2 files changed, 140 insertions(+), 0 deletions(-)

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

@@ 165,3 165,92 @@ pub fn maskRookOccupancy(rook: Square) u64 {
     }
     return resetBit(bitboard, rook);
 }
+
+// Given a square occupied by a bishop and a bitboard of potentially blocking
+// pieces, return a bitboard of attack rays from the bishop which terminate if
+// the ray hits a block. The attack ray includes the blocking square.
+pub fn bishopAttackRays(bishop: Square, block: u64) u64 {
+    const sq = @enumToInt(bishop);
+    const block_minus_sq = resetBit(block, bishop);
+    const rank = @intCast(i8, sq / 8);
+    const file = @intCast(i8, sq % 8);
+    var bitboard: u64 = 0;
+    var r = rank;
+    var f = file;
+    while (r <= 7 and f <= 7) : ({
+        r += 1;
+        f += 1;
+    }) {
+        const bit = @as(u64, 1) << @intCast(u6, 8 * r + f);
+        bitboard |= bit;
+        if (bit & block_minus_sq != 0) break;
+    }
+    r = rank;
+    f = file;
+    while (r >= 0 and f <= 7) : ({
+        r -= 1;
+        f += 1;
+    }) {
+        const bit = @as(u64, 1) << @intCast(u6, 8 * r + f);
+        bitboard |= bit;
+        if (bit & block_minus_sq != 0) break;
+    }
+    r = rank;
+    f = file;
+    while (r <= 7 and f >= 0) : ({
+        r += 1;
+        f -= 1;
+    }) {
+        const bit = @as(u64, 1) << @intCast(u6, 8 * r + f);
+        bitboard |= bit;
+        if (bit & block_minus_sq != 0) break;
+    }
+    r = rank;
+    f = file;
+    while (r >= 0 and f >= 0) : ({
+        r -= 1;
+        f -= 1;
+    }) {
+        const bit = @as(u64, 1) << @intCast(u6, 8 * r + f);
+        bitboard |= bit;
+        if (bit & block_minus_sq != 0) break;
+    }
+    return resetBit(bitboard, bishop);
+}
+
+// Given a square occupied by a rook and a bitboard of potentially blocking
+// pieces, return a bitboard of attack rays from the rook which terminate if
+// the ray hits a block. The attack ray includes the blocking square.
+pub fn rookAttackRays(rook: Square, block: u64) u64 {
+    const sq = @enumToInt(rook);
+    const block_minus_sq = resetBit(block, rook);
+    const rank = @intCast(i8, sq / 8);
+    const file = @intCast(i8, sq % 8);
+    var bitboard: u64 = 0;
+    var f = file;
+    var r = rank;
+    while (r <= 7) : (r += 1) {
+        const bit = @as(u64, 1) << @intCast(u6, 8 * r + f);
+        bitboard |= bit;
+        if (bit & block_minus_sq != 0) break;
+    }
+    r = rank;
+    while (r >= 0) : (r -= 1) {
+        const bit = @as(u64, 1) << @intCast(u6, 8 * r + f);
+        bitboard |= bit;
+        if (bit & block_minus_sq != 0) break;
+    }
+    r = rank;
+    while (f >= 0) : (f -= 1) {
+        const bit = @as(u64, 1) << @intCast(u6, 8 * r + f);
+        bitboard |= bit;
+        if (bit & block_minus_sq != 0) break;
+    }
+    f = file;
+    while (f <= 7) : (f += 1) {
+        const bit = @as(u64, 1) << @intCast(u6, 8 * r + f);
+        bitboard |= bit;
+        if (bit & block_minus_sq != 0) break;
+    }
+    return resetBit(bitboard, rook);
+}

@@ 220,3 220,54 @@ test "rook in corner relevant occupancy bits" {
 
     expectEqual(bitboardFromSquares(expected_squares[0..]), maskRookOccupancy(rook));
 }
+
+test "bishop attack rays with blockers" {
+    const bishop = Square.e5;
+    const block_squares = [_]Square{
+        Square.g3,
+        Square.a1,
+        Square.d6,
+    };
+    const block = bitboardFromSquares(block_squares[0..]);
+
+    const expected_squares = [_]Square{
+        Square.f6,
+        Square.g7,
+        Square.h8,
+        Square.f4,
+        Square.g3,
+        Square.d4,
+        Square.c3,
+        Square.b2,
+        Square.a1,
+        Square.d6,
+    };
+
+    expectEqual(bitboardFromSquares(expected_squares[0..]), bishopAttackRays(bishop, block));
+}
+
+test "rook attack rays with blockers" {
+    const rook = Square.d5;
+    const block_squares = [_]Square{
+        Square.d8,
+        Square.g5,
+        Square.c5,
+    };
+    const block = bitboardFromSquares(block_squares[0..]);
+
+    const expected_squares = [_]Square{
+        Square.d6,
+        Square.d7,
+        Square.d8,
+        Square.e5,
+        Square.f5,
+        Square.g5,
+        Square.d4,
+        Square.d3,
+        Square.d2,
+        Square.d1,
+        Square.c5,
+    };
+
+    expectEqual(bitboardFromSquares(expected_squares[0..]), rookAttackRays(rook, block));
+}