HGCD_REDUCE_THRESHOLD is almost always 996, please see <http://gmplib.org/devel/HGCD_REDUCE_THRESHOLD.html>. I tried adding param.max_size = 10000 to tune_hgcd_reduce, and on shell.gmplib.org I now get 3681. Measurements become very slow, one might want to set a coarser step factor too. -- Torbjörn