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=AVX2 Attacks=
Since May 2020, CFish contains experimental [[AVX2]]/[[AVX-512]] computational [[Sliding Piece Attacks|sliding piece attack]] code by Okuhara
as memory saving alternative to [[Magic Bitboards|Magic bitboards]] <ref>[https://github.com/syzygy1/Cfish/blob/master/src/avx2-bitboard.h Cfish/avx2-bitboard.h at master · syzygy1/Cfish · GitHub]</ref>. It applies a kind of [[Classical Approach#Branchless|branchless classical approach]].
For instance, the four [[Classical Approach#Positive Rays|positive rays]] and [[Classical Approach#Negative Rays|negative rays]] of a [[Queen|queen]]
are processed as vector of 4 [[Bitboards|bitboards]] in one 256-bit ymm register each. Positive and negative rays were intersected with the vector of broadcast [[Occupancy|occupancies]],
While the positive rays were processed by [[BMI1#BLSMSK|BLSMSK]] aka <code>((x-1) ^ x)</code> to clear the ray squares above the LS1B blockers,
the negative rays use a [[Parallel Prefix Algorithms#Fill Stuff|parallel prefix fill]] with three vector right shifts and ors, to clear all ray bits below the MS1B blockers.
The eight ray attack sets were vertically and two times horizontally ored together for the final result.The conditional compiled AVX-512 version takes advantage of the [[AVX-512#VPLZCNT|_mm256_lzcnt_epi64 ]] <ref>[https://software.intel.com/sites/landingpage/IntrinsicsGuide/#text=_mm256_lzcnt_epi64&expand=5560,5471,3497 _mm256_lzcnt_epi64]</ref> and [[AVX-512#VPTERNLOG|_mm256_ternarylogic_epi64 ]] <ref>[https://software.intel.com/sites/landingpage/IntrinsicsGuide/#text=_mm256_ternarylogic_epi64&expand=5560,5471,3497,5873 _mm256_ternarylogic_epi64]</ref> intrinsics.
Rook and bishop naturally suffer from less vector utilization, and combine some other well known techniques, i.e. the bishop attack getter processes only positive rays by swapping bytes.
=See also=
* [[asmFish]]
* [[Fat Titz]]
* [[Portfish]]
* [[Rustfish]]
* [http://www.talkchess.com/forum3/viewtopic.php?f=2&t=74402 Cfish is back!] by [[Louis Zulli]], [[CCC]], July 07, 2020
: [http://www.talkchess.com/forum3/viewtopic.php?f=2&t=74402&start=10 Re: Cfish is back!] by [[Ronald de Man]], [[CCC]], July 07, 2020
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=75400 Hacking around CFish NNUE] by [[Maksim Korzh]], [[CCC]], October 15, 2020 » [[NNUE]]
=External Links=
