--*****************************************************************************
--
--                   Random Number Generators - Utils 
--
--                       AUTHOR:  Robert Walsh
--                       CLASS:   CSCI 375
--                       DATE:    September 14, 1995
--
--*****************************************************************************

with TEXT_IO;
package INTEGER_IO is new TEXT_IO.INTEGER_IO(INTEGER);
with TEXT_IO, INTEGER_IO;
use TEXT_IO, INTEGER_IO;

package Random is
  procedure InitRandom;
    -- WHAT:	This procedure will prompt the user for an integer.  The
     --   	value of the integer will be used as the initial seed value of
     --		the random number generator.  In the event that the user
     --		provides an unacceptable input, the value of the seed will be
     --		assigned 44449.  The program notifies the user of the change.
     --		The procedure also initializes the randomness by calling the
     --		random number generator routine 15 times.
    -- IN:	None		
    -- OUT:	None

  function RangeRand(Limit : INTEGER) return INTEGER;
    -- WHAT:	This function creates a random number within a specified range. 
     --		The number generated will be > 0 and <= Limit. Uses GetRand().
    -- IN:	The upper Limit [INTEGER] for the range of random numbers.	
    -- OUT:     A random number [INTEGER] of the specified range; not
     --		including zero.

  procedure GetRand(Rand : out FLOAT);
    -- WHAT:	This procedure creates a positive random number [FLOAT] which
     --		is less than 1 including 0. Uses linear congruential algorithm
    -- IN:	None
    -- OUT:	Random number [FLOAT] >= 0 but < 1.

end Random;                            

Package body Random is
	Seed : INTEGER;   -- Arbitrary number used to manipulate a random #
      	  
	procedure InitRandom is
	Dumb : FLOAT;     -- Throw away random values    

	begin
		PUT("Please enter a seed value... ");
		GET (Seed);
		for I in 1..15 loop
		  GetRand(Dumb);    -- gives the random routine a 'warm start'
		end loop;
		exception
		  when others =>
		      PUT_LINE("Input error - Seed assigned value 44449");
		      Seed := 44449; -- If ANYTHING goes wrong: Seed = 44449
	end InitRandom;
	
	function RangeRand(Limit : INTEGER) return INTEGER is
	Rand : FLOAT;  -- holds random number < 1 and >= 0
	begin
	  GetRand(Rand);  -- Base for random number
	  return INTEGER(Rand*FLOAT(Limit-1))+1;  -- Compute random range value
	end RangeRand;
   
	procedure GetRand(Rand : out FLOAT) is
	Divider, Multiplier, Adder : INTEGER;
         -- Divider, Multiplier, Adder are values used in creating a random #
	begin
		Divider := 65535;     -- 2^n on n bit machine
		Multiplier := 15625;  -- Arbitrary add int < Divider 
		Adder := 22221;       -- Arbitrary odd int < Divider
		Seed := (Multiplier * Seed + Adder) mod Divider;
		Rand := FLOAT(Seed) / FLOAT(Divider - 1);
		exception
		  when others =>
		    -- usually constraint error generated by initial input
		    -- we will fix by reseting Seed
		    Seed := 44449;  -- if error occurs, reset random routine
	end GetRand;
begin
null;   -- Hey, this pakage is only simple random number subroutines
end Random;