prng-lfsr/test/prng-lfsr-fibonacci16-tests.js

seedable, seeded, pseudo random number generator, prng, linear feedback shift register, fibonnaci, galois, lfsr

var fibonacci16 = require('../').fibonacci16
	, test = require('tape')
	;


/* START common 16bit lfsr tests */
test('fibonacci16 exists', function (assert) {
	assert.ok(!!fibonacci16);
	assert.is('function', typeof fibonacci16);
	assert.end();
});

test('fibonacci16 rejects bad seeds', function (assert) {
	assert.is(fibonacci16(), false, 'mandatory seed!');
	assert.is(fibonacci16('foo'), false);
	assert.is(fibonacci16(function () {}), false);
	assert.is(fibonacci16({}), false);
	assert.is(fibonacci16([]), false);
	assert.is(fibonacci16(65536), false);
	assert.is(fibonacci16(-1), false);
	assert.is(fibonacci16(0), false);
	assert.end();
});

test('fibonacci16 returns a function if seed ok', function (assert) {
	assert.is(typeof fibonacci16(1), 'function');
	assert.is(typeof fibonacci16(2), 'function');
	assert.is(typeof fibonacci16(65535), 'function');
	assert.is(typeof fibonacci16(0xACE1), 'function');
	assert.end();
});

test('fibonacci16 has expected periodicity', function (assert) {

	var seed = 0xACE1
		, g = fibonacci16(seed)
		, remainingIterations = 0xffff // 65535 iterations to return to start
		, lastResult
		;

	while (remainingIterations--) {
		if (seed === lastResult) { assert.ok(false, 'found seed value too early! remainingIterations: ' + remainingIterations) };
		lastResult = g();
	}

	assert.is(lastResult, seed, '0xACE1 -------> 0xACE1 after maximum iterations');

	assert.end();
});

test('fibonacci16 output bit stream', function (assert) {

	var seed = 0xACE1
		, g = fibonacci16(seed)
		, remainingIterations = 0xffff // 65535 iterations to return to start. aka (2^n)-1
		, lastResult

		, bitString = ''

		, maxZeroRun = 					/000000000000000/g		// n - 1
		, impossibleZeroRun = 	/0000000000000000/g 	// n

		, maxOneRun = 					/1111111111111111/g 	// n
		, impossibleOneRun = 		/11111111111111111/g 	// n + 1

		, found
		;

	while (remainingIterations--) {
		lastResult = g();
		bitString += (lastResult >> 15) & 1; // left-most bit is last output bit. NB. different output bit to galois
	}

	assert.is(bitString.length, 0xffff, 'got right number of bits');

	found = maxZeroRun.exec(bitString);
	assert.is(found.length, 1, 'got right number of maximum runs of 0');

	found = impossibleZeroRun.exec(bitString);
	assert.is(found, null, 'got no runs of 0 exceeding n');


	found = maxOneRun.exec(bitString);
	assert.is(found.length, 1, 'got right number of maximum runs of 1');

	found = impossibleOneRun.exec(bitString);
	assert.is(found, null, 'got no runs of 1 exceeding n');


	assert.end();
});
/* END common 16bit lfsr tests */


test('fibonacci16 returns successful next values', function (assert) {

	var g = fibonacci16(0xACE1);

	assert.is(g(), 0x5670, '0xACE1 -> 0x5670');
	assert.is(g(), 0xAB38, '0x5670 -> 0xAB38');

	assert.end();
});