Author: Gerd Isenberg
Date: 06:05:11 05/10/05
Go up one level in this thread
>I think I recall that the deBruijn trick was rather fast on the G4 as well,
>but I am not entirely sure. Dieter once posted a slightly more complicated
>version optimized for 32-bit CPUs. It can probably still be found somewhere
>in the archives.
>
I guess Matt Taylor's folding trick:
int bitScanWithReset(BitBoard &bb)
{
static const unsigned int CACHE_ALIGN lsz64_tbl[64] =
{
63,30, 3,32,59,14,11,33,
60,24,50, 9,55,19,21,34,
61,29, 2,53,51,23,41,18,
56,28, 1,43,46,27, 0,35,
62,31,58, 4, 5,49,54, 6,
15,52,12,40, 7,42,45,16,
25,57,48,13,10,39, 8,44,
20,47,38,22,17,37,36,26,
};
BitBoard b = bb ^ (bb - 1);
bb = bb & (bb - 1); // only one further and
unsigned int fold = ((int) b) ^ ((int)(b>>32));
return lsz64_tbl[(fold * 0x78291ACF) >> (32-6)];
}
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