Why computers have two zeros: +0 and -0

Here’s a strange detail of floating point arithmetic: computers have two versions of 0: positive zero and negative zero. Most of the time the distinction between +0 and -0 doesn’t matter, once in a while signed versions of zero come in handy. If a positive quantity underflows to zero, it becomes +0. And if a negative quantity underflows to zero, it becomes -0. You could think of +0 (respectively,