Nullmove bugs

[bob]

Is the nodetype != NodeTypePV condition a requirement of null move pruning? I ask because when I added that restriction, my search became painfully slow.

Shouldn't matter that much. There aren't that many PV nodes, but if the null-move fails high (which might get backed up to the root and trigger a research with a larger aspiration window) it might be costly, especially if the fail-high is undeserved. I guess it will depend a lot on how you handle your aspiration window and other minor details.

EDIT: I just tried with Jazz; allowing null-move in the PV adds about 2% to the node count for a fixed depth search (NPS is constant, so the time to depth increases by a similar 2%). Seems it should just be a speed optimisation to not do it in PV nodes.

That is my finding as well...