Well, nor do most people guard against absolute value failing, even inside their implementation: most people are simply wrong... that said, I also think matter-

Well, nor do most people guard against absolute value failing, even inside their implementation: most people are simply wrong... that said, I also think matter-of-factly "negating" a signed number--rather than asking for the additive inverse of a field element (in which case -128 is the correct answer for -128 as when you later go to add it to another number it will have the correct behavior even if it doesn't look like it makes sense if you pretend it is a number)--is also usually a mistake ;P.