Test Legality of Shogi promotions

The old code would allow any drop, except Pawns on first and last rank,
which is actually too restrictive for Shogi (which does allow back-rank
Pawn drops). Only thing still missing is Pawn drop with mate.

diff --git a/lasker-2.2.3/src/movecheck.c b/lasker-2.2.3/src/movecheck.c
index c0dd853..1f6d69b 100644 (file)
--- a/lasker-2.2.3/src/movecheck.c
+++ b/lasker-2.2.3/src/movecheck.c
@@ -1303,6 +1303,21 @@ int legal_move(struct game_state_t * gs,
       return 0;
     if (gs->board[tFile][tRank] != NOPIECE)
       return 0;
+    if (gs->promoType == 3) { // Shogi
+      int r;
+      switch(move_piece) {
+       case PAWN:  // check for own Pawn in same file
+         for(r=0; r<gs->ranks; r++) if(gs->board[tFile][r] == (gs->onMove|PAWN)) return 0;
+       case LANCE: // Pawns and Lances not on last rank
+         if(gs->onMove == WHITE && tRank >= gs->ranks-1) return 0;
+         if(gs->onMove == BLACK && tRank < 1) return 0;
+         break;
+       case HONORABLEHORSE: // Knights at least two ranks from edge
+         if(gs->onMove == WHITE && tRank >= gs->ranks-2) return 0;
+         if(gs->onMove == BLACK && tRank < 2) return 0;
+       default: ;
+      }
+    } else
     if (move_piece == PAWN && (tRank == 0 || tRank == gs->ranks-1))
       return 0;
     return 1;