Extracting the exponent and mantissa of a Javascript Number

Question

Is there a reasonably fast way to extract the exponent and mantissa from a Number in Javascript?

AFAIK there\'s no way to get at the bits behind a Number in Javascri

Answer 1

While I liked the accepted solution, using it to work on arbitrary base re-introduced all of the errors caused by Math.log and Math.pow. Here is a small implementation for any base: x = mantisse * b^exponent

function numberParts(x, b) {
  var exp = 0
  var sgn = 0
  if (x === 0) return { sign: 0, mantissa: 0, exponent: 0 }
  if (x<0) sgn=1, x=-x
  while (x>b) x/=b, exp++
  while (x<1) x*=b, exp--
  return { sign: sgn, mantissa: x, exponent: exp }
}

The NaN and Infinite cases can easily be added. If the distinction between +0 and -0 is important:

if (1/x === Infinity) return { sign: 0, mantissa: 0, exponent: 0 }
if (1/x === -Infinity) return { sign: 1, mantissa: 0, exponent: 0 }

Answer 2

What about following to get the exponent?:

let exp = String(number.toExponential());
exp = Number(exp.substr(exp.lastIndexOf('e')+1));

1000 will result in exp = 3