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Subject: Re: unique distance relationship

Author: Vincent Diepeveen

Date: 20:25:25 08/17/02

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On August 17, 2002 at 14:12:03, Gerd Isenberg wrote:

>Hi Vincent,
>
>actually it's faster on my AthlonXP with USE_LOOKUP_XYZ defined!?
>Strange, i also would bet that the one without lookup is faster,
>which only needs 4 instructions by your definition. I don't understand this
>CISC-processors.

Of course the instructions only outperform a table lookup when
the processors L1 and L2 caches are overloaded busy with storing
hashtable entries, doing a big evaluation and other stuff and not having
any time to just put this lookup table in L1 cache.

Only testing the code versus the table is not a good idea obviously.

DIEP doesn't fit in L2 cache at all. I don't need to mention what is
faster for me :)

>Tested in wrong bishop endings and KBN-K (without ETBs), where these inlines are
>used quite often in eval and recognizers. In KBN-K 660KNodes versus 656KNodes.
>But i don't played with optimizations so far (MSC++ minimize size optimization).

see above. this is a typical case where the thing can put many relevant
things in L1 cache.

>May be it's because m_sUDR[a][b] is accessed frequently with quite equal "a" or
>"b" and therefore is mostly already in first level cache - or a lack of
>registers. But the code is definitely shorter with lookup.
>
>#ifdef USE_LOOKUP_XYZ
>inline BOOL sameSquareColor(int a, int b) {return (m_sUDR[a][b]^1) & 1;}
>inline BOOL oppoSquareColor(int a, int b) {return  m_sUDR[a][b] & 1;}
>#else
>inline BOOL sameSquareColor(int a, int b) {return (((a^b)>>3)^(a^b)^1) & 1;}
>inline BOOL oppoSquareColor(int a, int b) {return (((a^b)>>3)^(a^b)) & 1;}
>#endif
>
>(((a^b)>>3)^(a^b)) & 1;
>2 xors because only one (a^b) is necessary
>1 shift
>1 and
>------
>4 instructions

ah great, you found a faster way :)

>see you,
>Gerd



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