1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT COMPILER COMPONENTS                         --
4--                                                                          --
5--            I N T E R F A C E S . P A C K E D _ D E C I M A L             --
6--                                                                          --
7--                                 S p e c                                  --
8--            (Version for IBM Mainframe Packed Decimal Format)             --
9--                                                                          --
10--          Copyright (C) 1992-2019, Free Software Foundation, Inc.         --
11--                                                                          --
12-- GNAT is free software;  you can  redistribute it  and/or modify it under --
13-- terms of the  GNU General Public License as published  by the Free Soft- --
14-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
15-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
16-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
17-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
18--                                                                          --
19-- As a special exception under Section 7 of GPL version 3, you are granted --
20-- additional permissions described in the GCC Runtime Library Exception,   --
21-- version 3.1, as published by the Free Software Foundation.               --
22--                                                                          --
23-- You should have received a copy of the GNU General Public License and    --
24-- a copy of the GCC Runtime Library Exception along with this program;     --
25-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
26-- <http://www.gnu.org/licenses/>.                                          --
27--                                                                          --
28-- GNAT was originally developed  by the GNAT team at  New York University. --
29-- Extensive contributions were provided by Ada Core Technologies Inc.      --
30--                                                                          --
31------------------------------------------------------------------------------
32
33--  This unit defines the packed decimal format used by GNAT in response to
34--  a specification of Machine_Radix 10 for a decimal fixed-point type. The
35--  format and operations are completely encapsulated in this unit, so all
36--  that is necessary to compile using different packed decimal formats is
37--  to replace this single unit.
38
39--  Note that the compiler access the spec of this unit during compilation
40--  to obtain the data length that needs allocating, so the correct version
41--  of the spec must be available to the compiler, and must correspond to
42--  the spec and body made available to the linker, and all units of a given
43--  program must be compiled with the same version of the spec and body.
44--  This consistency will be enforced automatically using the normal binder
45--  consistency checking, since any unit declaring Machine_Radix 10 types or
46--  containing operations on such data will implicitly with Packed_Decimal.
47
48with System;
49
50package Interfaces.Packed_Decimal is
51
52   ------------------------
53   -- Format Description --
54   ------------------------
55
56   --  IBM Mainframe packed decimal format uses a byte string of length one
57   --  to 10 bytes, with the most significant byte first. Each byte contains
58   --  two decimal digits (with the high order digit in the left nibble, and
59   --  the low order four bits contain the sign, using the following code:
60
61   --     16#A#  2#1010#   positive
62   --     16#B#  2#1011#   negative
63   --     16#C#  2#1100#   positive (preferred representation)
64   --     16#D#  2#1101#   negative (preferred representation)
65   --     16#E#  2#1110#   positive
66   --     16#F#  2#1011#   positive
67
68   --  In this package, all six sign representations are interpreted as
69   --  shown above when an operand is read, when an operand is written,
70   --  the preferred representations are always used. Constraint_Error
71   --  is raised if any other bit pattern is found in the sign nibble,
72   --  or if a digit nibble contains an invalid digit code.
73
74   --  Some examples follow:
75
76   --     05 76 3C      +5763
77   --     00 01 1D        -11
78   --     00 04 4E        +44 (non-standard sign)
79   --     00 00 00      invalid (incorrect sign nibble)
80   --     0A 01 1C      invalid (bad digit)
81
82   ------------------
83   -- Length Array --
84   ------------------
85
86   --  The following array must be declared in exactly the form shown, since
87   --  the compiler accesses the associated tree to determine the size to be
88   --  allocated to a machine radix 10 type, depending on the number of digits.
89
90   subtype Byte_Length is Positive range 1 .. 10;
91   --  Range of possible byte lengths
92
93   Packed_Size : constant array (1 .. 18) of Byte_Length :=
94      (01 => 01,    -- Length in bytes for digits 1
95       02 => 02,    -- Length in bytes for digits 2
96       03 => 02,    -- Length in bytes for digits 2
97       04 => 03,    -- Length in bytes for digits 2
98       05 => 03,    -- Length in bytes for digits 2
99       06 => 04,    -- Length in bytes for digits 2
100       07 => 04,    -- Length in bytes for digits 2
101       08 => 05,    -- Length in bytes for digits 2
102       09 => 05,    -- Length in bytes for digits 2
103       10 => 06,    -- Length in bytes for digits 2
104       11 => 06,    -- Length in bytes for digits 2
105       12 => 07,    -- Length in bytes for digits 2
106       13 => 07,    -- Length in bytes for digits 2
107       14 => 08,    -- Length in bytes for digits 2
108       15 => 08,    -- Length in bytes for digits 2
109       16 => 09,    -- Length in bytes for digits 2
110       17 => 09,    -- Length in bytes for digits 2
111       18 => 10);   -- Length in bytes for digits 2
112
113   -------------------------
114   -- Conversion Routines --
115   -------------------------
116
117   subtype D32 is Positive range 1 .. 9;
118   --  Used to represent number of digits in a packed decimal value that
119   --  can be represented in a 32-bit binary signed integer form.
120
121   subtype D64 is Positive range 10 .. 18;
122   --  Used to represent number of digits in a packed decimal value that
123   --  requires a 64-bit signed binary integer for representing all values.
124
125   function Packed_To_Int32 (P : System.Address; D : D32) return Integer_32;
126   --  The argument P is the address of a packed decimal value and D is the
127   --  number of digits (in the range 1 .. 9, as implied by the subtype).
128   --  The returned result is the corresponding signed binary value. The
129   --  exception Constraint_Error is raised if the input is invalid.
130
131   function Packed_To_Int64 (P : System.Address; D : D64) return Integer_64;
132   --  The argument P is the address of a packed decimal value and D is the
133   --  number of digits (in the range 10 .. 18, as implied by the subtype).
134   --  The returned result is the corresponding signed binary value. The
135   --  exception Constraint_Error is raised if the input is invalid.
136
137   procedure Int32_To_Packed (V : Integer_32; P : System.Address; D : D32);
138   --  The argument V is a signed binary integer, which is converted to
139   --  packed decimal format and stored using P, the address of a packed
140   --  decimal item of D digits (D is in the range 1-9). Constraint_Error
141   --  is raised if V is out of range of this number of digits.
142
143   procedure Int64_To_Packed (V : Integer_64; P : System.Address; D : D64);
144   --  The argument V is a signed binary integer, which is converted to
145   --  packed decimal format and stored using P, the address of a packed
146   --  decimal item of D digits (D is in the range 10-18). Constraint_Error
147   --  is raised if V is out of range of this number of digits.
148
149end Interfaces.Packed_Decimal;
150