uval * Base;
            end loop;
         end;
      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 Integer := 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;