But am I correct in thinking that is at worst a 0.5 ulp error in this case? The lesser term in double-double can't be more than 0.5 ulp of the greater term and

But am I correct in thinking that is at worst a 0.5 ulp error in this case? The lesser term in double-double can't be more than 0.5 ulp of the greater term and sensitivity of both sine and cosine to an error in the input will not be more than 1. Also, in case of confusion, I was specifically commenting on the function over the [-pi/4, pi/4] domain in https://github.com/ifduyue/musl/blob/master/src/math/__cos.c https://github.com/ifduyue/musl/blob/master/src/math/__cos.c , which the comment in https://news.ycombinator.com/item?id=30846546 https://news.ycombinator.com/item?id=30846546 was presumably about.