gcc/ada/a-nudira.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUNTIME COMPONENTS                          --
   4 --                                                                          --
   5 --         A D A . N U M E R I C S . D I S C R E T E _ R A N D O M          --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --                            $Revision: 1.17 $
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  24 -- As a special exception,  if other files  instantiate  generics from this --
  25 -- unit, or you link  this unit with other files  to produce an executable, --
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  32 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
  33 --                                                                          --
  34 ------------------------------------------------------------------------------
  35
  36 with Ada.Calendar;
  37 with Interfaces; use Interfaces;
  38
  39 package body Ada.Numerics.Discrete_Random is
  40
  41    -------------------------
  42    -- Implementation Note --
  43    -------------------------
  44
  45    --  The design of this spec is very awkward, as a result of Ada 95 not
  46    --  permitting in-out parameters for function formals (most naturally
  47    --  Generator values would be passed this way). In pure Ada 95, the only
  48    --  solution is to use the heap and pointers, and, to avoid memory leaks,
  49    --  controlled types.
  50
  51    --  This is awfully heavy, so what we do is to use Unrestricted_Access to
  52    --  get a pointer to the state in the passed Generator. This works because
  53    --  Generator is a limited type and will thus always be passed by reference.
  54
  55    type Pointer is access all State;
  56
  57    Need_64 : constant Boolean := Rst'Pos (Rst'Last) > Int'Last;
  58
  59    -----------------------
  60    -- Local Subprograms --
  61    -----------------------
  62
  63    function Square_Mod_N (X, N : Int) return Int;
  64    pragma Inline (Square_Mod_N);
  65    --  Computes X**2 mod N avoiding intermediate overflow
  66
  67    -----------
  68    -- Image --
  69    -----------
  70
  71    function Image (Of_State : State) return String is
  72    begin
  73       return Int'Image (Of_State.X1) &
  74              ','                            &
  75              Int'Image (Of_State.X2) &
  76              ','                            &
  77              Int'Image (Of_State.Q);
  78    end Image;
  79
  80    ------------
  81    -- Random --
  82    ------------
  83
  84    function Random (Gen : Generator) return Rst is
  85       Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
  86       Temp : Int;
  87       TF   : Flt;
  88
  89    begin
  90       --  Check for flat range here, since we are typically run with checks
  91       --  off, note that in practice, this condition will usually be static
  92       --  so we will not actually generate any code for the normal case.
  93
  94       if Rst'Last < Rst'First then
  95          raise Constraint_Error;
  96       end if;
  97
  98       --  Continue with computation if non-flat range
  99
 100       Genp.X1 := Square_Mod_N (Genp.X1, Genp.P);
 101       Genp.X2 := Square_Mod_N (Genp.X2, Genp.Q);
 102       Temp := Genp.X2 - Genp.X1;
 103
 104       --  Following duplication is not an error, it is a loop unwinding!
 105
 106       if Temp < 0 then
 107          Temp := Temp + Genp.Q;
 108       end if;
 109
 110       if Temp < 0 then
 111          Temp := Temp + Genp.Q;
 112       end if;
 113
 114       TF :=  Offs + (Flt (Temp) * Flt (Genp.P) + Flt (Genp.X1)) * Genp.Scl;
 115
 116       --  Pathological, but there do exist cases where the rounding implicit
 117       --  in calculating the scale factor will cause rounding to 'Last + 1.
 118       --  In those cases, returning 'First results in the least bias.
 119
 120       if TF >= Flt (Rst'Pos (Rst'Last)) + 0.5 then
 121          return Rst'First;
 122
 123       elsif Need_64 then
 124          return Rst'Val (Interfaces.Integer_64 (TF));
 125
 126       else
 127          return Rst'Val (Int (TF));
 128       end if;
 129
 130    end Random;
 131
 132    -----------
 133    -- Reset --
 134    -----------
 135
 136    procedure Reset (Gen : Generator; Initiator : Integer) is
 137       Genp   : constant Pointer := Gen.Gen_State'Unrestricted_Access;
 138       X1, X2 : Int;
 139
 140    begin
 141       X1 := 2 + Int (Initiator) mod (K1 - 3);
 142       X2 := 2 + Int (Initiator) mod (K2 - 3);
 143
 144       for J in 1 .. 5 loop
 145          X1 := Square_Mod_N (X1, K1);
 146          X2 := Square_Mod_N (X2, K2);
 147       end loop;
 148
 149       --  eliminate effects of small Initiators.
 150
 151       Genp.all :=
 152         (X1  => X1,
 153          X2  => X2,
 154          P   => K1,
 155          Q   => K2,
 156          FP  => K1F,
 157          Scl => Scal);
 158    end Reset;
 159
 160    -----------
 161    -- Reset --
 162    -----------
 163
 164    procedure Reset (Gen : Generator) is
 165       Genp : constant Pointer       := Gen.Gen_State'Unrestricted_Access;
 166       Now  : constant Calendar.Time := Calendar.Clock;
 167       X1   : Int;
 168       X2   : Int;
 169
 170    begin
 171       X1 := Int (Calendar.Year    (Now)) * 12 * 31 +
 172             Int (Calendar.Month   (Now) * 31)     +
 173             Int (Calendar.Day     (Now));
 174
 175       X2 := Int (Calendar.Seconds (Now) * Duration (1000.0));
 176
 177       X1 := 2 + X1 mod (K1 - 3);
 178       X2 := 2 + X2 mod (K2 - 3);
 179
 180       --  Eliminate visible effects of same day starts
 181
 182       for J in 1 .. 5 loop
 183          X1 := Square_Mod_N (X1, K1);
 184          X2 := Square_Mod_N (X2, K2);
 185       end loop;
 186
 187       Genp.all :=
 188         (X1  => X1,
 189          X2  => X2,
 190          P   => K1,
 191          Q   => K2,
 192          FP  => K1F,
 193          Scl => Scal);
 194
 195    end Reset;
 196
 197    -----------
 198    -- Reset --
 199    -----------
 200
 201    procedure Reset (Gen : Generator; From_State : State) is
 202       Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
 203
 204    begin
 205       Genp.all := From_State;
 206    end Reset;
 207
 208    ----------
 209    -- Save --
 210    ----------
 211
 212    procedure Save (Gen : Generator; To_State : out State) is
 213    begin
 214       To_State := Gen.Gen_State;
 215    end Save;
 216
 217    ------------------
 218    -- Square_Mod_N --
 219    ------------------
 220
 221    function Square_Mod_N (X, N : Int) return Int is
 222    begin
 223       return Int ((Integer_64 (X) ** 2) mod (Integer_64 (N)));
 224    end Square_Mod_N;
 225
 226    -----------
 227    -- Value --
 228    -----------
 229
 230    function Value (Coded_State : String) return State is
 231       Start : Positive := Coded_State'First;
 232       Stop  : Positive := Coded_State'First;
 233       Outs  : State;
 234
 235    begin
 236       while Coded_State (Stop) /= ',' loop
 237          Stop := Stop + 1;
 238       end loop;
 239
 240       Outs.X1 := Int'Value (Coded_State (Start .. Stop - 1));
 241       Start := Stop + 1;
 242
 243       loop
 244          Stop := Stop + 1;
 245          exit when Coded_State (Stop) = ',';
 246       end loop;
 247
 248       Outs.X2  := Int'Value (Coded_State (Start .. Stop - 1));
 249       Outs.Q   := Int'Value (Coded_State (Stop + 1 .. Coded_State'Last));
 250       Outs.P   := Outs.Q * 2 + 1;
 251       Outs.FP  := Flt (Outs.P);
 252       Outs.Scl := (RstL - RstF + 1.0) / (Flt (Outs.P) * Flt (Outs.Q));
 253
 254       --  Now do *some* sanity checks.
 255
 256       if Outs.Q < 31
 257         or else Outs.X1 not in 2 .. Outs.P - 1
 258         or else Outs.X2 not in 2 .. Outs.Q - 1
 259       then
 260          raise Constraint_Error;
 261       end if;
 262
 263       return Outs;
 264    end Value;
 265
 266 end Ada.Numerics.Discrete_Random;