ulp/lib/index.js

Math.nextAfter, Math.nextDown, Math.nextUp, Math.ulp in javascript (from https://gist.github.com/Yaffle/4654250)

"use strict"

var EPSILON = Math.pow(2, -52)
var MAX_VALUE = Number.MAX_VALUE
var MIN_VALUE = Math.pow(2, -1022)

function nextUp(x) {
  if (x !== x) return x
  if (x === -1 / 0) return -MAX_VALUE
  if (x === 1 / 0) return +1 / 0
  if (x === MAX_VALUE) return +1 / 0
  var y = x * (x < 0 ? 1 - EPSILON / 2 : 1 + EPSILON)
  if (y === x) y = MIN_VALUE * EPSILON > 0 ? x + MIN_VALUE * EPSILON : x + MIN_VALUE
  if (y === +1 / 0) y = +MAX_VALUE
  var b = x + (y - x) / 2
  if (x < b && b < y) y = b
  var c = (y + x) / 2
  if (x < c && c < y) y = c
  return y === 0 ? -0 : y
}

function nextDown(x) {
  return -nextUp(-x)
}

function ulp(x) {
  return x < 0 ? nextUp(x) - x : x - (-nextUp(-x))
}

exports.nextUp = nextUp
exports.nextDown = nextDown
exports.ulp = ulp

exports.monkeypatch = function monkeypatch() {
  Math.nextUp = nextUp
  Math.nextDown = nextDown
  Math.ulp = ulp
}