Outputs ambiguous moves

[sesse]

Fathom occasionally does not disambiguate moves properly:

sesse@pannekake:~> fathom --path=/srv/syzygy '2Q5/6P1/8/8/8/1k5K/8/2Q5 w - - 1 16'
--path=/srv/syzygy 2Q5/6P1/8/8/8/1k5K/8/2Q5 w - - 1 16
[Event ""]
[Site ""]
[Date "??"]
[Round "-"]
[White "Syzygy"]
[Black "Syzygy"]
[Result "1-0"]
[FEN "2Q5/6P1/8/8/8/1k5K/8/2Q5 w - - 1 16"]
[WDL "Win"]
[DTZ "1"]
[WinningMoves "Kg2, Kh2, Kg3, Kg4, Kh4, Qa1, Qb1, Qd1, Qe1, Qf1, Qg1, Qh1, Qb2, Qcc2, Qd2, Qa3, Qcc3, Qe3, Qcc4, Qf4, Qcc5, Qg5, Qcc6, Qh6, Qcc7, Qcc2, Qcc3, Qcc4, Qg4, Qcc5, Qf5, Qa6, Qcc6, Qe6, Qb7, Qcc7, Qd7, Qa8, Qb8, Qd8, Qe8, Qf8, Qg8, Qh8, g8=Q, g8=N, g8=R, g8=B"]
[DrawingMoves ""]
[LosingMoves ""]

16. Qcc4# 1-0

The problem is that there are two white queens on the c file; one on c1 and on c8. (Granted, only one of them can checkmate, but checks and checkmates are not used for disambiguation; see the PGN standard, section 8.2.3.5. In any case, “c” is redundant.) Also note that Qcc4 is output twice in the WinningMoves list.

The correct disambiguation in this case would be Q8c4#.

[sesse]

Perhaps something like this:

diff --git a/src/apps/fathom.c b/src/apps/fathom.c
index e58406b..2e610ea 100644
--- a/src/apps/fathom.c
+++ b/src/apps/fathom.c
@@ -326,9 +326,9 @@ static void move_to_str(const struct pos *pos, unsigned move, char *str)
         *str++ = 'a' + f;
     else if (tb_pop_count(att) > 1)
     {
-        if (tb_pop_count(att & (BOARD_FILE_A >> f)) <= 1)
+        if (tb_pop_count(att & (BOARD_RANK_1 << (8 * r))) <= 1)
             *str++ = 'a' + f;
-        else if (tb_pop_count(att & (BOARD_RANK_1 >> r)) <= 1)
+        else if (tb_pop_count(att & (BOARD_FILE_A << f)) <= 1)
             *str++ = '1' + r;
         else
         {

[jdart1]

Fixed in https://github.com/jdart1/Fathom/commit/59f96c00e9762672eb36006b6aeb9b9338864ba3