1. Introduction
---------------

Stockfish is a free UCI chess engine derived from Glaurung 2.1. It is
not a complete chess program, but requires some UCI compatible GUI
(like XBoard with PolyGlot, eboard, Josè, 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 your GUI.

This version of Stockfish supports up to 32 CPUs, but has not been
tested thoroughly with more than 4.  The program tries to detect the
number of CPUs on your computer and set the number of search threads
accordingly, but please be aware that the detection is not always
correct.  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. If you are using more than four threads, it
is recommended to raise the value of "Minimum Split Depth" UCI parameter
to 6.


2. Files
--------

This distribution of Stockfish consists of the following files:

  * Readme.txt, 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.  For further information about how to compile Stockfish
    yourself, read section 4 below.

  * polyglot.ini, for using Stockfish with Fabien Letouzey's PolyGlot
    adapter.


3. Opening books
----------------

This version of Stockfish has support for PolyGlot opening books.
For information about how to create such books, consult the PolyGlot
documentation.  The book file can be selected by setting the UCI
parameter "Book File".


4. Compiling it yourself
------------------------

On Unix-like systems, it should usually be possible to compile
Stockfish directly from the source code with the included Makefile.

For big-endian machines like Power PC you need to enable the proper
flag changing from -DNBIGENDIAN to -DBIGENDIAN in the Makefile.

Stockfish has POPCNT instruction runtime detection and support. This can
give an extra speed on Core i7 or similar systems. To enable this feature
compile with 'make icc-profile-popcnt'

On 64 bit systems the 'bsfq' assembly instruction will be used for bit
counting. Detection is automatic at compile time, but in case you experience
compile problems you can comment out #define USE_BSFQ line in types.h

In general is recommended to run 'make help' to see a list of make targets
with corresponding descriptions.


5. 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.