see

[flok]

I think I understand it
It's just that I find it difficult to get it right.
But the current version does all 3 cases right! (queen/knight/knight as attacker giving -550, 100 and 100)

Thank you all.


(more testcases welcome but don't feel obliged

[petero2]

(more testcases welcome but don't feel obliged :-)

I have some test cases I used when implementing SEE in cuckoochess:

https://github.com/peterosterlund2/droi ... .java#L276

In complicated cases the SEE value may depend on your implementation though. This can happen when there are multiple X-ray threats to the target square.

[Steve Maughan]

You may find this blog post helpful:

https://www.chessprogramming.net/static ... -in-chess/

Steve

[Maarten Claessens]

What about the see-value of fxe5 in this position:
[d]8/2q2k2/4rb2/4pR2/5P2/3N4/Q7/4K3 w - - 0 1

[flok]

I would say +975.

(for pawn 100, knight 325, bishop 325, rook 500, queen 975, king 10000)

[elcabesa]

Why?
My see doesn't take in account checks and maybe pinned pieces.(I have to check the source).
I think the result depend on how you calculate it.

[Maarten Claessens]

WaDuuttie calculates +100 (with pin detection: PxP, not followed by QxP because of NxQ) or 0 (without pin detection: PxP BxP NxB RxN RxR QxR).

[AlvaroBegue]

I would say +975.

(for pawn 100, knight 325, bishop 325, rook 500, queen 975, king 10000)

That makes no sense. A [non-promoting] capture can't have an SEE value higher than the value of the captured piece, because the opponent could just stand pat after it.

[flok]

(I'll respond later to this; no access to my development machine (my laptop at home) right now)

[flok]

Hi Steve,

I followed your post -leaving out the early bailouts for now.
That works in some cases but not all. E.g. [d]8/2q2k2/4rb2/4pR2/5P2/3N4/Q7/4K3 w - - 0 1[/d] gives 1200.
It's probably due to that threshold. My question now is: what is the value of the threshold compared to the piece values?

Code: Select all

// xy are of the victim
int Scene::getSEE(const int x, const int y, const ChessPiece *const attacker) const
{
	const ChessPiece *const victim = b.getAt(x, y);

	const PlayerColor c = attacker -> getColor();

	// bit 0...15: if set, then a white piece can walk over and/or attack this field, 16...31 black
	const uint32_t bits = ss.back().tcs.cells[y][x];

	int see_val = victim -> getEvalVal();
	int trophy_val = attacker -> getEvalVal();

	PlayerColor sc = opponentColor(c);
	int so[] = { 0, 16 }; // where to start to search in the bit pattern. so[0] is for white
	constexpr int soe[] = { 16, 32 }; // where to stop searching. soe[0] is for white

	for&#40;; so&#91;sc&#93; < soe&#91;sc&#93;;) &#123;
		// find a 1 bit
		while&#40;&#40;bits & &#40;1 << so&#91;sc&#93;)) == 0&#41; &#123;
			// if end of pattern, stop searching
			if (++so&#91;sc&#93; == soe&#91;sc&#93;)
				break;
		&#125;

		if &#40;so&#91;sc&#93; >= soe&#91;sc&#93;)
			break;

		if &#40;sc == c&#41;
			see_val += trophy_val;
		else
			see_val -= trophy_val;

		// get eval val. bit number is an index in pieces&#91;color&#93;&#91;index&#93; pointing to the
		// piece.
		trophy_val = sc == WHITE ? pieces&#91;sc&#93;&#91;so&#91;sc&#93;&#93; -> getEvalVal&#40;) &#58; pieces&#91;sc&#93;&#91;so&#91;sc&#93; - 16&#93; -> getEvalVal&#40;);

		// on to the next bit!
		so&#91;sc&#93;++;

		sc = opponentColor&#40;sc&#41;;
	&#125;

	return see_val;
&#125;