====== Chess - Programming - Database ======

My propriety database format to hold a record of every move.

^Field^Bits^Range^Comment^
|Move From|6|A1=0, H1=7, A8=56, H8=63|File=<file>-'A', rank=<rank>-'1'. Castle and Enpassant moves are assumed to be valid moves.|
|Move To|6|A1=0, H1=7, A8=56, H8=63|File=<file>-'A', rank=<rank>-'1'. Castle and Enpassant moves are assumed to be valid moves.|
|Promotion Type|3|000-111|000=unused, 001=Knight, 010=Bishop, 011=Rook, 100=Queen.|
|White Elo|11|0-2047|Actual elo of white – 1000.|
|Elo Diff|8|0-255|0-255=w, 256-511=b.|
|Elo Diff Neg|1|0-1|0=positive, 1=negative.|
|%WDL|9|0-511|0-99=Percentage Win, 100-199=Percentage Draw, 200-299=Percentage Loss. From White Perspective. Unused Values 300-511.|
|Count|12|0-4095|Rolling.|
|Weight|8|0-255|A measure for the likelihood of a win after that particular move has been made. 0-127=w, 128-255=b. Default is to use ELO changes to calculate this.|


<WRAP info>
**NOTE:**  A total of 64-bits.
</WRAP>


----

===== Moves =====

Moves are stored in format:

  * A1 = 0, H1 = 7, A8 = 56, H8 = 63.
  * File = <file> - 'A', row = <rank> - '1'.
  * Castle and Enpassant moves are assumed to be valid moves.

----

===== Promotion Type =====

Assumed that the associated moves are for a pawn and this promotion is valid.

----

===== White Elo =====

The average of the ELO rating for the White player - 1000.

----

===== Elo Diff & Elo Diff Neg =====

Used to calculate the ELO rating of the Black Player.

Either add, or subtract this figure from the **White Elo**.

  * If **Elo Diff Neg** is set, then subtract, otherwise add.

----

===== %WDL =====

The percentage of Wins, Draws and Losses for the White Player.

  * Obviously, the Black Player would be the opposite.

^Values^Description^
|0-99|Percent of Wins.|
|100-199|Percent of Draws.|
|200-299|Percent of Losses.|
|300-511|Unused Values.|

----

===== Count =====

The number of games having played this move.

A maximum of 4096 games is recorded.

The other fields using this figure for their calculations, such as %WDL, should be recalculated / updated even though this maximum number of 4096 is reached.

----

===== Weight =====

A measure for the likelihood of a win after that particular move has been made.  

Range is 0-255.

Default is to use ELO changes per this formula:

<code>
  white_probability = (1.0 / (1.0 + std::pow(10.0, ((rating1 - rating2) / 400.0)) ) );
  black_probability = 1 - white_probability;

  if (rating1 > rating2)
  {
    result=-black_probability/20;
  }
  else
  if (rating1 < rating2)
  {
    res=white_probability/20;
  }
</code>

<WRAP info>
**NOTE:**  A bespoke formula could be used to update this weighting.

  * Instead of using the k factor/value of 400 that the original formula uses, this is changed to be 100 + ((score difference) * 2).
  * So the max k factor would be 140 (20-0 is the biggest win, multiply by 2, add to 100).
</WRAP>


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[[Chess:Programming:Database|Database]]