Author: Uri Blass
Date: 08:13:05 08/23/03
Go up one level in this thread
On August 23, 2003 at 10:39:53, Gerd Isenberg wrote:
>On August 23, 2003 at 07:07:25, Uri Blass wrote:
><snip>
>
>>>>for (k=0;k<weight[i];k++)
>>>>f(power[i][k]);
>>>>
>>>>Uri
>>>
>>>I see, but instead of saving "i" (may be only a register/register mov), you have
>>>an additional [256][8] table. Anyway, if this is a hotspot and function "f" is
>>>cheap you may consider loop unrolling, even with inlined "f".
>>
>>I do not know
>>practically I do not have f as a function but as a list of 3 commands so my
>>profiler does not tell me exactly how much time I use for it.
>>
>>I only know that the lines are inside functions that take significant time
>>(near 20% of all the time that the program runs).
>>
>
>Ok, that's worth to optimize.
>
>
>>
>> If the order of
>>>"k" doesn't matter, in that way:
>>>
>>>switch (weight[i])
>>>{
>>>case 8: f(power[i][7]);
>>>case 7: f(power[i][6]);
>>>case 6: f(power[i][5]);
>>>case 5: f(power[i][4]);
>>>case 4: f(power[i][3]);
>>>case 3: f(power[i][2]);
>>>case 2: f(power[i][1]);
>>>case 1: f(power[i][0]);
>>>case 0: break;
>>>}
>>>
>>>with MSC you may add a default case with assume(0).
>>>
>>>Gerd
>>
>>Thanks
>>I may try it.
>>
>>I may save case 0 and case 1 and more cases when I know that they can never
>>happen
>>
>>the number of directions that king can go in an empty board is 8,5 or 3 and
>>there are no more possibilities.
>>
>>The number of directions that knight can go in an empty board(calculated
>>manually) is only 2,3,4,6,8 if I have no mistake.
>>
>>Uri
>
>That only matters if the switch is implemeted with a "if else if else" chain,
>but optimizing compiler like MSVC will use a jmp-table here.
>
>I wonder whether your algorithm's runtime is dependend on the numbers of
>directions at all. If you have all 8 directions, is there no way to combine the
>8 steps partially in some way, e.g. by combining some ors?
I do not know
The main problem is that in that case I update information about different 8
squares.
If I move a white piece from e2 or to e2 then I update information for every
square in the board that a queen at e2 can go when I stop some direction only
after seeing a square that is not empty.
Maybe the big numbers of updates is the main reason that the functions are slow
so the fact that these functions take significant time does not mean that I can
earn a lot by optimizations.
In the same functions in part of the cases I check only squares that a king can
go or every square that a knight can go but there are cases when I update
information for every square that a queen can go and if I am not lucky it may be
a lot of updates of an array.
Uri
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