Recognize castling double-moves from engine

An engine could already send double-moves of the Alien protocol,
where the same piece moved twice, which were then glued into a single
step, with the intermediate square as trampled piece. Now when the
second leg is whith a different piece, it keeps the first leg as overall
move, and tramples the second mover. This translates castlings sent
as two-piece moves to the kludge format of trampling the own 'Rook'.

diff --git a/backend.c b/backend.c
index be8956f..43df74d 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -8667,12 +8667,13 @@ FakeBookMove: // [HGM] book: we jump here to simulate machine moves after book h
            safeStrCpy(firstLeg, machineMove, 20); // just remember it for processing when second leg arrives
            return;
        } else if(firstLeg[0]) { // there was a previous leg;
-           // only support case where same piece makes two step (and don't even test that!)
+           // only support case where same piece makes two step
            char buf[20], *p = machineMove+1, *q = buf+1, f;
            safeStrCpy(buf, machineMove, 20);
            while(isdigit(*q)) q++; // find start of to-square
            safeStrCpy(machineMove, firstLeg, 20);
-           while(isdigit(*p)) p++;
+           while(isdigit(*p)) p++; // to-square of first leg (which is now copied to machineMove)
+           if(*p == *buf)          // if first-leg to not equal to second-leg from first leg says unmodified (assume it ia King move of castling)
            safeStrCpy(p, q, 20); // glue to-square of second leg to from-square of first, to process over-all move
            sscanf(buf, "%c%d", &f, &killY); killX = f - AAA; killY -= ONE - '0'; // pass intermediate square to MakeMove in global
            firstLeg[0] = NULLCHAR;