8ab9c2511a
This area has become obscure and tricky over the course of incremental changes that did not respect the original's consistency and clarity. Now, it's not clear why we use MAX_PLY = 120, or why we use MAX_PLY+6, among other things. This patch does the following: * ID loop: depth ranges from 1 to MAX_PLY-1, and due to TT constraint (depth must fit into an int8_t), MAX_PLY should be 128. * stack[]: plies now range from 0 to MAX_PLY-1, hence stack[MAX_PLY+4], because of the extra 2+2 padding elements (for ss-2 and ss+2). Document this better, while we're at it. * Enforce 0 <= ply < MAX_PLY: - stop condition is now ss->ply >= MAX_PLY and not ss->ply > MAX_PLY. - assert(ss->ply < MAX_PLY), before using ss+1 and ss+2. - as a result, we don't need the artificial MAX_PLY+6 range. Instead we can use MAX_PLY+4 and it's clear why (for ss-2 and ss+2). * fix: extract_pv_from_tt() and insert_pv_in_tt() had no reason to use MAX_PLY_PLUS_6, because the array is indexed by plies, so the range of available plies applies (0..MAX_PLY before, and now 0..MAX_PLY-1). Tested with debug compile, using MAX_PLY=16, and running bench at depth 17, using 1 and 7 threads. No assert() fired. Feel free to submit to more severe crash-tests, if you can think of any. No functional change.
Overview
Stockfish is a free UCI chess engine derived from Glaurung 2.1. It is not a complete chess program and requires some UCI-compatible GUI (e.g. XBoard with PolyGlot, eboard, Arena, Sigma Chess, Shredder, Chess Partner or Fritz) in order to be used comfortably. Read the documentation for your GUI of choice for information about how to use Stockfish with it.
This version of Stockfish supports up to 128 cores. The engine defaults to one search thread, so it is therefore recommended to inspect the value of the Threads UCI parameter, and to make sure it equals the number of CPU cores on your computer.
Files
This distribution of Stockfish consists of the following files:
-
Readme.md, the file you are currently reading.
-
Copying.txt, a text file containing the GNU General Public License.
-
src, a subdirectory containing the full source code, including a Makefile that can be used to compile Stockfish on Unix-like systems.
Compiling it yourself
On Unix-like systems, it should be possible to compile Stockfish directly from the source code with the included Makefile.
Stockfish has support for 32 or 64-bit CPUs, the hardware POPCNT instruction, big-endian machines such as Power PC, and other platforms.
In general it is recommended to run make help to see a list of make
targets with corresponding descriptions. When not using the Makefile to
compile (for instance with Microsoft MSVC) you need to manually
set/unset some switches in the compiler command line; see file types.h
for a quick reference.
Terms of use
Stockfish is free, and distributed under the GNU General Public License (GPL). Essentially, this means that you are free to do almost exactly what you want with the program, including distributing it among your friends, making it available for download from your web site, selling it (either by itself or as part of some bigger software package), or using it as the starting point for a software project of your own.
The only real limitation is that whenever you distribute Stockfish in some way, you must always include the full source code, or a pointer to where the source code can be found. If you make any changes to the source code, these changes must also be made available under the GPL.
For full details, read the copy of the GPL found in the file named Copying.txt