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[board] Add some notes about board geometry

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Eryn Wells 2024-01-06 17:02:07 -08:00
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commit 35756e28cf
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Notes.md
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@ -4,6 +4,38 @@ Notes on Building Chess Engines
BitBoards
---------
### Mapping
Little-Endian Rank-File (LERF) Mapping maps squares to bit offsets (or indexes) from a1 to h8.
```
+-----------------+
8| 0 0 0 0 0 0 0 0 |
7| 0 0 0 0 0 0 0 0 |
6| 0 0 0 0 0 0 0 0 |
5| 0 0 0 0 0 0 0 0 |
4| 0 0 0 0 0 0 0 0 |
3| 0 0 0 0 0 0 0 0 |
2| 0 0 0 0 0 0 0 0 |
1| 0 0 0 0 0 0 0 0 |
+-----------------+
A B C D E F G H
```
```
+-----------------+
8| 1 0 0 0 0 0 0 0 |
7| 1 0 0 0 0 0 0 0 |
6| 1 0 0 0 0 0 0 0 |
5| 1 0 0 0 0 0 0 0 |
4| 1 0 0 0 0 0 0 0 |
3| 1 0 0 0 0 0 0 0 |
2| 1 0 0 0 0 0 0 0 |
1| 1 0 0 0 0 0 0 0 |
+-----------------+
A B C D E F G H
```
### Counting Bit Sets
https://graphics.stanford.edu/%7Eseander/bithacks.html#CountBitsSetParallel