Hi,
> But the max. error in sinh/cosh/atanh is less than 2 ULP, with some math
> libraries. It could be < 1 ULP, in theory, so sinh(atanh(x)) less than
> 2 ULP even.
You can't add ULP errors in general - a tiny difference in the input can
make a huge difference in the result if the derivative is > 1.
Even with perfect implementations of 0.5000001ULP on easy functions with
no large derivatives you could get a 2ULP total error if the perfectly rounded
and actual result end up rounding in different directions in the 2nd function...
So you have to measure ULP error since it is quite counter intuitive.
> And signed zeroes. Yeah. I think it would have to be
> flag_unsafe_math_optimizations + some more.
Indeed.
Wilco
