This is a follow-up question to Is Houdini 6 a Stockfish clone?

Houdini 6.03 included a bugfix: "Correction for incorrect detection of stalemate in positions with white pawn capture moves."

If Houdini is a Stockfish clone, then this bug should also have been in Stockfish. Was it?

1 Answer 1


Reviewing the Stockfish Issues/Bugs and commits & Releases on GitHub

would indicate that this has not been logged as an issue or a bug. In addition I am unable to locate any instances of users reporting the same faults that Houdini had with Stockfish.

In addition if you review the commit difference between version 8 and 9 it is also not addressed in that release (or any other future releases to my knowledge)

Potential Resons why the bug exists in Houdini and not Stockfish

The question implies that there are no code changes between Stockfish and Houdini.

This is largely the case. The code more or less went through a google translate function. The algorithms with how it calculates the strength of positions and moves remains entirely unchanged. They added a expletitive multiplier on the output for the calculations / second which buffed the number by 8% or something crazy. Whole bunch of dodgy stuff. The program was basically identical but Dutch.

One thing I did notice that was different when all this came out and the source code was flying around; Was the weighting of pieces in stages of the game. I am not going to go through it programmatically (partially because I can't seem to find the code anymore) but a simplification on what is occurring is the following;

StockFish gives pieces a value based of a theoretical weighting depending on the position of the game (or more specifically how it interprets the stage of the game);

Lets say hypothetically stockfish evaluates it as;

  • MidGame Pawn = 150
  • EndGame Pawn = 250
  • Midgame Bishop = 500
  • EndGame Bishop = 600

Houdini does the exact same thing, but someone didn't agree with the overall evaluation that the folks behind stockfish thinks, they do it hypothetically like the following.

  • Midgame Pawn = 100
  • Endgame Pawn = 300
  • Midgame Bishop = 500
  • Endgame Bishop = 750

Say on the board White has 1 Bishop 2 Pawns , Black has 5 Pawns. Effectively the difference is;

  • Stockfish : White, 1100 Black, 1250 (+/-12% Eval difference)
  • Houdini : White, 1350 Black, 1500 (+/-10% Eval difference)

Now fundamentally the code is identical but slight variable changes can have an impact on the output. Now this is the next thing; who's weighting is correct? Considering Stockfish (to my knowledge happy to be proven wrong) have not released a version update indicating a "fix" for this issue that Houdini had, I would say ... Stockfish probably evaluated it right.

To summarise it would appear , that Houdini is largely a dutch translation of source code of stockfish. It would make sense that Stockfish would be bound by similar issues ...however the Houdini team also did change some minor things that does affect the position evaluation.

  • I upvoted, but I think the answer is better-suited to the linked question than this one, since it doesn't address the question in the OP.
    – Allure
    Aug 27, 2021 at 2:12
  • @Allure the question is answered, but also includes the the reason WHY the bug exists, and why stockfish hasn't released any updates addressing such "bug" as it isn't present in their code.
    – Dheebs
    Aug 27, 2021 at 6:38
  • Are you sure the bug isn't present in Stockfish's code? If so, that would be the answer to this question and I would suggest making it more prominent.
    – Allure
    Aug 27, 2021 at 6:45
  • I'll add an edit to the top; linking to the bugs and issues for stockfish demonstrating that it isn't addressed as a bug or an issue. In addition i'll try and track down a test position and show the Houdini and Stockfish eval which would sho the Houdini bug. My logic on answering questions isn't limited to a yes , no, maybe, there should always be an accompanying explanation as to why, which is the bulk of the post.
    – Dheebs
    Aug 27, 2021 at 6:47

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