Author: Uri Blass
Date: 23:08:37 12/31/02
Go up one level in this thread
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
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