prng-lfsr/example/rbgStream.js

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

// KLUDGEZONE - temporary code below.
// Offer a rudimentary RBG (Random Bit Generator) for piping the relevant outputBit to dieharder and the like...
// NB. no unit tests as yet, expect to move/replace this api in future.
// TODO consider offering the full PRNG output as:
// 1) a numeric stream - 0xACE1
// 2) a hex digest stream 'ACE1'
// 3) a complete bit stream 0110010101010010100...
// ...etc. etc. etc...
// If so, should NOT live here anyway! ;)

//	See example/prng-lfsr-stream.js for usage
var prngLFSR = require('../')
	, fibonacci16 = prngLFSR.fibonacci16
	, galois16 = prngLFSR.galois16
	, kludgeyStream = (function () {

		var util = require('util')
			, stream = require('stream')
			, RBGStream = function RBGStreamConstructor() {
					this.readable = true;
					this.writable = true;
				}
			;

		util.inherits(RBGStream, stream);

		RBGStream.prototype.write = function RBGStreamProtoWrite(data, outputBitOffsetFromLSB) {
			// select the relevant outputBit
			this.emit('data', new Buffer((data >> outputBitOffsetFromLSB) & 1, 'binary'));
			// this.emit('data', new Buffer(data, 'binary'));
		};

		RBGStream.prototype.end = function RBGStreamProtoEnd() {
			this.emit('end');
		};


		//	kludgey augmenting of lfsr types with outputBit offset, this IS temporary, yeh!
		//	|0110011010010101|
		//	|            3<--|
		fibonacci16.outputBitOffset = 15;
		galois16.outputBitOffset = 0;

		return function (prngType, seed, destination) {

			var wrapper
				, prng
				, rbg
				// saves typing fibonnaci wrong... ahem. (yes, i will remove it and inject prng instead)
				, validTypes = {
					'FIB16': fibonacci16,
					'GAL16': galois16
				}

			// rudimentary guarding
			if ( !prngType
				|| !validTypes[prngType]
				|| !(prng = validTypes[prngType](seed))
				|| !destination) return false;

			rbg = new RBGStream();
			rbg.pipe(destination);

			wrapper = function wrapperNext() {
				var prngState = prng();
				rbg.write(prngState, prng.outputBitOffset);
				return prngState;
			};

			// allow instance.end();
			wrapper.end = function () {
				rbg.end();
			};

			// whenever wrapper is invoked the next state will be piped to destination
			return wrapper;
		};
	}());
	;

module.exports = kludgeyStream;