From: H.G.Muller <hgm@hgm-xboard.(none)>
Date: Wed, 11 Apr 2018 07:25:00 +0000 (+0200)
Subject: Simplify CheckDrops()
X-Git-Url: http://winboard.nl/cgi-bin?a=commitdiff_plain;h=fda407162ca13f9e702aaca8a89e82738a4acc3c;p=crazywa.git

Simplify CheckDrops()

CheckDrops() tested half-way the iteration whether it should also try
dropping the unpromoted piece, based on the assumption that we must do
the Pawn iteration for dropping +P, even if dropping P is forbidden.
But in games where +P can be dropped, dropping P (in a place where it
checks) can never be forbidden!
---

diff --git a/dropper.c b/dropper.c
index 6a4ad7e..b4d10fa 100644
--- a/dropper.c
+++ b/dropper.c
@@ -946,8 +946,8 @@ CheckDrops (int stm, int king)
 {
     int i, lowest = 0;
     if(perpLoses) lowest = !!(pawnCount[sqr2file[king]] & maxBulk[stm]); // in Shogi no Pawn if file already crowded with those
-    else lowest = (stm == WHITE ? king < 2*22 : king >= 6*22);           // in zh no Pawn from back rank
-    for(i=maxDrop; i>=0; i--) {
+    else lowest = (stm == WHITE ? king < 2*22 : king >= 6*22); // in zh no Pawn from back rank
+    for(i=maxDrop; i>=lowest; i--) { // note: in games with promoDrops lowest=0 as Pawns have no bulk there
 	int piece = stm + i, from = handSlot[piece^COLOR];
 	if((signed char)board[from] < -1) { // piece type is in hand
 	    int step, dir;
@@ -961,7 +961,6 @@ CheckDrops (int stm, int king)
 		    }
 		}
 	    }
-	    if(i < lowest) break; // suppresses back-rank Pawn drops in zh
 	    dir = 2*firstDir[piece-WHITE];
 	    while((step = steps[dir++])) {
 		int to = king, range = steps[dir++];