射线攻击比特板

Question

我试图计算给定64位长比特板表示的索引的射线攻击：

(defn se [board index]
  "Produces a ray attack from the indexed bit in the south-east direction"
  (reduce bit-or
    (for [bit (rest (range index 0 -7))]
      (bit-flip board bit))))

rook攻击（直接沿着一个文件或等级）非常简单。然而，上述代码的问题是，我最终得到了以下对角线Bishop攻击的可能性：

00000000
00100000
01000000
10000001
00000010
00000100
00001000
00010000

我该如何解释这块木板边缘脱落的情况？我使用的是大端映射（A8=0，H1=63）。

Answer 1

我可能会使用电路板上的x，y坐标来做这件事：这使得在电路板边缘进行边界条件检查变得更容易，比如

(defn se [x y]
  "Produces a ray attack from the indexed bit in the south-east direction"
  (let [initial (bit-shift-left (bit-shift-left (long 1) x) (* y 8))
        dx 1 ;; x direction
        dy 1 ;; y direction
        distance (min 
                   (- 7 x) 
                   (- 7 y))
        shift (+ dx (* 8 dy))]
    (loop [value 0
           distance distance]
      (if (<= distance 0)
        value
        (recur (bit-or value (bit-shift-left initial (* distance shift))) (dec distance))))))

(defn bits [^long bitboard]
  (map 
    #(if (> (bit-and 1 (bit-shift-right bitboard %)) 0) 1 0)
    (range 64)))

(defn display [bitboard]
  (let [bits (partition 8 (bits bitboard))]
    (doseq [ss bits]
      (println (apply str ss)))))

(display (se 1 3))

00000000
00000000
00000000
00000000
00100000
00010000
00001000
00000100

通过一些额外的工作，您可以将其推广为向任何（dx，dy）方向投射射线，例如（1,0）对于向东移动的车。如果您设置距离限制，您甚至可以将（2,1）用于骑士......

我认为这将比为每个方向定义单独的功能更实用。

Answer 2

(defn se [board index]
  "Produces a ray attack from the indexed bit in the south-east direction"
  (reduce bit-or 0
    (for [bit (take (- 7 (rem index 8)) (rest (range index 0 -7)))]
      (bit-flip board bit))))