gcc/ada/libgnat/g-mbdira.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --            G N A T . M B B S _ D I S C R E T E _ R A N D O M             --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2023, 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 Robert
  37 --  Eachus. It is based on the work of L. Blum, M. Blum, and M. Shub, SIAM
  38 --  Journal of Computing, Vol 15. No 2, May 1986. The particular choices for P
  39 --  and Q chosen here guarantee a period of 562,085,314,430,582 (about 2**49),
  40 --  and the generated sequence has excellent randomness properties. For further
  41 --  details, see the paper "Fast Generation of Trustworthy Random Numbers", by
  42 --  Robert Eachus, which describes both the algorithm and the efficient
  43 --  implementation approach used here.
  44
  45 --  Formerly, this package was Ada.Numerics.Discrete_Random. It is retained
  46 --  here in part to allow users to reconstruct number sequences generated
  47 --  by previous versions.
  48
  49 with Interfaces;
  50
  51 generic
  52    type Result_Subtype is (<>);
  53
  54 package GNAT.MBBS_Discrete_Random is
  55
  56    --  The algorithm used here is reliable from a required statistical point of
  57    --  view only up to 48 bits. We try to behave reasonably in the case of
  58    --  larger types, but we can't guarantee the required properties. So
  59    --  generate a warning for these (slightly) dubious cases.
  60
  61    pragma Compile_Time_Warning
  62      (Result_Subtype'Size > 48,
  63       "statistical properties not guaranteed for size > 48");
  64
  65    --  Basic facilities
  66
  67    type Generator is limited private;
  68
  69    function Random (Gen : Generator) return Result_Subtype;
  70
  71    procedure Reset (Gen : Generator);
  72    procedure Reset (Gen : Generator; Initiator : Integer);
  73
  74    --  Advanced facilities
  75
  76    type State is private;
  77
  78    procedure Save  (Gen : Generator; To_State   : out State);
  79    procedure Reset (Gen : Generator; From_State : State);
  80
  81    Max_Image_Width : constant := 80;
  82
  83    function Image (Of_State    : State)  return String;
  84    function Value (Coded_State : String) return State;
  85
  86 private
  87    subtype Int is Interfaces.Integer_32;
  88    subtype Rst is Result_Subtype;
  89
  90    --  We prefer to use 14 digits for Flt, but some targets are more limited
  91
  92    type Flt is digits Positive'Min (14, Long_Long_Float'Digits);
  93
  94    RstF : constant Flt := Flt (Rst'Pos (Rst'First));
  95    RstL : constant Flt := Flt (Rst'Pos (Rst'Last));
  96
  97    Offs : constant Flt := RstF - 0.5;
  98
  99    K1   : constant := 94_833_359;
 100    K1F  : constant := 94_833_359.0;
 101    K2   : constant := 47_416_679;
 102    K2F  : constant := 47_416_679.0;
 103    Scal : constant Flt := (RstL - RstF + 1.0) / (K1F * K2F);
 104
 105    type State is record
 106       X1  : Int := Int (2999 ** 2);
 107       X2  : Int := Int (1439 ** 2);
 108       P   : Int := K1;
 109       Q   : Int := K2;
 110       FP  : Flt := K1F;
 111       Scl : Flt := Scal;
 112    end record;
 113
 114    type Writable_Access (Self : access Generator) is limited null record;
 115    --  Auxiliary type to make Generator a self-referential type
 116
 117    type Generator is limited record
 118       Writable  : Writable_Access (Generator'Access);
 119       --  This self reference allows functions to modify Generator arguments
 120       Gen_State : State;
 121    end record;
 122
 123 end GNAT.MBBS_Discrete_Random;