Introduction

Welcome to the project of translating Stockfish into assembly language. This project now uses the new assembler engine fasmg from Tomasz Grysztar. The includes in arm/includes/ or x86/include/ contain instruction and formatting macros for the four popular targets in the Building section. The hello world examples in these directories should provide enough to grasp the syntax.

Building

All versions of the executables may be built using the fasmg executable. However, fasmg is currently only available as an x86 executable. fasmg is a generic assembler which relies on the particual flavor of the assembly language to be supplied by macros. This slows down the processing of the source by a few orders of magnitute. The location of these macros (relative to the current source) is harded coded into the fish source in the variable FASMG_INC. The -e 100 switch tells fasmg to display the last 100 errors when processing the source. The -i switch inserts lines at the beginning at the source. The fish source expect that VERSION_OS is defined this way. This allows multiple versions to be assembled from the same source. Your working directory should be the root directory of this repository (the one that contains the fasmg executables)

x86-64 Linux

The x86-64 linux version links against nothing and should work with any 64 bit x86 linux kernel.

    ~/asm$ ./fasmg "x86/fish.asm" "asmfish" -e 100 -i "VERSION_OS='L'" -i "VERSION_POST = 'popcnt'"
        flat assembler  version g.hwx32
        4 passes, 18.5 seconds, 112326 bytes.
    ~/asm$ chmod 755 ./asmfish
    ~/asm$ ./asmfish bench

x86-64 Windows

The x86-64 windows version links against only kernel32.dll and should work even on XP.

    C:\asm>fasmg.exe "x86\fish.asm" "asmfish.exe" -e 100 -i "VERSION_OS='W'" -i "VERSION_POST = 'popcnt'"
        flat assembler  version g.hwx32
        5 passes, 23.2 seconds, 115200 bytes.
    C:\asm>asmfish.exe bench

x86-64 Mac

The x86-64 macOS version links against /usr/lib/libSystem.B.dylib and works on version 10.12.16.

    ~/asm$ ./fasmg "x86/fish.asm" "asmfish" -e 100 -i "VERSION_OS='X'" -i "VERSION_POST = 'popcnt'"
        flat assembler  version g.hwx32
        4 passes, 17.7 seconds, 119495 bytes.
    ~/asm$ chmod 755 ./asmfish
    ~/asm$ ./asmfish bench

aarch64 Linux

The aarch64 linux version links against nothing should work with any 64 bit arm linux kernel. Of course it can currently only be built on x86 machines.

    ~/asm$ ./fasmg "arm/fish.arm" "armfish" -e 100 -i "VERSION_OS='L'" -i "VERSION_POST = 'v8'"
        flat assembler  version g.hwx32
        3 passes, 8.1 seconds, 128018 bytes.
    ~/asm$ chmod 755 ./armfish
    ~/asm$ qemu-aarch64 ./armfish bench

Using the engine from the command line

You can feed in commands to the engine as (":" -> ";" on windows):

    ./asmfish setoption name hash value 256: go depth 5: wait

The engine quits after this if assemble flag USE_CMDLINEQUIT=1 is set. Besides the usual uci commands there are the following:

Engine options

all       pin threads to all nodes your machine in a uniform way
none      disable pinning threads to nodes
0 1 2 3   only use nodes 0, 1, 2 and 3
2         only use node 2
0.1 2.3   use nodes 0, 1, 2 and 3
            but node 1 shares per-node memory with node 0
            node 3 shares per-node memory with node 2
0.1.2.3   use nodes 0, 1, 2 and 3
            but nodes 1, 2 and 3 share per-node memory with node 0

BookDepth <= 0:
suppose the lines the book from the current position are
T0:     h2h3(30) c5d4(10) e3d4(14) g4h5(10) g2g4(11) 
        h2h3(30) g4h5(5) 
        d4c5(17) d6c5(17) b1c3(7) 
the moves g2g4(11), g4h5(5) and b1c3(7) are leaves and don't lead
to a position in the book. Triming off these leaves three times,
T1:     h2h3(30) c5d4(10) e3d4(14) g4h5(10)
        d4c5(17) d6c5(17)
T2:     h2h3(30) c5d4(10) e3d4(14)
        d4c5(17)
T3:     h2h3(30) c5d4(10)
If BookDepth = 0, probe as if it were in T0 (unchanged)
If BookDepth =-1, probe as if it were in T1 (leaves off)
If BookDepth =-2, probe as if it were in T2 (trim twice)
If BookDepth =-3, probe as if it were in T3 (trim trice)
So with BookDepth <= -3, the move d4c5 is not considered.
With BookDepth <= -5, the move h2h3 is also not considered.

BookDepth >= 1:
Book is not probed if gameply >= BookDepth

The option BestBookMove is also slightly complicated for compatibility with the cerebellum book in polyglot format. In the following pseudocode, movelist is the list of legal book moves after processing the BookDepth option. After this pseudocode if movelist is non-empty, then a random move is chosen from movelist according to the weights of these moves.

if BestBookMove = true
   if length(movelist) > 1
       filter out moves from movelist that lead to repetitions
       filter out moves from movelist without highest weight
   end if
else
   filter out moves from movelist that lead to repetitions
end if

This means that if BestBookMove=true and the first move is encoded with a higher weight than the second move (both having non-zero weight in the book), then the behaviour should match that of brainfish. If BestBookMove=false, then the only differences are

• if the first move leads to repetition and there is no second move, then the engine starts calculating
• if there are two moves, neither of which lead to a repition, then both of these moves will be considered.

               X
             X X X
           X X X X X
         X X X X X X X
         X X X X X X X
       X X X X X X X X X
     X X X X X X X X X X X
   X X X X X X X X X X X X X
-4v            0            +4v

Misbehaviour

If you observe a crash/misbehaviour in asmfish, please raise an issue here and give the following information:

• name of the executable that crashed/misbehaved
• exception code and exception offset in the case of a crash
• a log of the commands that were sent to asmFish by your gui before the crash Simply stating that asmFish crashed in your gui is useless information by itself.

asmfish is known to have problems in the fritz15 gui, while it plays much better in the fritz11 gui.

Windows might throw a "The system cannot execute the specified program." or "Insufficient system resources exist to complete the requested service.". The likely source of this problem is your virus software. Rest assured that the sources here do not produce any behaviour that is even remotely virus-like (unless you run analysis for a long time with syzygy6 installed).

FAQ

Q: Why not just start with the compiler output and speed up the critical functions? or write critical functions in asm and include them in cpp code?

A: With this approach the critical functions would still need to conform to the standards set in place by the ABI. All of the critical functions in asmFish do not conform to these standards. Plus, asmFish would be dependent on a compiler in this case, which introduces many unnecessary compilcations. Both asmFish and its assembler are around 100KB; lets keep it simple. Note that compiler output was used in the case of Ronald de Man's syzygy probing code, as this is not speed critical but cumbersome to write by hand.

Q: Is asmFish search the same as official stockfish?

A: It does now that PEDANTIC = 1 is the default! The changes previously thought to be inconsequential lose about 2 Elo in a head-to-head matchup. The functionality when using syzygy is not 100% identical because asmFish uses Ronald's original alpha-beta search while official stockfish does not. This causes minor inconsequential differences due to the piece lists.

Q: Where can I find the executable files of the old versions?

A: All older versions of asmFish/pedantFish are in the branch https://github.com/lantonov/asmFish/tree/executables

updates

For a change log, see the Wiki https://github.com/lantonov/asmFish/wiki/Change-log