code: function sign(x) {
    // eslint-disable-next-line no-self-compare
    return typeof x === "number" ? x ? x < 0 ? -1 : 1 : x === x ? x : NaN : NaN;
  }
docs: Polynomial.js
  
  @module Polynomial
  @copyright 2002-2019 Kevin Lindsey<br>
  -<br>
  Contribution {@link http://github.com/Quazistax/kld-polynomial}<br>
  2015 Robert Benko (Quazistax) <quazistax@gmail.com><br>
  MIT license
   
  Sign of a number (+1, -1, +0, -0).
  
  @param {number} x
  @returns {number}