> There would be two ways to represent 0, as +0 and -0.
IEEE 754 floating point actually has this (due to having a dedicated sign bit). I think most code doesn't care (IIRC they are defined as equal for comparison purposes even though the bits are different in memory), but apparently it's sometimes handy to have for some functions that have a discontinuity at zero or otherwise need to preserve the sign through a multiplication by zero.
By the time you have implemented enough silicon for floating point addition and multiplication, the amount of extra transistors you would need to special case the compare operator's zero case is realtivily tiny.
The same can not be said for an interger alu (especially one without hardware multipliers or even arbitrary bit shifts), where twos complement representation can save a much larger percentage of silicon.
Because of this, javascript has a +0 and a -0. They make a fun trivia question because there are very few ways to distinguish them since most of the ways of checking equality (even ===) will report that they are equal.
In fact, I only know two ways to distinguish them: divide something by them, and you get positive infinity for +0 and negative infinity for -0, or you can use Object.is(-0, 0) which will return false.
You sometimes want to be able to distinguish positive underflow from negative underflow. In the same way you sometimes want to distinguish positive overflow (infinity) from negative overflow (minus infinity).
IEEE 754 floating point actually has this (due to having a dedicated sign bit). I think most code doesn't care (IIRC they are defined as equal for comparison purposes even though the bits are different in memory), but apparently it's sometimes handy to have for some functions that have a discontinuity at zero or otherwise need to preserve the sign through a multiplication by zero.