Author: Uri Blass
Date: 09:44:07 01/06/04
Go up one level in this thread
On January 06, 2004 at 10:56:00, martin fierz wrote:
>On January 06, 2004 at 09:40:33, Robert Hyatt wrote:
>
>>Maybe there is some confusion here. There is _no_ cost for "allocating"
>>local variables in a function. And I _do_ mean _NO_. These values are
>>simply "on the stack" and when the function is entered, the stack pointer has
>>some constant subtracted from it to leave a "hole" that is used to hold local
>>function variables. no malloc() or anything like that is done by modern
>>compilers, hence zero cost.
>
>hi bob,
>
>is this really true? i used to have a HUGE structure describing a move in the
>first version of my chess program (don't ask, please...). in my negamax function
>i had this
>
>int negamax(int alpha, int beta, int depth)
> {
> MOVE movelist[MAXMOVES];
> ...other variables...
>
> ...typical negamax code...
>
> }
>
>i saw clear speed differences depending on the value i used for MAXMOVES - and
>in my tests, i made sure that using 100 would never overflow in the positions i
>was searching, then i set it to e.g. 200 and the program would get a few %
>slower, although these additional 100 array elements were never used.
>
>how can this be explained? i'm not memsetting the array to 0 or anything.
>
>like uri, i thought the program was allocating memory every time it entered the
>function, and that that was taking time. i ended up making my MOVE variable much
>smaller - although it's still much larger than crafty's :-)
>
>i thought perhaps i should allocate the movelist beforehand as a global, like
>this:
>
>MOVE *movelist[MAX_SEARCH_DEPTH]
>for(i=0;i<MAX_SEARCH_DEPTH;i++)
> movelist[i] = malloc(sizeof(MOVE)*MAXMOVES)
My move list is in a global varaible like tscp
gen_t gen_dat[GEN_STACK];
The list include legal moves of all plies.
For example if I search the line 1.e4 e5 the list includes legal move of white
in the initial position,legal moves of black after 1.e4 and legal moves of white
after 1.e4 e5
GEN_STACK is 30,000 that is clearly more than enough but I remember from
exeperience that changing the size of the global array did not make big
difference.
I do not use pointers when I do not need them and I see no reason to use malloc
for the move list.
Uri
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.