From 78359960a2989cb39d7ffa176dc78f2683acd8d2 Mon Sep 17 00:00:00 2001
From: H.G.Muller <hgm@hgm-xboard.(none)>
Date: Sat, 14 Jan 2017 12:48:19 +0100
Subject: [PATCH] Keep track of attacked squares near King

The move generator now marks all attacked squares on an auxiliary board.
At the end it counts the number of such squares next to the enemy King,
empty squares and captures separately. It also counts the number of
unattacked empty squares next to the King.
---
 dropper.c |   17 +++++++++++++++--
 1 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/dropper.c b/dropper.c
index 85c44c3..219c868 100644
--- a/dropper.c
+++ b/dropper.c
@@ -691,6 +691,7 @@ typedef struct {   // move stack sectioning
     int castlings; // end of list of board moves without castlings
     int epSqr;
     int checker;
+    int safety, hole, escape;
 } MoveStack;
 
 HashEntry *hashTable;
@@ -740,20 +741,24 @@ void
 Dump (char *s)
 {int i; printf("%s\n",s); for(i=0; i<ply; i++) printf(" {%x} %s", deprec[i], MoveToText(path[i])); PrintDBoard("board", board, "   ", 11); exit(1); }
 
+#define attacks (rawAttacks + 23)
+static int attackKey, rawAttacks[13*22];
+
 int
 MoveGen (int stm, MoveStack *m, int castle)
 {   // generate all board moves, return 1 if King capture found amongst those
-    int r, f;
+    int r, f, c = ++attackKey;
     m->firstMove = m->nonCapts =  m->late = moveSP; m->stage = 0;
     for(r=0; r<boardEnd; r+=22) for(f=0; f<nrFiles; f++) {
 	int from = r + f, piece = board[from];
 	if(piece & stm) {
 	    int step, dir = 2*firstDir[piece-WHITE]; // steps data comes in pairs
 	    while((step = steps[dir++])){ // next direction
-		int range = steps[dir++], to = from, victim, inZone = zoneTab[from];
+		int range = steps[dir++], to = from, victim, inZone = zoneTab[from], d = c - (range == 11);
 		do {
 		    int move, promote, slot;
 		    victim = board[to += step];
+		    attacks[to] = d; // keep track of attacked squares (even with own piece)
 		    if(victim & stm) break; // captures own piece
 		    if(range & 2) { // divergent move: must be FIDE Pawn
 			if(to == m->epSqr) { // reaches e.p. square: must be through diagonal move, and e.p. square is always empty
@@ -808,6 +813,14 @@ MoveGen (int stm, MoveStack *m, int castle)
 	if(board[r-1] == 0 && board[r-2] == 0 && board[r-3] == 0) f += 2, moveStack[moveSP++] = r << 8 | 8*22+21 + 22*(stm == BLACK);
     }
 
+    r = location[stm+31^COLOR]; // enemy King
+#   define HOLE(X) (attacks[X] == c)*!board[X]
+    m->hole = HOLE(r+1) + HOLE(r-1) + HOLE(r+22) + HOLE(r+21) + HOLE(r+23) + HOLE(r-21) + HOLE(r-22) + HOLE(r-23);
+#   define SAFE(X) (attacks[X] == c)*!(board[X] & stm)
+    m->safety = SAFE(r+1) + SAFE(r-1) + SAFE(r+22) + SAFE(r+21) + SAFE(r+23) + SAFE(r-21) + SAFE(r-22) + SAFE(r-23);
+#   define ESC(X) (board[X] & stm || attacks[X] == c)
+    m->escape = 8 - (ESC(r+1) + ESC(r-1) + ESC(r+22) + ESC(r+21) + ESC(r+23) + ESC(r-21) + ESC(r-22) + ESC(r-23));
+
     return 0;
 }
 
-- 
1.7.0.4