Author: Bas Hamstra
Date: 12:31:05 01/10/03
Go up one level in this thread
Hi Uri,
Personally I use a lookup table for 8 bits at a time (count each row). You can
see a bitboard as an array of 8 unsigned chars.
BB Test = 423434234ui64;
int Count = PopCnt(Test);
inline int PopCnt(BB BitBoard)
{ unsigned char* p = (unsigned char*) BitBoard;
return PopCnt8[p[0]] + PopCnt8[p[1]] ... + PopCnt8[p[7]];
}
You have to create an small precalculated array PopCnt8[256] for this. It is not
the absolute fastest, but also not much slower than that.
Bas.
On January 10, 2003 at 15:16:52, Uri Blass wrote:
>1)How do I use assembler code under C to count the number of 1's in a bitboard?
>I do not know how to copy assembler code from crafty.
>
>I understood from previous post that the relevant code is in crafty but I do not
>know how to copy it correctly with all the #defines in crafty.
>
>I understood that there are some relevant codes(x86.s, vcline.h that I could not
>find and boolean.h
>
>2)I tried a code of dieter and got warning from the compiler(see the bottom of
>this post for that code)
>
>warning C4244: '=' : conversion from 'unsigned __int64 ' to 'unsigned long ',
>possible loss of data
>
>Note that I changed
>int PopCount(unsigned long long a)
>to
>int PopCount(BitBoard a)
>
>I also have in my code
>typedef unsigned __int64 BitBoard;
>
>I also never use the word long in my program except the code that I copied from
>Dieter and I use int for 32 bit numbers.
>
>The warning was about w=
>
>int PopCount(BitBoard a)
>{
> unsigned long w;
> int n = 0;
> w = a&0xffffffffUL;
> if (w)
> do
> {
> n++;
> }
> while ((w &= w-1) != 0);
> w = (a>>32)&0xffffffffUL;
> if (w)
> do
> {
> n++;
> }
> while ((w &= w-1) != 0);
> return n;
>}
>
>Uri
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