------------------------------------------------------------------------------
--                                                                          --
--                         GNAT COMPILER COMPONENTS                         --
--                                                                          --
--            I N T E R F A C E S . P A C K E D _ D E C I M A L             --
--                                                                          --
--                                 S p e c                                  --
--            (Version for IBM Mainframe Packed Decimal Format)             --
--                                                                          --
--                            $Revision: 1.1 $                              --
--                                                                          --
-- 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.        --
--                                                                          --
------------------------------------------------------------------------------

--  This unit defines the packed decimal format used by GNAT in response to
--  a specication of Machine_Radix 10 for a decimal fixed-point type. The
--  format and operations are completely encapsulated in this unit, so all
--  that is necessary to compile using different packed decimal formats is
--  to replace this single unit.

--  Note that the compiler access the spec of this unit during compilation
--  to obtain the data length that needs allocating, so the correct version
--  of the spec must be available to the compiler, and must correspond to
--  the spec and body made available to the linker, and all units of a given
--  program must be compiled with the same version of the spec and body.
--  This consistency will be enforced automatically using the normal binder
--  consistency checking, since any unit declaring Machine_Radix 10 types or
--  containing operations on such data will implicitly with Packed_Decimal.

with System;

package Interfaces.Packed_Decimal is

   ------------------------
   -- Format Description --
   ------------------------

   --  IBM Mainframe packed decimal format uses a byte string of length one
   --  to 10 bytes, with the most significant byte first. Each byte contains
   --  two decimal digits (with the high order digit in the left nibble, and
   --  the low order four bits contain the sign, using the following code:

   --     16#A#  2#1010#   positive
   --     16#B#  2#1011#   negative
   --     16#C#  2#1100#   positive (preferred representation)
   --     16#D#  2#1101#   negative (preferred representation)
   --     16#E#  2#1110#   positive
   --     16#F#  2#1011#   positive

   --  In this package, all six sign representations are interpreted as
   --  shown above when an operand is read, when an operand is written,
   --  the preferred representations are always used. Constraint_Error
   --  is raised if any other bit pattern is found in the sign nibble,
   --  or if a digit nibble contains an invalid digit code.

   --  Some examples follow:

   --     05 76 3C      +5763
   --     00 01 1D        -11
   --     00 04 4E        +44 (non-standard sign)
   --     00 00 00      invalid (incorrect sign nibble)
   --     0A 01 1C      invalid (bad digit)

   ------------------
   -- Length Array --
   ------------------

   --  The following array must be declared in exactly the form shown, since
   --  the compiler accesses the associated tree to determine the size to be
   --  allocated to a machine radix 10 type, depending on the number of digits.

   subtype Byte_Length is Positive range 1 .. 10;
   --  Range of possible byte lengths

   Packed_Size : constant array (1 .. 18) of Byte_Length :=
      (01 => 01,    -- Length in bytes for digits 1
       02 => 02,    -- Length in bytes for digits 2
       03 => 02,    -- Length in bytes for digits 2
       04 => 03,    -- Length in bytes for digits 2
       05 => 03,    -- Length in bytes for digits 2
       06 => 04,    -- Length in bytes for digits 2
       07 => 04,    -- Length in bytes for digits 2
       08 => 05,    -- Length in bytes for digits 2
       09 => 05,    -- Length in bytes for digits 2
       10 => 06,    -- Length in bytes for digits 2
       11 => 06,    -- Length in bytes for digits 2
       12 => 07,    -- Length in bytes for digits 2
       13 => 07,    -- Length in bytes for digits 2
       14 => 08,    -- Length in bytes for digits 2
       15 => 08,    -- Length in bytes for digits 2
       16 => 09,    -- Length in bytes for digits 2
       17 => 09,    -- Length in bytes for digits 2
       18 => 10);   -- Length in bytes for digits 2

   -------------------------
   -- Conversion Routines --
   -------------------------

   subtype D32 is Positive range 1 .. 9;
   --  Used to represent number of digits in a packed decimal value that
   --  can be represented in a 32-bit binary signed integer form.

   subtype D64 is Positive range 10 .. 18;
   --  Used to represent number of digits in a packed decimal value that
   --  requires a 64-bit signed binary integer for representing all values.

   function Packed_To_Int32 (P : System.Address; D : D32) return Integer_32;
   --  The argument P is the address of a packed decimal value and D is the
   --  number of digits (in the range 1 .. 9, as implied by the subtype).
   --  The returned result is the corresponding signed binary value. The
   --  exception Constraint_Error is raised if the input is invalid.

   function Packed_To_Int64 (P : System.Address; D : D64) return Integer_64;
   --  The argument P is the address of a packed decimal value and D is the
   --  number of digits (in the range 10 .. 18, as implied by the subtype).
   --  The returned result is the corresponding signed binary value. The
   --  exception Constraint_Error is raised if the input is invalid.

   procedure Int32_To_Packed (V : Integer_32; P : System.Address; D : D32);
   --  The argument V is a signed binary integer, which is converted to
   --  packed decimal format and stored using P, the address of a packed
   --  decimal item of D digits (D is in the range 1-9). Constraint_Error
   --  is raised if V is out of range of this number of digits.

   procedure Int64_To_Packed (V : Integer_64; P : System.Address; D : D64);
   --  The argument V is a signed binary integer, which is converted to
   --  packed decimal format and stored using P, the address of a packed
   --  decimal item of D digits (D is in the range 10-18). Constraint_Error
   --  is raised if V is out of range of this number of digits.

end Interfaces.Packed_Decimal;
