1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUN-TIME COMPONENTS                         --
4--                                                                          --
5--               G N A T . M B B S _ F L O A T _ R A N D O M                --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--          Copyright (C) 1992-2018, Free Software Foundation, Inc.         --
10--                                                                          --
11-- This specification is derived from the Ada Reference Manual for use with --
12-- GNAT. The copyright notice above, and the license provisions that follow --
13-- apply solely to the  contents of the part following the private keyword. --
14--                                                                          --
15-- GNAT is free software;  you can  redistribute it  and/or modify it under --
16-- terms of the  GNU General Public License as published  by the Free Soft- --
17-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
18-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
19-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
20-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
21--                                                                          --
22-- As a special exception under Section 7 of GPL version 3, you are granted --
23-- additional permissions described in the GCC Runtime Library Exception,   --
24-- version 3.1, as published by the Free Software Foundation.               --
25--                                                                          --
26-- You should have received a copy of the GNU General Public License and    --
27-- a copy of the GCC Runtime Library Exception along with this program;     --
28-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
29-- <http://www.gnu.org/licenses/>.                                          --
30--                                                                          --
31-- GNAT was originally developed  by the GNAT team at  New York University. --
32-- Extensive contributions were provided by Ada Core Technologies Inc.      --
33--                                                                          --
34------------------------------------------------------------------------------
35
36--  The implementation used in this package was contributed by
37--  Robert Eachus. It is based on the work of L. Blum, M. Blum, and
38--  M. Shub, SIAM Journal of Computing, Vol 15. No 2, May 1986. The
39--  particular choices for P and Q chosen here guarantee a period of
40--  562,085,314,430,582 (about 2**49), and the generated sequence has
41--  excellent randomness properties. For further details, see the
42--  paper "Fast Generation of Trustworthy Random Numbers", by Robert
43--  Eachus, which describes both the algorithm and the efficient
44--  implementation approach used here.
45
46--  Formerly, this package was Ada.Numerics.Float_Random. It is retained
47--  here in part to allow users to reconstruct number sequences generated
48--  by previous versions.
49
50with Interfaces;
51
52package GNAT.MBBS_Float_Random is
53
54   --  Basic facilities
55
56   type Generator is limited private;
57
58   subtype Uniformly_Distributed is Float range 0.0 .. 1.0;
59
60   function Random (Gen : Generator) return Uniformly_Distributed;
61
62   procedure Reset (Gen : Generator);
63   procedure Reset (Gen : Generator; Initiator : Integer);
64
65   --  Advanced facilities
66
67   type State is private;
68
69   procedure Save  (Gen : Generator; To_State   : out State);
70   procedure Reset (Gen : Generator; From_State : State);
71
72   Max_Image_Width : constant := 80;
73
74   function Image (Of_State    : State)  return String;
75   function Value (Coded_State : String) return State;
76
77private
78   type Int is new Interfaces.Integer_32;
79
80   --  We prefer to use 14 digits for Flt, but some targets are more limited
81
82   type Flt is digits Positive'Min (14, Long_Long_Float'Digits);
83
84   K1   : constant := 94_833_359;
85   K1F  : constant := 94_833_359.0;
86   K2   : constant := 47_416_679;
87   K2F  : constant := 47_416_679.0;
88   Scal : constant := 1.0 / (K1F * K2F);
89
90   type State is record
91      X1  : Int := 2999 ** 2;      --  Square mod p
92      X2  : Int := 1439 ** 2;      --  Square mod q
93      P   : Int := K1;
94      Q   : Int := K2;
95      X   : Int := 1;
96      Scl : Flt := Scal;
97   end record;
98
99   type Generator is limited record
100      Gen_State : State;
101   end record;
102
103end GNAT.MBBS_Float_Random;
104