indexing
	description: "Pseudo-random number sequence, linear congruential method"
	status: "See notice at end of class"
	names: random
	date: "$Date$"
	revision: "$Revision$"

class interface
	RANDOM

create

	make
			-- Initialize structure using a default seed.
		ensure
			seed_set: seed = default_seed

	set_seed (s: INTEGER)
			-- Initialize sequence using s as the seed.
		require
			non_negative: s >= 0
		ensure
			seed_set: seed = s

feature -- Initialization

	make
			-- Initialize structure using a default seed.
		ensure
			seed_set: seed = default_seed

	set_seed (s: INTEGER)
			-- Initialize sequence using s as the seed.
		require
			non_negative: s >= 0
		ensure
			seed_set: seed = s

feature -- Access

	default_seed: INTEGER
			-- Default value 123,457;
			-- may be redefined for a new generator.

	double_i_th (i: INTEGER): DOUBLE
			-- The i-th random number as a double between 0 and 1

	double_item: DOUBLE
			-- The current random number as a double between 0 and 1

	has (n: INTEGER): BOOLEAN
			-- Will n be part of the random number sequence?
		ensure -- from CONTAINER
			not_found_in_empty: Result implies not is_empty
		ensure then
			only_: Result = (n < modulus and n >= 0)

	i_th (i: INTEGER): INTEGER
			-- The i-th random number
		require -- from COUNTABLE
			positive_argument: i > 0
		ensure then
			in_range: (Result < modulus) and (Result >= 0)

	increment: INTEGER
			-- Default value 0;
			-- may be redefined for a new generator.

	index: INTEGER
			-- Index of current position
			-- (from COUNTABLE_SEQUENCE)

	index_of (v: like item; i: INTEGER): INTEGER
			-- Index of i-th occurrence of v.
			-- 0 if none.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)
		require -- from LINEAR
			positive_occurrences: i > 0
		ensure -- from LINEAR
			non_negative_result: Result >= 0

	item: INTEGER
			-- Item at current position
			-- (from COUNTABLE_SEQUENCE)
		require -- from TRAVERSABLE
			not_off: not off
		require -- from ACTIVE
			readable: readable

	modulus: INTEGER
			-- Default value 2^31 -1 = 2,147,483,647;
			-- may be redefined for a new generator.

	multiplier: INTEGER
			-- Default value 7^5 = 16,807;
			-- may be redefined for a new generator.

	next_random (n: INTEGER): INTEGER
			-- Next random number after n
			-- in pseudo-random order
		require
			in_range: (n < modulus) and (n >= 0)
		ensure
			in_range: (Result < modulus) and (Result >= 0)

	occurrences (v: INTEGER): INTEGER
			-- Number of times v appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)
		ensure -- from BAG
			non_negative_occurrences: Result >= 0

	real_i_th (i: INTEGER): REAL
			-- The i-th random number as a real between 0 and 1

	real_item: REAL
			-- The current random number as a real between 0 and 1

	search (v: like item)
			-- Move to first position (at or after current
			-- position) where item and v are equal.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- If no such position ensure that exhausted will be true.
			-- (from LINEAR)
		ensure -- from LINEAR
			object_found: (not exhausted and object_comparison) implies equal (v, item)
			item_found: (not exhausted and not object_comparison) implies v = item

	seed: INTEGER
			-- Seed for sequence.

feature -- Status report

	After: BOOLEAN is False
			-- Is current position past last item? (Answer: no.)
			-- (from COUNTABLE_SEQUENCE)

	changeable_comparison_criterion: BOOLEAN
			-- May object_comparison be changed?
			-- (Answer: yes by default.)
			-- (from CONTAINER)

	exhausted: BOOLEAN
			-- Has structure been completely explored?
			-- (from LINEAR)
		ensure -- from LINEAR
			exhausted_when_off: off implies Result

	Extendible: BOOLEAN is False
			-- May items be added? (Answer: no.)
			-- (from COUNTABLE_SEQUENCE)

	Full: BOOLEAN is True
			-- The structure is complete
			-- (from INFINITE)

	Is_empty: BOOLEAN is False
			-- Is structure empty? (Answer: no.)
			-- (from INFINITE)

	is_inserted (v: INTEGER): BOOLEAN
			-- Has v been inserted by the most recent insertion?
			-- (By default, the value returned is equivalent to calling
			-- `has (v)'. However, descendants might be able to provide more
			-- efficient implementations.)
			-- (from COLLECTION)

	object_comparison: BOOLEAN
			-- Must search operations use equal rather than =
			-- for comparing references? (Default: no, use =.)
			-- (from CONTAINER)

	off: BOOLEAN
			-- Is there no current item?
			-- (from LINEAR)

	Prunable: BOOLEAN is False
			-- May items be removed? (Answer: no.)
			-- (from COUNTABLE_SEQUENCE)

	Readable: BOOLEAN is True
			-- Is there a current item that may be read?
			-- (Answer: yes.)
			-- (from COUNTABLE_SEQUENCE)

	Writable: BOOLEAN is False
			-- Is there a current item that may be written?
			-- (Answer: no.)
			-- (from COUNTABLE_SEQUENCE)

feature -- Status setting

	compare_objects
			-- Ensure that future search operations will use equal
			-- rather than = for comparing references.
			-- (from CONTAINER)
		require -- from CONTAINER
			changeable_comparison_criterion
		ensure -- from CONTAINER
			object_comparison

	compare_references
			-- Ensure that future search operations will use =
			-- rather than equal for comparing references.
			-- (from CONTAINER)
		require -- from CONTAINER
			changeable_comparison_criterion
		ensure -- from CONTAINER
			reference_comparison: not object_comparison

feature -- Cursor movement

	forth
			-- Move to next position.
			-- (from COUNTABLE_SEQUENCE)
		require -- from LINEAR
			not_after: not after

	start
			-- Move to first position.
			-- (from COUNTABLE_SEQUENCE)

feature -- Iteration

	do_all (action: PROCEDURE [ANY, TUPLE [INTEGER]])
			-- Apply action to every item.
			-- Semantics not guaranteed if action changes the structure;
			-- in such a case, apply iterator to clone of structure instead.
			-- (from LINEAR)
		require -- from TRAVERSABLE
			action_exists: action /= void

	do_if (action: PROCEDURE [ANY, TUPLE [INTEGER]]; test: FUNCTION [ANY, TUPLE [INTEGER], BOOLEAN])
			-- Apply action to every item that satisfies test.
			-- Semantics not guaranteed if action or test changes the structure;
			-- in such a case, apply iterator to clone of structure instead.
			-- (from LINEAR)
		require -- from TRAVERSABLE
			action_exists: action /= void
			test_exits: test /= void

	for_all (test: FUNCTION [ANY, TUPLE [INTEGER], BOOLEAN]): BOOLEAN
			-- Is test true for all items?
			-- (from LINEAR)
		require -- from TRAVERSABLE
			test_exits: test /= void

	there_exists (test: FUNCTION [ANY, TUPLE [INTEGER], BOOLEAN]): BOOLEAN
			-- Is test true for at least one item?
			-- (from LINEAR)
		require -- from TRAVERSABLE
			test_exits: test /= void

invariant

	non_negative_seed: seed >= 0
	non_negative_increment: increment >= 0
	positive_multiplier: multiplier > 0
	modulus_constraint: modulus > 1
		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)
		-- from INFINITE
	never_empty: not is_empty
	always_full: full
		-- from ACTIVE
	writable_constraint: writable implies readable
	empty_constraint: is_empty implies (not readable) and (not writable)
		-- from LINEAR
	after_constraint: after implies off
		-- from TRAVERSABLE
	empty_constraint: is_empty implies off

indexing
	library: "[
			EiffelBase: Library of reusable components for Eiffel.
	]"
	status: "[
			Copyright 1986-2001 Interactive Software Engineering (ISE).
			For ISE customers the original versions are an ISE product
			covered by the ISE Eiffel license and support agreements.
	]"
	license: "[
			EiffelBase may now be used by anyone as FREE SOFTWARE to
			develop any product, public-domain or commercial, without
			payment to ISE, under the terms of the ISE Free Eiffel Library
			License (IFELL) at http://eiffel.com/products/base/license.html.
	]"
	source: "[
			Interactive Software Engineering Inc.
			ISE Building
			360 Storke Road, Goleta, CA 93117 USA
			Telephone 805-685-1006, Fax 805-685-6869
			Electronic mail <info@eiffel.com>
			Customer support http://support.eiffel.com
	]"
	info: "[
			For latest info see award-winning pages: http://eiffel.com
	]"

end -- class RANDOM