> But that means you really need five variants of the sin function and you need to dynamically dispatch between them based on the current rounding mode. That w

> But that means you really need five variants of the sin function and you need to dynamically dispatch between them based on the current rounding mode. That would be one way to achieve the behavior you describe, but it is certainly not the only way, nor is it the best. You could, for example, do a computation that produces a result rounded to odd with a few extra bits (independent of the prevailing rounding mode), then rounds that result to the destination precision using the prevailing mode. This assumes that you really want correct-rounded transcendentals anyway, which at present are sufficiently slow that you might as well dispatch based on rounding mode (despite the herculean efforts of the CRLibm crew). If faithful rounding is all that is required, even simpler methods exist that are extremely performant.