Author: Russell Reagan
Date: 19:00:16 01/17/03
Go up one level in this thread
On January 17, 2003 at 20:28:03, David Rasmussen wrote:
>I profiled my code and found (not very surprisingly) that
>
>INLINE BitBoard Mask(Square square) { return mask[square]; }
>
>was a hotspot.
>
>I tried to change it to
>
>INLINE BitBoard Mask(Square square) { return BitBoard(1) << square; }
>
>I've tried that many times before, and this time too, the latter was slower. But
>why? I mean, the latter is one instruction on x86 or something like that, and
>square is probably in a register anyway. I would think that it would be faster
>than a table lookup which accesses slow memory.
>
>How come?
Well, neither of those are one instruction unless you are using 32-bit
bitboards, or you are writing a checkers program, or you have a 64-bit computer.
The table lookup shouldn't have any "slow memory accesses", but rather in the
cache. I would think that the table lookup in the cache would be faster than a
64-bit shift.
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