JS Custom Hashing function with benchmarks

.gitignore

*.txt

README.md

JavaScript Custom Hashing Function

A custom string hashing function written in JavaScript.

Benchmarks

Version	Words	Runtime (Seconds)	Collisions	%
1	7,849,570	6.169	1,380	0.019460504060899532
2	7,849,570	6.853	98	0.0012484760311711341

Explanation

I continued trying variations of the available operators in JS until I got the value as low as possible while not sacrificing too much runtime.

collision-tester.js

// This is a basic collision tester that can make checking for collisions a little easier! To use it, enter each key (in this case, a word) you want to check into the test-words.txt file, with each key in a different line. Then, run collision-tester.js, and the program will tell you how many collisions it detected between the word you've inserted.

var oldlog = console.log
console.log = function() {}

const fs = require('fs');
const usr = require("./index.js");

console.log = oldlog

function areSetsEqual(a, b) {
	if (a.size !== b.size) return false;
	for (const c of a) if (!b.has(c)) return false;
	return true;
}

function testCollisions(filepath){
	fs.readFile(filepath, 'utf8' , (err, data) => {
		if (err) return console.error(err);


		const words = data.split('\n');

		const start = Date.now();
		const hashes = new Set(words.map(usr.my_hash));
		const end = Date.now();

		const collisions = words.length - hashes.size;
		console.log("\t" + filepath + " results")
		console.log("Total words: " + words.length);
		console.log("Number of Collisions Detected: " + collisions);
		console.log("Collision %: " + collisions / words.length * 100)
		console.log("Runtime: " + (end - start))

		if (!areSetsEqual(hashes, new Set(words.map(usr.my_hash)))) {
			console.error('Hash function is NOT stable!')
		}
	});
}

testCollisions('test-words.txt');
testCollisions('generated-words.txt');

generator.js

const fs = require('fs');

const DURATION = 10;

const values = new Set();

const started = Date.now();
let characters = 1;
for(let remaining; remaining = DURATION * 1000 - (Date.now() - started), remaining > 0; characters++){
	for (let _ = 0; _ < 100; _++){
		values.add(Math.random().toString(36).replace(/[^a-z]+/g, '').substr(0, characters))
	}

	process.stdout.write((remaining / 1000).toFixed(1) + '     \r');
}
console.log(`Generated ${characters * 100} strings!`);

console.log('Writing to file...')
fs.writeFileSync('./generated-words.txt', Array.from(values).sort().join('\n'));

index.js

// This function, my_hash(), is where you should write your hash function. Like last module, input is a string, and the hash function should return an integer.

/**
 * @param {string} input
 * @returns {string}
 */
function my_hash(input){
	let hash = input.length;
	for (let i = 0; i < input.length; i++){
		hash += (hash ^ input.charCodeAt(i)) * (hash << 6)
	}
	return hash * input.length;
}

// An example test case!
console.log(my_hash("boblover1234"));

// This is for the collision tester, and can be ignored (it passes your function onto the collision tester to test)

module.exports = {my_hash};