Optimize Magics

[mstembera]

Reduce the size of the Magics table by half on modern cpu's and lay it out to match our access pattern. Namely we typically access the magics for the same square for both bishop and rook back to back so we want those to be in the same cache line.

https://tests.stockfishchess.org/tests/view/6701c9b386d5ee47d953bcf4
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 121664 W: 31931 L: 31497 D: 58236
Ptnml(0-2): 395, 13658, 32322, 14032, 425

A similar patch minus the size reduction finished yellow
https://tests.stockfishchess.org/tests/view/6695f03f4ff211be9d4ec16c
LLR: -2.94 (-2.94,2.94) <0.00,2.00>
Total: 310688 W: 80940 L: 80746 D: 149002
Ptnml(0-2): 1119, 35032, 82846, 35230, 1117

No functional change
bench: 1511354

[github-actions]

clang-format 18 needs to be run on this PR.
If you do not have clang-format installed, the maintainer will run it when merging.
For the exact version please see https://packages.ubuntu.com/noble/clang-format-18.

(execution 11205050881 / attempt 1)

[Disservin]

a while ago @sqrmax tried doing something like this, not sure if this was ever submitted to fishtest ?
master...sqrmax:Stockfish:magics-experiment

[cj5716]

BTW - I do not think this reduces the size of the magics table at all given it just goes from 2 1D tables to 1 2D table.

as for the sqrmax test - I recall seeing it on fishtest at some point but can't confirm

[AndyGrant]

I believe this is what he is referring to when he says the tables are cut in half. Which is true. The underlying magic lookups are still the same size, however. Just this meta-wrapper per-square.

[cj5716]

I see, thanks

[mstembera]

Yes sizeof(Magic) is now 16 bytes instead of 32 bytes on machines w/ pext. Also importantly the table is now
Magics[SQUARE_NB][2]; and not just Magics[2][SQUARE_NB]; which puts corresponding bishop and rook squares next to each other in memory. I missed the patch by @sqrmax but have no problem giving him credit w/ this PR.