Author: Gerd Isenberg
Date: 14:49:41 12/22/05
Go up one level in this thread
On December 22, 2005 at 16:19:58, Zach Wegner wrote:
>Hi Gerd,
>
>Very interesting. I find this line to be particularly elegant:
>
>> l = (h & -m) | (l & m-1);
but also a bit redundant expression
l = h | (l & m-1);
is good enough.
If one likes to scan vectors of bitboards, sse2 comes i mind ;-)
pxor xmm2, xmm2 ; zero
// quad to dword
movdqa xmm1, xmm0
pcmpeqd xmm0, xmm2
psrlq xmm0, 32 ; high == 0 mask
pand xmm0, xmm1 ; low if high == null otherwise zero
psrlq xmm1, 32 ; high
por xmm0, xmm1 ; keeps low if high == 0 otherwise high
// dword to word
movdqa xmm1, xmm0
pcmpeqw xmm0, xmm2
psrld xmm0, 16 ; high == 0 mask
pand xmm0, xmm1 ; low if high == null otherwise zero
psrld xmm1, 16 ; high
por xmm0, xmm1 ; keeps low if high == 0 otherwise high
// word to byte
movdqa xmm1, xmm0
pcmpeqb xmm0, xmm2
psrlw xmm0, 8 ; high == 0 mask
pand xmm0, xmm1 ; low if high == null otherwise zero
psrlw xmm1, 8 ; high
por xmm0, xmm1 ; keeps low if high == 0 otherwise high
// byte to nibble
...
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