Author: Tony Werten
Date: 00:27:47 04/24/01
Go up one level in this thread
On April 23, 2001 at 19:30:20, Alex Boby wrote:
>
>I used to have this:
>
>------------
>void parseBitboard (int from, struct MoveList *ml, bitboard attack)
> {
> int i;
>
> for (i=0; i<64; i++)
> {
> if (attack&mask[i])
> [add move to list]
> }
> }
>------------
>and got this in the profile:
>7301.351 3.9 37127.739 19.6 538488 _parseBitboard (pierre.obj)
>
>and then, figuring I would get a significant speed increase, I switched to this:
As Landon pointed out in his post, chance it to a complete assembly function.
I think (might be wrong ) C++ and Delphi have the same beheavior in this. By
starting a function in a high language and then using asm insisde it, you get a
lot of everhead (ie if asm is not the first word in the function ), plus
optimization goes nuts.
The instruction "int index" makes the compiler create a stack, a result variable
(instead of using registers to return the value ) and more things you don't
want. This way it's virtually imposible to improve the speed.
cheers,
Tony
>
>-----------------
>int findBitIndex(bitboard data)
> {
> int index;
>
> __asm
> {
> bsr edx, dword ptr data+4
> mov eax, 32
> jnz s1
> bsr edx, dword ptr data
> mov eax, 0
> jnz s1
> mov edx, -1
> s1: add edx, eax
> mov index, edx
> }
>
> return index;
> }
>
>void parseBitboard (int from, struct MoveList *ml, bitboard attack)
> {
> int index;
>
> while ((index = findBitIndex(attack))!=-1)
> {
> [add move to list]
> attack -= mask[index];
> }
> }
>-------------
>and then got this in the profile:
> 6763.331 4.4 32424.707 21.1 530420 _parseBitboard (pierre.obj)
> 1313.554 0.9 1313.554 0.9 3523746 _findBitIndex (pierre.obj)
>
>with about a 10% drop in nodes/sec.
>
>I thought that BSF & BSR were supposed to be fast! What am I doing wrong?
>This is on an Intel P3/500 w/ win2k.
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