Author: Gerd Isenberg
Date: 12:34:42 10/28/02
Go up one level in this thread
On October 28, 2002 at 15:13:23, Heiner Marxen wrote:
>On October 28, 2002 at 14:06:54, Uri Blass wrote:
>
>>On October 28, 2002 at 13:17:56, Uri Blass wrote:
>>
>><snipped>
>>>My question is if array is the fastest way to do other things like finding if a
>>>rook move is pseudo legal.
>>>
>>>rook move is pseudo legal if the file is the same file or the rank is the same
>>>rank(I can ignore the case when both are the same because this case never happen
>>>and I never expect hash move or killer move when both are the same even in case
>>>of hash collision)
>>
>>After thinking more about the problem it seems that my 2 dimentional array is
>>not the same as checking if the move is pseudo legal because when I get the
>>direction between the squares I get more information than knowing if the move is
>>pseudo legal(the exact direction between the squares(left,right,up,down)
>>and this information is used later.
>>
>>The main question if there is a fast way to calculate the function
>>direction(x,y) when
>>1)direction(x,y)=0 for up direction
>>2)direction(x,y)=1 for down direction
>>3)direction(x,y)=2 for left direction
>>4)direction(x,y)=3 for right direction
>>
>>only a function that is faster than 64*64 array is productive.
>>
>>I am interested in the same question for bishop when direction(x,y) can get
>>4,5,6,7.
>>
>>Uri
>
>Hello Uri,
>
>As you may have seen in the Chest sources, such a direction computation
>can be done with a considerably smaller table, if you start off with
>0x88 coordinate values. The table is indexed with the difference of the
>two 0x88 coordinates, and has size apx 16*16 = 256 entries.
>
>I think, that the biggest problem with such tables is not so much their
>own size, but the cache footprint they leave. That can severely slow down
>the rest of the program.
>
>Whether some computational effort (function/macro) is faster than a table
>lookup, heavily depends on the hardware, e.g. how large is the penalty for
>conditional branches (when decisions are involved), and how smart is
>the compiler to make use of special HW features to avoid conditional code
>for simple conditional constructs (that is possible sometimes).
>
>I will ponder a bit about your exact direction function.
>That could help Chest also, if really good, so I'm motivated :-)
>I've collected some coding tricks over the past years... we'll see what
>I come up with, here.
>
>Cheers,
>Heiner
something like this?
// precondition: a and b share common ray
int dir07 = 6*(rank(a)-rank(b) == file(b)-file(a)) // h1a8
+ 4*(rank(a)-rank(b) == file(a)-file(b)) // a1h8
+ 2*(rank(a) == rank(b)) // common rank
+ (a < b);
Gerd
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