🚀 go-pugleaf

I found a bug in gnuchess 3.1 that is worth picking up if you want to use
it with xboard or whatever.  The bug occurs if you try to undo a move that
had resulted in a pawn promotion.  Gnuchess 3.1 checks for promotion by
tracing the path of the piece back to the start of the game to see if it
was in a pawn row (pretty interesting hack to get around the fact that
there was no promotion flag!).  There is an "order of precedence" C bug
in one of the tests that makes gnuchess demote non-pawn pieces to pawns.
Of course, xboard (or Xchess in my case) does not know that gnuchess thinks
the piece is now a pawn!  Here is the fix:

Old code (in function Undo in file nondsp.c):
      /* Check for promotion: */
      if ((row (f) == 6 && row (t) == 7) || (row (f) == 1 && row (t) == 0))
	{
	  int g, from = f;
	  for (g = GameCnt - 1; g > 0; g--)
-->	    if (GameList[g].gmove & 0xFF == from)     <--
	      from = GameList[g].gmove >> 8;
	  if (row (from) == 1 || row (from) == 6)
	    board[t] = pawn;
	}

Change the above marked line to:
	    if ((GameList[g].gmove & 0xFF) == from)

This bug exists (I think) in the other "dsp" files as well, but gnuchessr
is the one you want for xboard anyway...

					Enjoy!
					Joe Peterson
					joe@avs.com