IEEE-754 Floating Point in Javascript

ieee-754-floating-point.js

const pad = (str, n, a=0) => Array.from({length:n-str.length}).map(_ => a).join('') + str;
const nextPowerOf2 = (n) => Math.pow(2, Math.round(Math.max(n,0)).toString(2).length);

const getPowerOfTwoWindow = n => {
    const next = nextPowerOf2(n);
    return [next/2, next];
};

const floatToBinary = (n) => {
  const sign = n > 0 ? 0 : 1;
  const window = getPowerOfTwoWindow(n);
  const windowStartAsPowersOfTwo = Math.log(window[0])/Math.log(2);
  const exponent = 127 + windowStartAsPowersOfTwo;
  const windowSize = window[1]-window[0];
  const m = (N - windowSize)/windowSize;
  const mantissa = Math.ceil(Math.pow(2, 23) * m);

  const binary_sign = pad(sign.toString(2),1);
  const binary_exponent = pad(exponent.toString(2),1);
  const binary_mantissa = pad(mantissa.toString(2), 23);

  return `${binary_sign}${binary_exponent}${binary_mantissa}`
};



const binaryToFloat = binary => {
  const sign = binary.substring(0,1);
  const exponent = binary.substring(1,9);
  const mantissa = binary.substring(9,32);

  const S = sign;
  const E = parseInt(exponent,2);
  const M = parseInt(mantissa, 2) /Math.pow(2,23);

  // (-1)^S * (1 + M) * 2^(E-127)
  return Math.pow(-1,S) * (1 + M) * Math.pow(2, E-127)
};

const N = 3.20;
const binary = floatToBinary(N);
const float = binaryToFloat(binary);

console.log('44, N -—>', N);
console.log('45, binary -—>', binary);
console.log('46, float -—>', float);