indexing
	description: "Provides a random number generator instance"
	license: "MIT license (see ../license.txt)"
	author: "Beat Strasser <beat@stradax.net>"
	date: "$Date$"
	revision: "$Revision$"

class
	P2P_RANDOM_SHARED

inherit
	DT_SHARED_SYSTEM_CLOCK
		export
			{NONE} all
		end

feature {NONE} -- Implementation

	rand: RANDOM is
			-- Create unique random number generator and seed with number of seconds since epoch
		indexing
			once_status: global
		local
			seed: NATURAL_64
			seed_32: INTEGER
			cur_time: DT_DATE_TIME
		once
			cur_time := utc_system_clock.date_time_now

				-- Compute the seed as the number of milliseconds sind the beginning of unix timestamp.
			seed := cur_time.day_count.to_natural_64 * cur_time.seconds_in_day.to_natural_64 + cur_time.second_count.to_natural_64
			seed := seed * 1000 + cur_time.millisecond.to_natural_64

				-- this trick from RFC 4122 helps to preserve more meaning of 64bit integer to a 32bit integer
			seed_32 := ((seed |>> 32).bit_xor (seed).as_integer_32 & 0x7FFFFFFF)

			create Result.set_seed (seed_32)
			Result.start
		end

end