Hash modulo

hash-modulo.js

// from https://www.npmjs.com/package/sha1
var sha1 = require("sha1")

// compute (sha1) hash modulo
function hash_modulo(str, modulo) {
  // ignore case of input
  str = str.toUpperCase();
  // compute sha1 of input
  let h = sha1(str);
  // use only the 8 last bytes (4 last hex chars) of the sha1
  h = h.substr(-4);
  // append '0x', parse as int, and compute modulo
  return (+('0x'+h)) % modulo;
}

// detect collisions
const all = new Set();
let col = 0;

// print test 
function t(s) {
  var h = hash_modulo(s, 40);
  if (all.has(h)) { col++; }
  all.add(h);
  console.log(s + ' ' + h);
}

// test for various input
t('company');
t('market');
t('Investor');
for (let i='a'.charCodeAt(0); i <= 'z'.charCodeAt(0); ++i) {
  t(String.fromCharCode(i));
}

console.log('collisions: ' + col);