https://github.com/niklasf/magics

Finding magic factors for bitboard based move generation
https://github.com/niklasf/magics

bitboard chess hashtable

Last synced: 2 months ago
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Finding magic factors for bitboard based move generation

• Host: GitHub
• URL: https://github.com/niklasf/magics
• Owner: niklasf
• License: gpl-3.0
• Created: 2018-04-08T12:49:38.000Z (over 6 years ago)
• Default Branch: master
• Last Pushed: 2022-12-09T05:21:00.000Z (about 2 years ago)
• Last Synced: 2024-05-01T18:57:56.841Z (8 months ago)
• Topics: bitboard, chess, hashtable
• Language: C
• Size: 2.02 MB
• Stars: 12
• Watchers: 4
• Forks: 2
• Open Issues: 1
• Metadata Files:
  • Readme: README.md
  • Funding: .github/FUNDING.yml
  • License: LICENSE.txt

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README

        
Finding magic factors for bitboard based move generation

========================================================

Tool to find factors for [Magic bitboards](https://www.chessprogramming.org/Magic_Bitboards).

Exhaustive search

-----------------

When looking for magic factors `m` with shift `w` it is sufficient to look

in the range `2^{64 - w - lsb(r_max)} <= m < 2^{64 - lsb(r_max)}` where

`r_max` is the maximum relevant occupancy for the square [1].

Tricks for fast testing

-----------------------

1. Avoid zero filling table (like Stockfish).

2. Dynamically reorder relevant occupancies to fail earlier on average.

![Performance comparison](/fig-benchmark-rf8.png)

*Performance based on search of improved rook magics for f8.*

Tools

-----

### `verify.py `

Verifies a magic candidate.

### `v1/magics `

Select `BISHOP` or `ROOK`, `SQUARE` and `EASY_SHIFT` in `v1/Makefile`,

`make` and run `./magics `. Tests all candidates in the specified range.

### `v2/daq`

Select `BISHOP` or `ROOK`, `SQUARE` and `SHIFT` in `v2/Makefile`,

`make` and run `./daq`. Counts all magics with the specified settings.

### `cuda/test`

Select square, piece type and shift in `generate.py`.

`make` and run `./test` to find magic factors with the specified

shift or disprove their existence. Works best for bishop squares (with small

shifts and small table sizes).

References

----------

1. [Disproving the existence of some magics](http://www.talkchess.com/forum/viewtopic.php?t=65187). 2017.

2. [No bishop magics with fixed shift 8](http://www.talkchess.com/forum/viewtopic.php?t=67051). 2018.