Author: Leen Ammeraal
Date: 07:08:31 06/26/01
Go up one level in this thread
On June 26, 2001 at 08:48:19, Uri Blass wrote:
>This question is important for my move generator
>
>dirnow is a 16 bit non negative integer and I want to translate it to an array
>that include the place of it's digit.
>example:
>Suppose dirnow=131=2^7+2^1+2^0
>I want to get from dirnow the following information:
> directionsq[0]=7
> directionsq[1]=1
> directionsq[2]=0
>
>In most of the cases dirnow is a number with a lot of 0's and only few 1's.
>
>How to do it in the fastest way?
>
>one possible way is to use big arrays
>a[65536][16]
>weight[65536];
>
>This arrays should be calculated only one time and I get
>
>a[131][0]=7
>a[131][1]=1
>a[131][2]=0
>weight[131]=3
>
>in this case I only need to do
>i=0;
>while (i<weight[dirnow])
> directionsq[i]==a[dirnow][i];
>
>The number of commands seem to be very small but I am afraid that big arrays may
>do the program slower.
>
>Another way is to use the following small arrays
>a[256][8]
>weight[256]
>
>In this case I need to do something like
>i=0;
>While (i<weight[dirnow&(1<<16-1<<8)>>8])
> directionsq[i]=8+a[(dirnow&(1<<16-1<<8))>>8][i];
>j=0;
>While (j<weight[dirnow&255])
> directionsq[i+j]=a[(dirnow&255)][j];
>
>I decided to write 1<<16-1<<8 to do it more simple to understand and I think to
>use an exact number in my move generator.
>
>Uri
Is this what you mean? And would it be
fast enough?
int n = 0;
for (int i=15; i>=0; --i)
if (dirnow & (1 << i))
directions[n++] = i;
Leen Ammeraal
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