Module Random

src/Random.Mod

@@ -0,0 +1,42 @@
+MODULE Random;
+IMPORT Platform;
+CONST modulo* = 2147483647; (* =2^31-1 *)
+VAR seed*: INTEGER;
+
+PROCEDURE Time(): INTEGER;
+RETURN Platform.Time() END Time;
+
+(* Set random seed value. Any values are allowed, although
+   values not in [1..2^31-2] will be mapped into this range. *)
+PROCEDURE PutSeed*(newSeed: INTEGER);
+BEGIN newSeed := newSeed MOD modulo;
+  IF newSeed = 0 THEN seed := 1 ELSE seed := newSeed END
+END PutSeed;
+
+PROCEDURE NextRND;
+CONST a = 16807;
+  q = 127773; (* m div a *)
+  r = 2836;   (* m mod a *)
+VAR lo, hi, test: INTEGER;
+BEGIN hi := seed DIV q; lo := seed MOD q;
+  test := a * lo - r * hi;
+  IF test > 0 THEN seed := test ELSE seed := test + modulo END
+END NextRND;
+
+(* Calculates a new number. range has to be included in
+   [1..2^31-2]. Result is a number from 0, 1, ... , range-1. *)
+PROCEDURE Int*(range: INTEGER): INTEGER;
+BEGIN NextRND
+RETURN seed MOD range END Int;
+
+(* Calculates a number x with 0.0 <= x < 1.0. *)
+PROCEDURE Uniform*(): REAL;
+BEGIN NextRND
+RETURN (seed - 1) * (1 / (modulo - 1)) END Uniform;
+
+PROCEDURE Randomize*;
+BEGIN PutSeed(Time())
+END Randomize;
+
+BEGIN Randomize
+END Random.