No Zobrist key

[cdani]

Mersenne twister is a good generator and they had 1000 64 bits numbers on the page (I can't find now)

http://www.math.sci.hiroshima-u.ac.jp/~ ... T/emt.html

[flok]

Code: Select all

        public override int GetHashCode()
        {
            int hash = 0;
            for &#40;int i = 0; i < SIZE-1; i++)
            &#123;
                hash += &#40;int&#41;&#40;rep&#91;i&#93; % 13&#41;;
                hash = &#40;hash << 4&#41;;
               
            &#125;
            hash += &#40;int&#41;&#40;rep&#91;SIZE-1&#93; % 13&#41;;


            return hash;
        &#125;

Maybe this is better. At least I understand it. Collecting 8 times four bits because hash code must be 32 bits. Largest prime for four bits is 13.

Can you explain why this is a good hash?
Did you test how often it has collisions?

[Henk]

Code: Select all

        public override int GetHashCode()
        {
            int hash = 0;
            for &#40;int i = 0; i < SIZE-1; i++)
            &#123;
                hash += &#40;int&#41;&#40;rep&#91;i&#93; % 13&#41;;
                hash = &#40;hash << 4&#41;;
               
            &#125;
            hash += &#40;int&#41;&#40;rep&#91;SIZE-1&#93; % 13&#41;;


            return hash;
        &#125;

Maybe this is better. At least I understand it. Collecting 8 times four bits because hash code must be 32 bits. Largest prime for four bits is 13.

Can you explain why this is a good hash?
Did you test how often it has collisions?

I don't know if it is a good hash but I understand the code. Might be it is a bad hash with many collisions but I don't think it makes my engine play worse.

Best is to switch too Zobrist key but maybe that is a waste of time.

[Daniel Anulliero]

Mersenne twister is a good generator and they had 1000 64 bits numbers on the page (I can't find now)

http://www.math.sci.hiroshima-u.ac.jp/~ ... T/emt.html

Yes I know the site Daniel but it's the 1000 numbers I can't find in it

[AndrewGrant]

http://www.math.sci.hiroshima-u.ac.jp/~ ... 64.out.txt

Took me 15 seconds. Come on :)

[Daniel Anulliero]

http://www.math.sci.hiroshima-u.ac.jp/~ ... 64.out.txt

Took me 15 seconds. Come on

Cool Andrew lol
You know I am an old man now , with less vision !!

[stegemma]

Properties side to move, castling rights, ep target square are stored in

Code: Select all

rep[7] = board.Other;

If you know a much simpler and still effective formula to compute a hash key then that would be better. For I don't like mystic code. Might be I found it somewhere on internet. Can't remember.

This is my last version of my "mystic" code to generate hash, already discussed in another thread:

Code: Select all

	uint64_t _URandS(uint64_t &seed0, uint64_t &seed1)
	{
		uint64_t x = seed0;
		const uint64_t y = seed1;
		seed0 = y;
		x ^= x << 23; // a
		x ^= x >> 17; // b
		x ^= y ^ &#40;y >> 26&#41;; // c
		seed1 = x;
		return x + y;
	&#125;

	uint64_t clsBoard&#58;&#58;GetBookHash&#40;) const
	&#123;
		// NB&#58; non cambiare mai questa definizione, per non perdere i libri già compilati!!!
		#define HH&#40;a&#41; seeds&#91;0&#93; ^= &#40;a&#41;; boBookHash ^= _URandS&#40;seeds&#91;0&#93;, seeds&#91;1&#93;);
		uint64_t seeds&#91;&#93; = &#123; 0xA10E014701010401ULL, 0x02C070202CDE2ULL &#125;;
		uint64_t boBookHash = boBits&#91;boAllPieces&#93;;
		HH&#40;boBits&#91;boKings&#93;)
		HH&#40;boBits&#91;boQueens&#93;)
		HH&#40;boBits&#91;boRooks&#93;)
		HH&#40;boBits&#91;boBishops&#93;)
		HH&#40;boBits&#91;boKnights&#93;)
		HH&#40;boBits&#91;boPawns&#93;)
		HH&#40;color&#41;
		HH&#40;boBits&#91;boFriends&#93;)
		HH&#40;boBits&#91;boEnpPawn&#93; - boBits&#91;boCastlings&#93;)
		return boBookHash;
	&#125;

It is a little crazy but it works

[Henk]

I use this key for hash table.

Code: Select all

 
        public Key(IChessBoardBits board)
        {
            rep = new ulong[SIZE];
            rep[0] = board.Pawns;
            rep[1] = board.Kings;
            rep[2] = board.Knights;
            rep[3] = board.Bishops;
            rep[4] = board.Rooks;
            rep[5] = board.Queens;
            rep[6] = board.WhitePieces;
            rep[7] = board.Other;
        }

        public bool Equals(Key key)
        {
            for &#40;int i = 0; i < SIZE; i++)
            &#123;
                if &#40;rep&#91;i&#93; != key&#91;i&#93;) return false;
            &#125;
            return true;
        &#125;

        

        public override int GetHashCode&#40;)
        &#123;
            int hash, i;
            for &#40;hash = i = 0; i < SIZE; ++i&#41;
            &#123;
                for &#40;int j = 0; j < 4; j++)
                &#123;
                    hash += &#40;int&#41;&#40;rep&#91;i&#93; >> &#40;j * 8&#41;);
                    hash += &#40;hash << 10&#41;;
                    hash ^= &#40;hash >> 6&#41;;
                &#125;
            &#125;
            hash += &#40;hash << 3&#41;;
            hash ^= &#40;hash >> 11&#41;;
            hash += &#40;hash << 15&#41;;
          
          
            return hash;
         &#125;

And I wonder if it does make my engine slow and if Zobrist key would be much better. But hash table is not used in qSearch.

[Don't ask how GetHashCode works for it's abracadabra to me now]

Found it. It was copied from this site.

https://en.wikipedia.org/wiki/Jenkins_hash_function

[hgm]

If you calculate the hash for the entire board from scratch in every node it doesn't really matter much what method you use. It will always be orders of magnitude too slow.

[Henk]

Yes. Zobrist key is better but still don't know if it is worth while to change my code.

By the way I forget a % 256 when extracting a byte.

Code: Select all

 //Jenkins hash function
        public override int GetHashCode()
        {
            int hash, i;
            for &#40;hash = i = 0; i < SIZE; ++i&#41;
            &#123;
                for &#40;int j = 0; j < 4; j++)
                &#123;
                    var octet = &#40;int&#41;(&#40;rep&#91;i&#93; >> &#40;j * 8&#41;) % 256&#41;;
                    hash += octet;
                    hash += &#40;hash << 10&#41;;
                    hash ^= &#40;hash >> 6&#41;;
                &#125;
            &#125;
            hash += &#40;hash << 3&#41;;
            hash ^= &#40;hash >> 11&#41;;
            hash += &#40;hash << 15&#41;;


            return hash;
        &#125;

Might be this is faster:
http://www.isthe.com/chongo/tech/comp/f ... #FNV-param

Code: Select all

  // FNV hash function
        public override int GetHashCode()
        {
            unchecked
            {
                int hash = (int)2166136261;

                for &#40;int i = 0; i < SIZE; ++i&#41;
                &#123;
                    for &#40;int j = 0; j < 4; j++)
                    &#123;
                        hash *= 16777619;
                        var octet = &#40;int&#41;(&#40;rep&#91;i&#93; >> &#40;j * 8&#41;) % 256&#41;;
                        hash ^= octet;

                    &#125;
                &#125;
                return hash;
            &#125;
        &#125;