gcc/ada/g-mbflra.adb

   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 --                                 B o d y                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2010, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 with Ada.Calendar;
  33
  34 package body GNAT.MBBS_Float_Random is
  35
  36    -------------------------
  37    -- Implementation Note --
  38    -------------------------
  39
  40    --  The design of this spec is a bit awkward, as a result of Ada 95 not
  41    --  permitting in-out parameters for function formals (most naturally
  42    --  Generator values would be passed this way). In pure Ada 95, the only
  43    --  solution would be to add a self-referential component to the generator
  44    --  allowing access to the generator object from inside the function. This
  45    --  would work because the generator is limited, which prevents any copy.
  46
  47    --  This is a bit heavy, so what we do is to use Unrestricted_Access to
  48    --  get a pointer to the state in the passed Generator. This works because
  49    --  Generator is a limited type and will thus always be passed by reference.
  50
  51    package Calendar renames Ada.Calendar;
  52
  53    type Pointer is access all State;
  54
  55    -----------------------
  56    -- Local Subprograms --
  57    -----------------------
  58
  59    procedure Euclid (P, Q : Int; X, Y : out Int; GCD : out Int);
  60
  61    function  Euclid (P, Q : Int) return Int;
  62
  63    function Square_Mod_N (X, N : Int) return Int;
  64
  65    ------------
  66    -- Euclid --
  67    ------------
  68
  69    procedure Euclid (P, Q : Int; X, Y : out Int; GCD : out Int) is
  70
  71       XT : Int := 1;
  72       YT : Int := 0;
  73
  74       procedure Recur
  75         (P,  Q  : Int;                    --  a (i-1), a (i)
  76          X,  Y  : Int;                    --  x (i),   y (i)
  77          XP, YP : in out Int;             --  x (i-1), y (i-1)
  78          GCD    : out Int);
  79
  80       procedure Recur
  81         (P,  Q  : Int;
  82          X,  Y  : Int;
  83          XP, YP : in out Int;
  84          GCD    : out Int)
  85       is
  86          Quo : Int := P / Q;              --  q <-- |_ a (i-1) / a (i) _|
  87          XT  : Int := X;                  --  x (i)
  88          YT  : Int := Y;                  --  y (i)
  89
  90       begin
  91          if P rem Q = 0 then                 --  while does not divide
  92             GCD := Q;
  93             XP  := X;
  94             YP  := Y;
  95          else
  96             Recur (Q, P - Q * Quo, XP - Quo * X, YP - Quo * Y, XT, YT, Quo);
  97
  98             --  a (i) <== a (i)
  99             --  a (i+1) <-- a (i-1) - q*a (i)
 100             --  x (i+1) <-- x (i-1) - q*x (i)
 101             --  y (i+1) <-- y (i-1) - q*y (i)
 102             --  x (i) <== x (i)
 103             --  y (i) <== y (i)
 104
 105             XP  := XT;
 106             YP  := YT;
 107             GCD := Quo;
 108          end if;
 109       end Recur;
 110
 111    --  Start of processing for Euclid
 112
 113    begin
 114       Recur (P, Q, 0, 1, XT, YT, GCD);
 115       X := XT;
 116       Y := YT;
 117    end Euclid;
 118
 119    function Euclid (P, Q : Int) return Int is
 120       X, Y, GCD : Int;
 121       pragma Unreferenced (Y, GCD);
 122    begin
 123       Euclid (P, Q, X, Y, GCD);
 124       return X;
 125    end Euclid;
 126
 127    -----------
 128    -- Image --
 129    -----------
 130
 131    function Image (Of_State : State) return String is
 132    begin
 133       return Int'Image (Of_State.X1) & ',' & Int'Image (Of_State.X2)
 134              & ',' &
 135              Int'Image (Of_State.P)  & ',' & Int'Image (Of_State.Q);
 136    end Image;
 137
 138    ------------
 139    -- Random --
 140    ------------
 141
 142    function Random  (Gen : Generator) return Uniformly_Distributed is
 143       Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
 144
 145    begin
 146       Genp.X1 := Square_Mod_N (Genp.X1,  Genp.P);
 147       Genp.X2 := Square_Mod_N (Genp.X2,  Genp.Q);
 148       return
 149         Float ((Flt (((Genp.X2 - Genp.X1) * Genp.X)
 150                   mod Genp.Q) * Flt (Genp.P)
 151           + Flt (Genp.X1)) * Genp.Scl);
 152    end Random;
 153
 154    -----------
 155    -- Reset --
 156    -----------
 157
 158    --  Version that works from given initiator value
 159
 160    procedure Reset (Gen : Generator; Initiator : Integer) is
 161       Genp   : constant Pointer := Gen.Gen_State'Unrestricted_Access;
 162       X1, X2 : Int;
 163
 164    begin
 165       X1 := 2 + Int (Initiator) mod (K1 - 3);
 166       X2 := 2 + Int (Initiator) mod (K2 - 3);
 167
 168       --  Eliminate effects of small initiators
 169
 170       for J in 1 .. 5 loop
 171          X1 := Square_Mod_N (X1, K1);
 172          X2 := Square_Mod_N (X2, K2);
 173       end loop;
 174
 175       Genp.all :=
 176         (X1  => X1,
 177          X2  => X2,
 178          P   => K1,
 179          Q   => K2,
 180          X   => 1,
 181          Scl => Scal);
 182    end Reset;
 183
 184    --  Version that works from specific saved state
 185
 186    procedure Reset (Gen : Generator; From_State : State) is
 187       Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
 188
 189    begin
 190       Genp.all := From_State;
 191    end Reset;
 192
 193    --  Version that works from calendar
 194
 195    procedure Reset (Gen : Generator) is
 196       Genp   : constant Pointer       := Gen.Gen_State'Unrestricted_Access;
 197       Now    : constant Calendar.Time := Calendar.Clock;
 198       X1, X2 : Int;
 199
 200    begin
 201       X1 := Int (Calendar.Year  (Now)) * 12 * 31 +
 202             Int (Calendar.Month (Now)) * 31 +
 203             Int (Calendar.Day   (Now));
 204
 205       X2 := Int (Calendar.Seconds (Now) * Duration (1000.0));
 206
 207       X1 := 2 + X1 mod (K1 - 3);
 208       X2 := 2 + X2 mod (K2 - 3);
 209
 210       --  Eliminate visible effects of same day starts
 211
 212       for J in 1 .. 5 loop
 213          X1 := Square_Mod_N (X1, K1);
 214          X2 := Square_Mod_N (X2, K2);
 215       end loop;
 216
 217       Genp.all :=
 218         (X1  => X1,
 219          X2  => X2,
 220          P   => K1,
 221          Q   => K2,
 222          X   => 1,
 223          Scl => Scal);
 224
 225    end Reset;
 226
 227    ----------
 228    -- Save --
 229    ----------
 230
 231    procedure Save (Gen : Generator; To_State : out State) is
 232    begin
 233       To_State := Gen.Gen_State;
 234    end Save;
 235
 236    ------------------
 237    -- Square_Mod_N --
 238    ------------------
 239
 240    function Square_Mod_N (X, N : Int) return Int is
 241       Temp : constant Flt := Flt (X) * Flt (X);
 242       Div  : Int;
 243
 244    begin
 245       Div := Int (Temp / Flt (N));
 246       Div := Int (Temp - Flt (Div) * Flt (N));
 247
 248       if Div < 0 then
 249          return Div + N;
 250       else
 251          return Div;
 252       end if;
 253    end Square_Mod_N;
 254
 255    -----------
 256    -- Value --
 257    -----------
 258
 259    function Value (Coded_State : String) return State is
 260       Last  : constant Natural := Coded_State'Last;
 261       Start : Positive := Coded_State'First;
 262       Stop  : Positive := Coded_State'First;
 263       Outs  : State;
 264
 265    begin
 266       while Stop <= Last and then Coded_State (Stop) /= ',' loop
 267          Stop := Stop + 1;
 268       end loop;
 269
 270       if Stop > Last then
 271          raise Constraint_Error;
 272       end if;
 273
 274       Outs.X1 := Int'Value (Coded_State (Start .. Stop - 1));
 275       Start := Stop + 1;
 276
 277       loop
 278          Stop := Stop + 1;
 279          exit when Stop > Last or else Coded_State (Stop) = ',';
 280       end loop;
 281
 282       if Stop > Last then
 283          raise Constraint_Error;
 284       end if;
 285
 286       Outs.X2 := Int'Value (Coded_State (Start .. Stop - 1));
 287       Start := Stop + 1;
 288
 289       loop
 290          Stop := Stop + 1;
 291          exit when Stop > Last or else Coded_State (Stop) = ',';
 292       end loop;
 293
 294       if Stop > Last then
 295          raise Constraint_Error;
 296       end if;
 297
 298       Outs.P   := Int'Value (Coded_State (Start .. Stop - 1));
 299       Outs.Q   := Int'Value (Coded_State (Stop + 1 .. Last));
 300       Outs.X   := Euclid (Outs.P, Outs.Q);
 301       Outs.Scl := 1.0 / (Flt (Outs.P) * Flt (Outs.Q));
 302
 303       --  Now do *some* sanity checks
 304
 305       if Outs.Q < 31 or else Outs.P < 31
 306         or else Outs.X1 not in 2 .. Outs.P - 1
 307         or else Outs.X2 not in 2 .. Outs.Q - 1
 308       then
 309          raise Constraint_Error;
 310       end if;
 311
 312       return Outs;
 313    end Value;
 314 end GNAT.MBBS_Float_Random;