feat(core): add precomputed bitboard tables

Bitboards.scala

@@ -0,0 +1,131 @@
+package gambit
+
+object Bitboards:
+  inline def sq64(sq: Int): Int = Square.rankOf(sq) * 8 + Square.fileOf(sq)
+  inline def fileOf(s: Int): Int = s & 7
+  inline def rankOf(s: Int): Int = s >> 3
+  inline def bit(s: Int): Long = 1L << s
+  inline def count(bb: Long): Int = java.lang.Long.bitCount(bb)
+
+  val fileMask: Array[Long] =
+    val out = new Array[Long](8)
+    var f = 0
+    while f < 8 do
+      var r = 0
+      while r < 8 do
+        out(f) |= bit(r * 8 + f)
+        r += 1
+      f += 1
+    out
+
+  val rankMask: Array[Long] =
+    val out = new Array[Long](8)
+    var r = 0
+    while r < 8 do
+      var f = 0
+      while f < 8 do
+        out(r) |= bit(r * 8 + f)
+        f += 1
+      r += 1
+    out
+
+  val adjacentFiles: Array[Long] =
+    val out = new Array[Long](8)
+    var f = 0
+    while f < 8 do
+      if f > 0 then out(f) |= fileMask(f - 1)
+      if f < 7 then out(f) |= fileMask(f + 1)
+      f += 1
+    out
+
+  private val forwardRanksWhite: Array[Long] =
+    val out = new Array[Long](8)
+    var r = 0
+    while r < 8 do
+      var rr = r + 1
+      while rr < 8 do
+        out(r) |= rankMask(rr)
+        rr += 1
+      r += 1
+    out
+
+  private val forwardRanksBlack: Array[Long] =
+    val out = new Array[Long](8)
+    var r = 0
+    while r < 8 do
+      var rr = r - 1
+      while rr >= 0 do
+        out(r) |= rankMask(rr)
+        rr -= 1
+      r += 1
+    out
+
+  val passedWhite: Array[Long] =
+    val out = new Array[Long](64)
+    var s = 0
+    while s < 64 do
+      val f = fileOf(s)
+      val span = fileMask(f) | adjacentFiles(f)
+      out(s) = span & forwardRanksWhite(rankOf(s))
+      s += 1
+    out
+
+  val passedBlack: Array[Long] =
+    val out = new Array[Long](64)
+    var s = 0
+    while s < 64 do
+      val f = fileOf(s)
+      val span = fileMask(f) | adjacentFiles(f)
+      out(s) = span & forwardRanksBlack(rankOf(s))
+      s += 1
+    out
+
+  val frontFileWhite: Array[Long] =
+    val out = new Array[Long](64)
+    var s = 0
+    while s < 64 do
+      out(s) = fileMask(fileOf(s)) & forwardRanksWhite(rankOf(s))
+      s += 1
+    out
+
+  val frontFileBlack: Array[Long] =
+    val out = new Array[Long](64)
+    var s = 0
+    while s < 64 do
+      out(s) = fileMask(fileOf(s)) & forwardRanksBlack(rankOf(s))
+      s += 1
+    out
+
+  val kingRing: Array[Long] =
+    val out = new Array[Long](64)
+    val steps = Array((1, 0), (-1, 0), (0, 1), (0, -1), (1, 1), (1, -1), (-1, 1), (-1, -1))
+    var s = 0
+    while s < 64 do
+      val f = fileOf(s)
+      val r = rankOf(s)
+      var mask = bit(s)
+      var i = 0
+      while i < steps.length do
+        val nf = f + steps(i)._1
+        val nr = r + steps(i)._2
+        if nf >= 0 && nf < 8 && nr >= 0 && nr < 8 then mask |= bit(nr * 8 + nf)
+        i += 1
+      out(s) = mask
+      s += 1
+    out
+
+  val knightAttacks: Array[Long] =
+    val out = new Array[Long](64)
+    val steps = Array((1, 2), (2, 1), (2, -1), (1, -2), (-1, -2), (-2, -1), (-2, 1), (-1, 2))
+    var s = 0
+    while s < 64 do
+      val f = fileOf(s)
+      val r = rankOf(s)
+      var i = 0
+      while i < steps.length do
+        val nf = f + steps(i)._1
+        val nr = r + steps(i)._2
+        if nf >= 0 && nf < 8 && nr >= 0 && nr < 8 then out(s) |= bit(nr * 8 + nf)
+        i += 1
+      s += 1
+    out