Author: martin fierz
Date: 13:15:01 04/11/04
Go up one level in this thread
On April 11, 2004 at 16:02:56, Robert Hyatt wrote:
>On April 10, 2004 at 14:17:08, martin fierz wrote:
>
>>On April 10, 2004 at 13:36:50, Anthony Cozzie wrote:
>>
>>>On April 10, 2004 at 12:51:28, martin fierz wrote:
>>>
>>>>hi ed,
>>>>
>>>>you posted the stuff below a day or two ago, and i have a question about it:
>>>>
>>>>you suggest creating a "translation table" to get an unbroken and continuous
>>>>string of characters and then use this in a switch statement. if i understand
>>>>this right, i'd have to make a rather large first table which does something
>>>>like
>>>>
>>>>material-signature = function(pieces); somewhere in the 0...~4000 range (as far
>>>>as i can see, you need to be able to represent any combination of 1 vs 1 or
>>>>better 2 vs 2 pieces)
>>>>
>>>>X=conversiontable[material-signature] ~ somewhere in the 0...20 range for all
>>>>special cases you want to consider.
>>>>
>>>>then you do switch(X) - now how does the compiler know that the conversiontable
>>>>values are in a single range?? i don't understand how it can possibly know this
>>>>:-(
>>>>
>>>>cheers
>>>> martin
>>>
>>>By default it simply bounds checks.
>>>
>>>e.g.:
>>>
>>>if(value < 0) jmp default;
>>>if(value > X) jmp default;
>>>jmp[table[value]];
>>
>>i still don't understand: how does the compiler know what values table[value]
>>can take? in your example, the compiler knows from somewhere that these values
>>are in the range 0...X. how?
>>
>>cheers
>> martin
>
>You tell it. :)
>
>case 0:
>case 1:
>case etc:
>default:
>
>:)
stupid me :-)
cheers
martin
>
>
>>
>>>Or, you could always do the bounds check yourself (I think the compiler
>>>is smart about this):
>>>
>>>switch(a & 1023)
>>>{
>>>
>>>}
>>>
>>>Lastly, I believe there is a #pragma for most compilers that removes the bounds
>>>check.
>>>
>>>anthony
>>>
>>>>*******************************************************************************
>>>>I think I misread, I thought one of your worry was all the time-consuming
>>>>compares and jumps to go to the relevant parts of eval depending of the material
>>>>on the board. If so, create a 2-dimensional translation table that converts the
>>>>present material to an unbroken and continuous string of characters
>>>>(0,1,2,3,4,5.....) and then use the result with switch-case.
>>>>
>>>>I have such an endgame table with over 30 entries (KPK, KRK, KBNK, KQKR, KNKPP,
>>>>KBKPPP, KRPKR etc.) and instead of doing 30 expensive compares I just have to do
>>>>2 initialization instructions, get the value of the translation table and then
>>>>the switch-case will move me with just one assembler instruction to the right
>>>>place (label). Imagine the speed gain.
>>>>
>>>> switch (val) { case 0 : goto KPK;
>>>> case 1 : goto KRK;
>>>> case 2 : goto KNBK;
>>>> case 3 : goto KQKR;
>>>> ...................
>>>> case 99 : goto whatever;
>>>> }
>>>>
>>>>Again, the compiler will translate this to just *one* instruction, even if you
>>>>have 200 entries and thus save 200 compares.
>>>>
>>>>Ed
>>>>*****************************************************************************
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