Movegen speedup via magic bitboards (#640)

* Movegen speedup via magic bitboards

* build system support for PEXT instruction

* Removed dependency from legacy rook/bishop attack tables in initialization code

* Optimization: use pointer to square attacks table instead of offset to save some instructions

* Consistently use term 'attack line' everywhere

* Add PEXT support path

* Comment improvement

* More comment improvements

* Revert accidental board_test changes

This reverts commit 7f1374d.

* More comment improvements

* Address review comments

* Initialize magic bitboards in board_test

* Cleanup of unused code

* Initialize magic bitboards in tests

* Rename bitboard operators +,* to |,&

* Added inline qualifiers

meson.build

@@ -435,6 +435,10 @@ if not get_option('popcnt')
   add_project_arguments('-DNO_POPCNT', language : 'cpp')
 endif
 
+if not get_option('pext')
+  add_project_arguments('-DNO_PEXT', language : 'cpp')
+endif
+
 executable('lc0', 'src/main.cc',
   files, include_directories: includes, dependencies: deps, install: true)
 

meson_options.txt

@@ -113,6 +113,11 @@ option('popcnt',
        value: true,
        description: 'Use the popcnt instruction')
 
+option('pext',
+       type: 'boolean',
+       value: false,
+       description: 'Use the pext instruction')
+
 option('gtest',
        type: 'boolean',
        value: true,

src/chess/bitboard.h

@@ -177,6 +177,10 @@ class BitBoard {
     return board_ == other.board_;
   }
 
+  bool operator!=(const BitBoard& other) const {
+    return board_ != other.board_;
+  }
+
   BitIterator<BoardSquare> begin() const { return board_; }
   BitIterator<BoardSquare> end() const { return 0; }
 
@@ -195,7 +199,7 @@ class BitBoard {
   }
 
   // Applies a mask to the bitboard (intersects).
-  BitBoard& operator*=(const BitBoard& a) {
+  BitBoard& operator&=(const BitBoard& a) {
     board_ &= a.board_;
     return *this;
   }
@@ -206,10 +210,15 @@ class BitBoard {
   }
 
   // Returns union (bitwise OR) of two boards.
-  friend BitBoard operator+(const BitBoard& a, const BitBoard& b) {
+  friend BitBoard operator|(const BitBoard& a, const BitBoard& b) {
     return {a.board_ | b.board_};
   }
 
+  // Returns intersection (bitwise AND) of two boards.
+  friend BitBoard operator&(const BitBoard& a, const BitBoard& b) {
+    return {a.board_ & b.board_};
+  }
+
   // Returns bitboard with one bit reset.
   friend BitBoard operator-(const BitBoard& a, const BoardSquare& b) {
     return {a.board_ & ~(1ULL << b.as_int())};
@@ -220,11 +229,6 @@ class BitBoard {
     return {a.board_ & ~b.board_};
   }
 
-  // Returns intersection (bitwise AND) of two boards.
-  friend BitBoard operator*(const BitBoard& a, const BitBoard& b) {
-    return {a.board_ & b.board_};
-  }
-
  private:
   std::uint64_t board_ = 0;
 };