Stormphranj

a work-in-progress UCI shatranj engine based on Stormphrax, with NNUE evaluation trained from zero knowledge starting with random weights

Strength

??

Features

• standard PVS with quiescence search and iterative deepening
  • aspiration windows
  • check extensions
  • countermoves
  • futility pruning
  • history
    • capture history
    • 1-ply continuation history (countermove history)
    • 2-ply continuation history (follow-up history)
    • 4-ply continuation history
  • internal iterative reduction
  • killers (1 per ply)
  • late move reductions
  • late move pruning
  • mate distance pruning
  • multicut
  • nullmove pruning
  • reverse futility pruning
  • SEE move ordering and pruning
  • singular extensions
    • double extensions
    • triple extensions
    • various negative extensions
  • Syzygy tablebase support
• NNUE
  • _
• BMI2 attacks in the bmi2 build, otherwise fancy black magic
  • pext/pdep for rooks
• lazy SMP
• static contempt

To-do

• make it stronger uwu

UCI options

Name	Type	Default value	Valid values	Description
Hash	integer	64	[1, 131072]	Memory allocated to the transposition table (in MB).
Clear Hash	button	N/A	N/A	Clears the transposition table.
Threads	integer	1	[1, 2048]	Number of threads used to search.
UCI_ShowWDL	check	true	false, true	Whether Stormphranj displays predicted win/draw/loss probabilities in UCI output.
Move Overhead	integer	10	[0, 50000]	Amount of time Stormphranj assumes to be lost to overhead when making a move (in ms).
EvalFile	string	<internal>	any path, or <internal>	NNUE file to use for evaluation.

Builds

avx512: requires AVX-512 (Zen 4, Skylake-X)
avx2-bmi2: requires BMI2 and AVX2 and assumes fast pext and pdep (i.e. no Bulldozer, Piledriver, Steamroller, Excavator, Zen 1, Zen+ or Zen 2)
avx2: requires BMI and AVX2 - primarily useful for pre-Zen 3 AMD CPUs back to Excavator
sse41-popcnt: needs SSE 4.1 and popcnt - for older x64 CPUs

Alternatively, build the makefile target native for a binary tuned for your specific CPU (see below)

Note:

• If you have an AMD Zen 1 (Ryzen x 1xxx), Zen+ (Ryzen x 2xxx) or Zen 2 (Ryzen x 3xxx) CPU, use the avx2 build even though your CPU supports BMI2. These CPUs implement the BMI2 instructions pext and pdep in microcode, which makes them unusably slow for Stormphranj's purposes.

Building

Requires Make and a competent C++20 compiler that optionally supports LTO. GCC is not currently supported, so the usual compiler is Clang.

> make <BUILD> CXX=<COMPILER>

• replace <COMPILER> with your preferred compiler - for example, clang++ or icpx
  • if not specified, the compiler defaults to clang++
• replace <BUILD> with the binary you wish to build - native/avx512/avx2-bmi2/avx2/sse41-popcnt
  • if not specified, the default build is native
• if you wish, you can have Stormphranj include the current git commit hash in its UCI version string - pass COMMIT_HASH=on

By default, the makefile builds binaries with profile-guided optimisation (PGO). To disable this, pass PGO=off. When using Clang with PGO enabled, llvm-profdata must be in your PATH.