2 files changed, 102 insertions(+), 15 deletions(-)

M src/attack.zig
M test/attack.zig

@@ 103,38 103,65 @@ pub fn maskBishopOccupancy(bishop: Square) u64 {
     const rank = sq / 8;
     const file = sq % 8;
     var bitboard: u64 = 0;
-    var r: u6 = rank + 1;
-    var f: u6 = file + 1;
-    while (r >= 1 and r <= 6 and f >= 1 and f <= 6) : ({
+    var r: u6 = rank;
+    var f: u6 = file;
+    while (r <= 6 and f <= 6) : ({
         r += 1;
         f += 1;
     }) {
         bitboard |= @as(u64, 1) << (8 * r + f);
     }
-    r = rank - 1;
-    f = file + 1;
-    while (r >= 1 and r <= 6 and f >= 1 and f <= 6) : ({
+    r = rank;
+    f = file;
+    while (r >= 1 and f <= 6) : ({
         r -= 1;
         f += 1;
     }) {
         bitboard |= @as(u64, 1) << (8 * r + f);
     }
-    r = rank + 1;
-    f = file - 1;
-    while (r >= 1 and r <= 6 and f >= 1 and f <= 6) : ({
+    r = rank;
+    f = file;
+    while (r <= 6 and f >= 1) : ({
         r += 1;
         f -= 1;
     }) {
         bitboard |= @as(u64, 1) << (8 * r + f);
     }
-    r = rank - 1;
-    f = file - 1;
-    while (r >= 1 and r <= 6 and f >= 1 and f <= 6) : ({
+    r = rank;
+    f = file;
+    while (r >= 1 and f >= 1) : ({
         r -= 1;
         f -= 1;
     }) {
         bitboard |= @as(u64, 1) << (8 * r + f);
     }
+    return resetBit(bitboard, bishop);
+}
 
-    return bitboard;
+/// Given a square occupied by a rook, return a bitboard of relevant occupancy
+/// bits.  i.e. squares on which, if other pieces are placed, the line of
+/// attack is blocked and the attack bitboard is altered.
+pub fn maskRookOccupancy(rook: Square) u64 {
+    const sq = @enumToInt(rook);
+    const rank = sq / 8;
+    const file = sq % 8;
+    var bitboard: u64 = 0;
+    var f = file;
+    var r = rank;
+    while (r <= 6) : (r += 1) {
+        bitboard |= @as(u64, 1) << (8 * r + f);
+    }
+    r = rank;
+    while (r >= 1) : (r -= 1) {
+        bitboard |= @as(u64, 1) << (8 * r + f);
+    }
+    r = rank;
+    while (f >= 1) : (f -= 1) {
+        bitboard |= @as(u64, 1) << (8 * r + f);
+    }
+    f = file;
+    while (f <= 6) : (f += 1) {
+        bitboard |= @as(u64, 1) << (8 * r + f);
+    }
+    return resetBit(bitboard, rook);
 }

@@ 129,7 129,7 @@ test "kings in corners attack only 3 squares" {
     expectEqual(bitboardFromSquares(expected_a1[0..]), kingAttacks(king_a1));
 }
 
-test "bishop in centre occupancy bits" {
+test "bishop in centre relevant occupancy bits" {
     const bishop = Square.e4;
 
     const expected_squares = [_]Square{


@@ 147,7 147,7 @@ test "bishop in centre occupancy bits" {
     expectEqual(bitboardFromSquares(expected_squares[0..]), maskBishopOccupancy(bishop));
 }
 
-test "bishop at side occupancy bits" {
+test "bishop at side relevant occupancy bits" {
     const bishop = Square.h6;
 
     const expected_squares = [_]Square{


@@ 160,3 160,63 @@ test "bishop at side occupancy bits" {
 
     expectEqual(bitboardFromSquares(expected_squares[0..]), maskBishopOccupancy(bishop));
 }
+
+test "rook in centre relevant occupancy bits" {
+    const rook = Square.d5;
+
+    const expected_squares = [_]Square{
+        Square.d6,
+        Square.d7,
+        Square.e5,
+        Square.f5,
+        Square.g5,
+        Square.d4,
+        Square.d3,
+        Square.d2,
+        Square.c5,
+        Square.b5,
+    };
+
+    expectEqual(bitboardFromSquares(expected_squares[0..]), maskRookOccupancy(rook));
+}
+
+test "rook at side relevant occupancy bits" {
+    const rook = Square.h3;
+
+    const expected_squares = [_]Square{
+        Square.h4,
+        Square.h5,
+        Square.h6,
+        Square.h7,
+        Square.h2,
+        Square.g3,
+        Square.f3,
+        Square.e3,
+        Square.d3,
+        Square.c3,
+        Square.b3,
+    };
+
+    expectEqual(bitboardFromSquares(expected_squares[0..]), maskRookOccupancy(rook));
+}
+
+test "rook in corner relevant occupancy bits" {
+    const rook = Square.a1;
+
+    const expected_squares = [_]Square{
+        Square.a2,
+        Square.a3,
+        Square.a4,
+        Square.a5,
+        Square.a6,
+        Square.a7,
+        Square.b1,
+        Square.c1,
+        Square.d1,
+        Square.e1,
+        Square.f1,
+        Square.g1,
+    };
+
+    expectEqual(bitboardFromSquares(expected_squares[0..]), maskRookOccupancy(rook));
+}