refactor: separate bitboard functionality

5 files changed, 88 insertions, 62 deletions

diff --git a/src/bitboard.c b/src/bitboard.c
new file mode 100644
index 0000000..e9a7d53
--- /dev/null
+++ b/src/bitboard.c
@@ -0,0 +1,30 @@
+#include <stdio.h>
+#include "bitboard.h"
+
+/* Print bitboard on screen in the same way squares appear in memory
+ * (i.e the board is actually flipped along X) */
+void print_bitboard(Bitboard bb) {
+  for (U64 index = 0; index < 64; index++) {
+    printf("%lu", (bb >> index) & 1);
+    if ((index + 1) % 8 == 0) printf("\n");
+  }
+  printf("\n\n");
+}
+
+/* Return bitboard cardinality, aka number of elements in the set */
+inline int pop_count(Bitboard bb){
+  if (bb == 0) return 0;
+  return pop_count(bb >> 1) + (bb & 1);
+}
+
+/* Return Bitboard with only Least Single Bit */
+inline Bitboard ls1b(Bitboard bb) {
+  return bb & -bb;
+}
+
+/* Log base 2 (aka Trailing Zero Count)
+ * Only works for SINGLE Bitboards
+ * Useful for calculating bit-index of LS1B */
+inline Bitboard bitscan(Bitboard bb) {
+  return pop_count(ls1b(bb) - 1);
+}
diff --git a/src/bitboard.h b/src/bitboard.h
new file mode 100644
index 0000000..b90bd8f
--- /dev/null
+++ b/src/bitboard.h
@@ -0,0 +1,12 @@
+#include "types.h"
+
+typedef U64 Bitboard;
+#define BIT (U64)1
+
+int pop_count(Bitboard bb);
+
+void print_bitboard(Bitboard bb);
+
+Bitboard ls1b(Bitboard bb);
+
+Bitboard bitscan(Bitboard bb);
diff --git a/src/board.c b/src/board.c
index 0c133a8..d88c1ee 100644
--- a/src/board.c
+++ b/src/board.c
@@ -2,56 +2,6 @@
 #include <string.h>
 #include "board.h"
 
-int pop_count(Bitboard bb){
-  if (bb == 0) return 0;
-  return pop_count(bb >> 1) + (bb & 1);
-}
-
-void print_bitboard(Bitboard bb) {
-  for (U64 index = 0; index < 64; index++) {
-    printf("%lu", (bb >> index) & 1);
-    if ((index + 1) % 8 == 0) printf("\n");
-  }
-  printf("\n\n");
-}
-
-
-void precompute_knight_attack_table(Bitboard attacks[64]) {
-  for (int index = 0; index < 64; index++) {
-    U64 position = BIT << index;
-
-    attacks[index] =
-      ((position & notAFile & notBFile) << 6) |
-      ((position & notGFile & notHFile) << 10) |
-      ((position & notAFile) << 15) |
-      ((position & notHFile) << 17) |
-      ((position & notGFile & notHFile) >> 6) |
-      ((position & notAFile & notBFile) >> 10) |
-      ((position & notHFile) >> 15) |
-      ((position & notAFile) >> 17);
-  }
-}
-
-void precompute_king_attack_table(Bitboard attacks[64]) {
-  for (int index = 0; index < 64; index++) {
-    U64 position = BIT << index;
-
-    attacks[index] =
-      (position & notAFile) << 7 | (position << 8) | (position & notHFile) << 9 |
-      (position & notAFile) >> 1 |                   (position & notHFile) << 1 |
-      (position & notAFile) >> 9 | (position >> 8) | (position & notHFile) >> 7;
-  }
-}
-
-void precompute_pawn_attack_table(Bitboard attacks[64], BYTE color) {
-  for (int index = 0; index < 64; index++) {
-    U64 position = BIT << index;
-
-    if (color == WHITE) attacks[index] = (position & notAFile) << 7 | (position & notHFile) << 9;
-    else                attacks[index] = (position & notAFile) >> 9 | (position & notHFile) >> 7;
-  }
-}
-
 Board parse_FEN(char* FEN) {
   Board board;
   for (int i = 0; i < 12; i++) board.pieces[i] = 0;
@@ -138,3 +88,40 @@ void print_board(Board board) {
   }
   printf("  a b c d e f g h\n");
 }
+
+void precompute_knight_attack_table(Bitboard attacks[64]) {
+  for (int index = 0; index < 64; index++) {
+    U64 position = BIT << index;
+
+    attacks[index] =
+      ((position & notAFile & notBFile) << 6) |
+      ((position & notGFile & notHFile) << 10) |
+      ((position & notAFile) << 15) |
+      ((position & notHFile) << 17) |
+      ((position & notGFile & notHFile) >> 6) |
+      ((position & notAFile & notBFile) >> 10) |
+      ((position & notHFile) >> 15) |
+      ((position & notAFile) >> 17);
+  }
+}
+
+void precompute_king_attack_table(Bitboard attacks[64]) {
+  for (int index = 0; index < 64; index++) {
+    U64 position = BIT << index;
+
+    attacks[index] =
+      (position & notAFile) << 7 | (position << 8) | (position & notHFile) << 9 |
+      (position & notAFile) >> 1 |                   (position & notHFile) << 1 |
+      (position & notAFile) >> 9 | (position >> 8) | (position & notHFile) >> 7;
+  }
+}
+
+void precompute_pawn_attack_table(Bitboard attacks[64], BYTE color) {
+  for (int index = 0; index < 64; index++) {
+    U64 position = BIT << index;
+
+    if (color == WHITE) attacks[index] = (position & notAFile) << 7 | (position & notHFile) << 9;
+    else                attacks[index] = (position & notAFile) >> 9 | (position & notHFile) >> 7;
+  }
+}
+
diff --git a/src/board.h b/src/board.h
index cf89794..e3309e2 100644
--- a/src/board.h
+++ b/src/board.h
@@ -1,4 +1,4 @@
-#include "types.h"
+#include "bitboard.h"
 
 #define WHITE  0b0000
 #define BLACK  0b0001
@@ -10,9 +10,6 @@
 #define QUEEN  0b1000
 #define KING   0b1010
 
-typedef U64 Bitboard;
-#define BIT (U64)1
-
 typedef struct {
   Bitboard pieces[12];
   BYTE side;
@@ -31,11 +28,6 @@ enum enumSquare {
   a8, b8, c8, d8, e8, f8, g8, h8
 };
 
-#define notAFile 0xFEFEFEFEFEFEFEFE
-#define notBFile 0xFDFDFDFDFDFDFDFD
-#define notGFile 0xBFBFBFBFBFBFBFBF
-#define notHFile 0x7F7F7F7F7F7F7F7F
-
 static const char* notation[64] = {
   "a1", "b1", "c1", "d1", "e1", "f1", "g1", "h1",
   "a2", "b2", "c2", "d2", "e2", "f2", "g2", "h2",
@@ -56,11 +48,15 @@ static const char* pieces[] = {
   "♚", "♔",
 };
 
-void print_bitboard(Bitboard bb);
-int pop_count(Bitboard bb);
-void print_board(Board board);
+#define notAFile 0xFEFEFEFEFEFEFEFE
+#define notBFile 0xFDFDFDFDFDFDFDFD
+#define notGFile 0xBFBFBFBFBFBFBFBF
+#define notHFile 0x7F7F7F7F7F7F7F7F
+
 Board parse_FEN(char* FEN);
 
+void print_board(Board board);
+
 void precompute_knight_attack_table(Bitboard table[64]);
 void precompute_king_attack_table(Bitboard table[64]);
 void precompute_pawn_attack_table(Bitboard table[64], BYTE color);
diff --git a/src/main.c b/src/main.c
index d6aa2b8..2bd9583 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,5 +1,6 @@
 #include "unittest.h"
 #include "board.h"
+#include "bitboard.h"
 
 int main() {
   start_test_section("Bitboards"); {