Author: Dave Gomboc
Date: 01:30:19 01/01/03
Go up one level in this thread
On January 01, 2003 at 02:08:37, Uri Blass wrote: >On January 01, 2003 at 01:01:24, Robert Hyatt wrote: > >>On December 31, 2002 at 20:32:28, Uri Blass wrote: >> >>>On December 31, 2002 at 19:50:43, Robert Hyatt wrote: >>> >>>>On December 31, 2002 at 17:49:52, Uri Blass wrote: >>>> >>>>>From Ed programmer stuff >>>>> >>>>>Killer-One [current ply] 110 >>>>>Killer-One [current ply-2] 108 >>>>>Killer-Two [current ply] 106 >>>>>Killer-Two [current ply-2] 104 >>>>> >>>>>I until today used only >>>>> >>>>>Killer-One [current ply] >>>>>Killer-Two [current ply] >>>>> >>>>>I am interested to know if using 4 killers is a new idea or maybe this idea is >>>>>known to be used by other programs. >>>> >>>>It was known in 1975. Chess 4.0 used this. You can find it mentioned in >>>>the chess 4.7 chapter of "Chess Skill in Man and Machine." >>>> >>>>We did that in Cray Blitz, but we also did more killers, going back to the >>>>root in fact... >>>> >>>> >>>> >>>>> >>>>>I did try part of the idea that Ed suggested without clear results. >>>>> >>>>>I changed the order of moves in movei to >>>>> >>>>>Killer-One [current ply] >>>>>Killer-One [current ply-2] >>>>>Killer-Two [current ply] >>>>> >>>>>instead of >>>>> >>>>>Killer-One [current ply] >>>>>Killer-Two [current ply] >>>>> >>>>>I found that it is better only in part of the cases and have not clear results >>>>>if it is better or worse than previous order but I had a bug in the >>>>>implementation and I checked killer[ply-2] even in cases when ply-2<0. >>>>> >>>>>It is surprising that the program did not crush and even performed better in >>>>>part of the cases. >>>>> >>>>>I still do not use check bound software. >>>>>I asked in a previous discussion about checking bounds but I solved the >>>>>problem that caused me to ask about it and I also read a claim that if a >>>>>varaible is out of bound the program should crush. >>>>> >>>>>I also looked for a software that will help me under visual C++ but after I >>>>>asked to get it for free evaluation and I only got an email that suggest me to >>>>>contact them by fax or telephone I did not respond(I responded by email but my >>>>>email was blocked for some reason and I decided that the subject is probably not >>>>>very important). >>>>> >>>>>I think now that it may be important because a chess program may even play well >>>>>inspite of the fact that it calls killer[-1] so it is possible that I have more >>>>>mistakes like that. >>>>> >>>> >>>>That probably won't hurt a thing. That move probably would not pass your >>>>legality check, so even a garbage move would just waste a tiny bit of time >>>>as you notice it is not legal in the current position. >>> >>>Yes but I can still imagine problems. >>> >>>1)If I am unlucky a garbage move may be legal so it can be counterproductive. >>> >>>2)I thought that garbage may do something worse than giving a random >>>number. >>>I thought that if my program try to look at some place that does not exist the >>>program may crush and not give me a random number or may change another array. >>> >>>I also cared not to have -1 >>> A[x]=1; and not >>>if (x>=0) >>>A[x]=1; >> >>That doesn't hurt a thing. a[-1] is one "thing" before a[0]. If a is an >>integer, a[-1] is simply 4 bytes in front of a[0]... >> >>> >>>If you are right then it means that there are cases when I can save time by >>>doing something like >>> >>>A[x]=1; instead of >>>if (x>=0) >>>A[x]=1; >> >>You can do that just so you _know_ what is in front of A. IE in fortran, >>arrays go from 1 to N, rather than 0 to N-1 as in C. But in Cray Blitz we >>wanted to reference a[i] where i could be 0, 1, ... and all we did was make >>sure that there was a memory word that could safely be zapped, in front of >>a[1]. We did it like this: >> >>common /x/ dummy, a(10) >> >>a(1) thru a(10) are normal array references. a(0) actually stores on top of >>"dummy". >> >> >> >> >>> >>>The point is that if I understand correctly then I understand from your post >>>that a[x]=1 when x=-1 can not change relevant information. >> >>No, it can _definitely_ change something, just not exactly what you think it >>is changing. :) It will change what is in _front_ of the array. In C, the >>only way to know what is in front of the array is to put the array in a >>structure, and then put something right in front of that array declaration >>to declare the "dummy" space needed for a[-1]. Or a[-2] if you want to go >>backward even farther. >> >> >> >>> >>>If I assume that the condition x>=0 happen in most of the cases then it seems >>>clear that A[x]=1 is faster. >> >>Correct. If you know that -1 <= x <= N, then one dummy word in front of the >>array will let you eliminate the test. > >This was only thinking about a theoretical case but I found other things in my >code. > >In a lot of places in my program >I have a condition like > >while (target!=-1&&info[target]==EMPTY) > >In most cases target!=-1 > >I thought that I need to do the && in this order >Do you say that I can change the order without risks? > >Suppose that the loop stops in most of the cases because of the fact that >info[target]=EMPTY. > >Does it going to do my program faster or maybe the compiler can detect these >cases in profile optimazions? > >I thought that even checking the value of info[-1] can give an error or change >some varaible that I do not want. > >Uri Technically, checking the value of info[-1] could even cause your program to crash. But in practice, as long as your program has the ability to access the memory immediately in front of info, it will probably just read the value in that memory location. To be slightly safer, you can declare a padded_info like I suggested elsewhere in this thread. That way even assignments to info[-1] won't cause a problem -- on most architectures, with most compilers. >while (target!=-1&&info[target]==EMPTY) Technically it would be wrong to flip this test around, but in practice you can probably get away with it. Dave
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