How do I turn a binary string into a float or double?

Question

In this question, Bill The Lizard asks how to display the binary representation of a float or double.

What I\'d like to know is, given a binary string of the appropr

Answer 1

Here's a solution that doesn't use BitConverter and isn't limited by the range of Int64.

static double BinaryStringToDouble(string s)
{
  if(string.IsNullOrEmpty(s))
    throw new ArgumentNullException("s");

  double sign = 1;
  int index = 1;
  if(s[0] == '-')
    sign = -1;
  else if(s[0] != '+')
    index = 0;

  double d = 0;
  for(int i = index; i < s.Length; i++)
  {
    char c = s[i];
    d *= 2;
    if(c == '1')
      d += 1;
    else if(c != '0')
      throw new FormatException();
  }

  return sign * d;
}

This version supports binary strings that represent values between to Double.MinValue and Double.MaxValue, or 1023 significant binary digits. It overflows to Double.PositiveInfinity or Double.NegativeInfinity.

@LukeH's answer only supports binary strings that represent values between to Int64.MinValue and Int64.MaxValue, or 63 significant binary digits.

Why you'd have a need for a binary string that is more than 63 digits in length is up for discussion.

If you don't want to allow a leading sign character, you can use this simpler version that only returns positive values.

static double BinaryStringToDouble(string s)
{
  if(string.IsNullOrEmpty(s))
    throw new ArgumentNullException("s");

  double d = 0;
  foreach(var c in s)
  {
    d *= 2;
    if(c == '1')
      d += 1;
    else if(c != '0')
      throw new FormatException();
  }

  return d;
}