[tmyklebu]

If you're just looking for hard-to-round inputs, you can also enumerate the double precision space completely with some cleverness and modest patience.

Elkies [0] computes a piecewise linear approximation to his (number-theoretic) function of interest and does a lattice reduction on each piece to filter out the vast majority of the space. The same approach, works almost everywhere on all of the transcendental functions I've tried, and I believe the CRlibm group uses it.

[0] https://arxiv.org/pdf/math/0005139.pdf

[bsder]

Oooh, that's an interesting take.