backward pawns in Stockfish

lech · Post by **lech** » Thu Jul 22, 2010 5:51 am

[d] 8/8/1p6/pPp5/P1P5/8/8/8 w - -
Are the pawn b6, a4, c4 backward (week) or not ?
Let Stockfish say what prefers.

The first patch:

// Test for backward pawn 
      if (   &#40;passed | isolated | chain&#41; 
          || &#40;ourPawns & attack_span_mask&#40;opposite_color&#40;Us&#41;, s&#41;) 
          || &#40;pos.attacks_from<PAWN>&#40;s, Us&#41; & theirPawns&#41;) 
          backward = false; 
      else 
      &#123; 
          b = this_and_neighboring_files_bb&#40;f&#41; & rank_bb&#40;Us == WHITE ? r+1 &#58; r-1&#41;; 

         while (!&#40;b & &#40;ourPawns | theirPawns&#41;)) 
              Us == WHITE ? b <<= 8 &#58; b >>= 8; 

          if &#40;b & file_bb&#40;f&#41; & theirPawns&#41; 
             backward = false; 
         else backward = &#40;b | &#40;Us == WHITE ? b << 8 &#58; b >> 8&#41;) & theirPawns; 
        &#125;

the second patch:

Code: Select all

// Test for backward pawn 
           if (   &#40;passed | isolated | chain&#41; 
          || &#40;ourPawns & attack_span_mask&#40;opposite_color&#40;Us&#41;, s&#41;) 
          || &#40;pos.attacks_from<PAWN>&#40;s, Us&#41; & theirPawns&#41;) 
          backward = false; 
      else 
      &#123; 
           b = this_and_neighboring_files_bb&#40;f&#41; & rank_bb&#40;Us == WHITE ? r+1 &#58; r-1&#41;; 

          while (!&#40;b & &#40;ourPawns | theirPawns&#41;)) 
              Us == WHITE ? b <<= 8 &#58; b >>= 8; 

          if &#40;b & file_bb&#40;f&#41; & theirPawns&#41; 
            backward = true;
         else backward = &#40;b | &#40;Us == WHITE ? b << 8 &#58; b >> 8&#41;) & theirPawns; 
        &#125;

The short match (100 games; 1 min/game) won the second patch +39 -32 =29.
Marco was right.

It seems that the second patch should be tested against original SF, not the first.

(I tried it .....

)

bob · Post by **bob** » Thu Jul 22, 2010 7:36 am

lech wrote:[d] 8/8/1p6/pPp5/P1P5/8/8/8 w - -
Are the pawn b6, a4, c4 backward (week) or not ?
Let Stockfish say what prefers.

The first patch:

Code: Select all

// Test for backward pawn 
      if (   &#40;passed | isolated | chain&#41; 
          || &#40;ourPawns & attack_span_mask&#40;opposite_color&#40;Us&#41;, s&#41;) 
          || &#40;pos.attacks_from<PAWN>&#40;s, Us&#41; & theirPawns&#41;) 
          backward = false; 
      else 
      &#123; 
          b = this_and_neighboring_files_bb&#40;f&#41; & rank_bb&#40;Us == WHITE ? r+1 &#58; r-1&#41;; 

         while (!&#40;b & &#40;ourPawns | theirPawns&#41;)) 
              Us == WHITE ? b <<= 8 &#58; b >>= 8; 

          if &#40;b & file_bb&#40;f&#41; & theirPawns&#41; 
             backward = false; 
         else backward = &#40;b | &#40;Us == WHITE ? b << 8 &#58; b >> 8&#41;) & theirPawns; 
        &#125;

the second patch:

Code: Select all

// Test for backward pawn 
           if (   &#40;passed | isolated | chain&#41; 
          || &#40;ourPawns & attack_span_mask&#40;opposite_color&#40;Us&#41;, s&#41;) 
          || &#40;pos.attacks_from<PAWN>&#40;s, Us&#41; & theirPawns&#41;) 
          backward = false; 
      else 
      &#123; 
           b = this_and_neighboring_files_bb&#40;f&#41; & rank_bb&#40;Us == WHITE ? r+1 &#58; r-1&#41;; 

          while (!&#40;b & &#40;ourPawns | theirPawns&#41;)) 
              Us == WHITE ? b <<= 8 &#58; b >>= 8; 

          if &#40;b & file_bb&#40;f&#41; & theirPawns&#41; 
            backward = true;
         else backward = &#40;b | &#40;Us == WHITE ? b << 8 &#58; b >> 8&#41;) & theirPawns; 
        &#125;

The short match (100 games; 1 min/game) won the second patch +39 -32 =29.
Marco was right.

It seems that the second patch should be tested against original SF, not the first.

(I tried it .....

)

The major problem above is the number of games. The error bar will be larger than the difference in ratings, which makes any conclusion nothing more than a guess...

This is the perfect way to take two steps backward for every one step forward...

Justin Sherron · Post by **Justin Sherron** » Sat Jul 24, 2010 4:12 am

Hi Marek,

Have you continued to test this second patch? I've played (only) 300 90-second games, but this patch scored an impressive ~55% against my compile of the original code (55, 53.5, and 56% in 3 separate 100 game matches). Much better results than the first patch I tried

lech · Post by **lech** » Mon Jul 26, 2010 6:30 am

Justin Sherron wrote:Hi Marek,

Have you continued to test this second patch? I've played (only) 300 90-second games, but this patch scored an impressive ~55% against my compile of the original code (55, 53.5, and 56% in 3 separate 100 game matches). Much better results than the first patch I tried

Justin, I will test the second version but with one modification. I guess

it can work even better. I found two bugs in SF code. But it is another story.

mcostalba · Post by **mcostalba** » Mon Jul 26, 2010 6:41 am

lech wrote:I found two bugs in SF code. But it is another story.

Could you please report them ?

Thanks.

lech · Post by **lech** » Mon Jul 26, 2010 6:51 am

mcostalba wrote:
lech wrote:I found two bugs in SF code. But it is another story.
Could you please report them ?

Thanks.

Of course, why not ?

First:

Code: Select all

 evaluate_unstoppable_pawns
if &#40;d < 0 || pathDefended&#41;
            &#123;
                int mtg = RANK_8 - relative_rank&#40;c, s&#41;;

change:

Code: Select all

if &#40;d < 0 || pathDefended&#41;
            &#123;
                int mtg = RANK_8 - relative_rank&#40;c, s&#41; 
		- &#40;relative_rank&#40;c, s&#41; == RANK_2&#41;; // Double pawn push

 evaluate_passed_pawns
                   if (   &#40;squares_behind&#40;Us, s&#41; & pos.pieces&#40;ROOK, QUEEN, Them&#41;)
                    && &#40;squares_behind&#40;Us, s&#41; & pos.pieces&#40;ROOK, QUEEN, Them&#41; & pos.attacks_from<QUEEN>&#40;s&#41;))

change:

Code: Select all

               if (   &#40;squares_behind&#40;Us, s&#41; & pos.pieces&#40;ROOK, QUEEN, Them&#41;)
                    && &#40;squares_behind&#40;Us, s&#41; & pos.pieces&#40;ROOK, QUEEN, Them&#41; & pos.attacks_from<ROOK>&#40;s&#41;))

mcostalba · Post by **mcostalba** » Mon Jul 26, 2010 7:16 am

lech wrote: Of course, why not ?

The second is more an optimization then a fix, the first one is a real fix although for a very rare case.

Thanks Marek !

Justin Sherron · Post by **Justin Sherron** » Mon Jul 26, 2010 11:04 pm

Just a quick update - I made it to 500 games (I'll probably quit at that, since I was just doing it out of curiosity). The patch scored 50% and 54% in the 4th and 5th set of 100 games, for a cumulative score of 53.7% after 500 games. Of course, I'm a testing newbie and exceptionally non-talented with computers, which should be taken into consideration when reading my numbers

. But in any case, I hope it's helpful.

lech · Post by **lech** » Tue Jul 27, 2010 9:24 pm

Justin Sherron wrote:Just a quick update - I made it to 500 games (I'll probably quit at that, since I was just doing it out of curiosity). The patch scored 50% and 54% in the 4th and 5th set of 100 games, for a cumulative score of 53.7% after 500 games. Of course, I'm a testing newbie and exceptionally non-talented with computers, which should be taken into consideration when reading my numbers . But in any case, I hope it's helpful.

I tested the second patch:

Code: Select all

// Test for backward pawn 
           if (   &#40;passed | isolated | chain&#41; 
          || &#40;ourPawns & attack_span_mask&#40;opposite_color&#40;Us&#41;, s&#41;) 
          || &#40;pos.attacks_from<PAWN>&#40;s, Us&#41; & theirPawns&#41;) 
          backward = false; 
      else 
      &#123; 
           b = this_and_neighboring_files_bb&#40;f&#41; & rank_bb&#40;Us == WHITE ? r+1 &#58; r-1&#41;; 

          while (!&#40;b & &#40;ourPawns | theirPawns&#41;)) 
              Us == WHITE ? b <<= 8 &#58; b >>= 8; 

          if &#40;b & file_bb&#40;f&#41; & theirPawns&#41; 
            backward = true; 
         else backward = &#40;b | &#40;Us == WHITE ? b << 8 &#58; b >> 8&#41;) & theirPawns; 
        &#125;

with optimization:

Code: Select all

C++
general
debug information format - disabled
optimization
optimization - maximize speed
favor size or speed - favor fast code
code generation
basics runtime checks - default

and command line:

Code: Select all

cutechess-cli.exe -fcp name=sfx cmd=sfx.exe -scp name=sf cmd=sf.exe -both proto=uci option.Threads=2 option.Ponder=false book=book.bin bookdepth=12 option.Hash=64 tc=/0&#58;30+0 -resign 3 700 -wait 1000 -games 100 -repeat

sfx size: 469 504
sf size: 468 992
Now it seems to be ok.

After 100 games: sfx vs sf: +33 -22 =45

I will continue test tomorow.

A try to improve this patch doesn't work.

backward pawns in Stockfish

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