pow-approx-pow10.js

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if (typeof fdlibm === "undefined") {

  var fdlibm = SpecialPowers.Cu.getJSTestingFunctions().fdlibm;

const f64 = new Float64Array(1);

const ui64 = new BigUint64Array(f64.buffer);

function toBits(n) {

  f64[0] = n;

  return ui64[0];

function errorInULP(actual, expected) {

  // Handle NaN and +0/-0.

  if (Object.is(actual, expected)) {

    return 0;

  let x = toBits(actual);

  let y = toBits(expected);

  return x <= y ? Number(y - x) : Number(x - y);

const maxExponent = Math.trunc(Math.log10(Number.MAX_VALUE));

const minExponent = Math.trunc(Math.log10(Number.MIN_VALUE));

assertEq(Math.pow(10, maxExponent + 1), Infinity);

assertEq(Math.pow(10, minExponent - 1), 0);

// Ensure the error is less than 2 ULP when compared to fdlibm.

for (let i = minExponent; i <= maxExponent; ++i) {

  let actual = Math.pow(10, i);

  let expected = fdlibm.pow(10, i);

  let error = errorInULP(actual, expected);

  assertEq(error < 2, true,

           `${10} ** ${i}: ${actual} (${toBits(actual).toString(16)}) != ${expected} (${toBits(expected).toString(16)})`);

// Ensure the error is less than 2 ULP when compared to parsed string |1ep|.

for (let i = minExponent; i <= maxExponent; ++i) {

  let actual = Math.pow(10, i);

  let expected = Number("1e" + i);

  let error = errorInULP(actual, expected);

  assertEq(error < 2, true,

           `${10} ** ${i}: ${actual} (${toBits(actual).toString(16)}) != ${expected} (${toBits(expected).toString(16)})`);

if (typeof reportCompare === "function")

  reportCompare(true, true);