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Micro-optimize pop_lsb() for 64bit case
On Intel, perhaps due to 'lea' instruction this way of zeroing the lsb of *b seems faster than a shift+negate. On perft (where any speed difference is magnified) I got a 6% speed up on my Intel i5 64bit. Suggested by Hongzhi Cheng. No functional change.
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Very nice!
Here is another issue that might need your attention, which is quite similar to one of those issues I pointed out before.
In function connected_moves(), Stockfish has
It is possible that square f2 will block an x-ray attack from p1, so it would be correct if we modify the above code as:
Thanks a lot
Hongzhi
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