My answer to "implement fabs(), incorrectly". Seven and one third internet points to anyone who can say why it's incorrect, without looking up the spec. Hint: It's implementation defined. (Using C99 semantics because that's the only one I know reasonably well. :)https://twitter.com/oe1cxw/status/1144274172253822976 …
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I don't see the problem with this one. Either the compiler doesn't promise IEEE 754 and -x doesn't even need to be exact, or it does but (see other discussion) the sign bit of NaN is meaningless (and even getting the correct payload is a stretch tbh). Is this about 0. and -0.?
Yes, it's about negative zero. fmax(+0.0, -0.0) is allowed to return -0.0, and fabs(-0.0) is required to return +0.0.