feat: compute knight attack table

4 files changed, 81 insertions, 17 deletions

diff --git a/src/board.c b/src/board.c
index bc5855f..59b6043 100644
--- a/src/board.c
+++ b/src/board.c
@@ -1,10 +1,32 @@
+#include <stdio.h>
 #include "board.h"
 
-BYTE notation_to_index(char file, int rank) {
-  return (rank - 1) * 8 + (file - 'a');
+int pop_count(Bitboard bb){
+  if (bb == 0) return 0;
+  return pop_count(bb >> 1) + (bb & 1);
 }
 
-void index_to_notation(BYTE index, char notation[2]) {
-  notation[0] = (index & 0b0111) + 'a';
-  notation[1] = (index >> 3) + '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 = (U64)1 << 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);
+  }
 }
diff --git a/src/board.h b/src/board.h
index f7e89f2..154878c 100644
--- a/src/board.h
+++ b/src/board.h
@@ -10,7 +10,7 @@
 #define QUEEN  0b1000
 #define KING   0b1010
 
-typedef QWORD Bitboard;
+typedef U64 Bitboard;
 
 typedef struct {
   Bitboard pieces[12];
@@ -19,6 +19,33 @@ typedef struct {
   BYTE en_passant_square;
 } Board;
 
+enum enumSquare {
+  a1, b1, c1, d1, e1, f1, g1, h1,
+  a2, b2, c2, d2, e2, f2, g2, h2,
+  a3, b3, c3, d3, e3, f3, g3, h3,
+  a4, b4, c4, d4, e4, f4, g4, h4,
+  a5, b5, c5, d5, e5, f5, g5, h5,
+  a6, b6, c6, d6, e6, f6, g6, h6,
+  a7, b7, c7, d7, e7, f7, g7, h7,
+  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",
+  "a3", "b3", "c3", "d3", "e3", "f3", "g3", "h3",
+  "a4", "b4", "c4", "d4", "e4", "f4", "g4", "h4",
+  "a5", "b5", "c5", "d5", "e5", "f5", "g5", "h5",
+  "a6", "b6", "c6", "d6", "e6", "f6", "g6", "h6",
+  "a7", "b7", "c7", "d7", "e7", "f7", "g7", "h7",
+  "a8", "b8", "c8", "d8", "e8", "f8", "g8", "h8"
+};
+
 static const char* pieces[] = {
   "♟︎", "♙",
   "♞", "♘",
@@ -28,5 +55,6 @@ static const char* pieces[] = {
   "♚", "♔",
 };
 
-void index_to_notation(BYTE index, char notation[2]);
-BYTE notation_to_index(char file, int rank);
+void precompute_knight_attack_table();
+void print_bitboard(Bitboard bb);
+int pop_count(Bitboard bb);
diff --git a/src/main.c b/src/main.c
index 75d3bb7..2e95970 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,17 +1,30 @@
 #include "unittest.h"
 #include "board.h"
 
-void test_notations() {
-  printf("%u\n", notation_to_index('e', 4));
-  unit_test(notation_to_index('e', 4) == 28, "Notation e4 is index 28");
+int main() {
+  { // Pop count
+    unit_test(pop_count(0b01110) == 3, "Pop count of 01110 is 3");
+  }
 
-  char notation[2] = "x0";
-  index_to_notation(28, notation);
-  unit_test(notation[0] == 'e' && notation [1] == '4', "Index 28 is notation e4");
-}
+  { // Test knight attacks
+    Bitboard attacks[64];
+    precompute_knight_attack_table(attacks);
 
-int main() {
-  test_notations();
+    int max_attacks = 0;
+    for (int i = 0; i < 64; i++) {
+      int attack_count = pop_count(attacks[i]);
+      if (attack_count > max_attacks) max_attacks = attack_count;
+    }
+    unit_test(max_attacks == 8, "Max amount of knight attacks should be 8");
+
+    { // Knight on b7 attack table
+      U64 bit = 1;
+      unit_test(
+          attacks[b7] == ((bit << d8) | (bit << d6) | (bit << c5) | (bit << a5)),
+          "Knight on b7 attacks d8, d6, c5, a5"
+      );
+    }
+  }
 
   report();
   return 0;
diff --git a/src/types.h b/src/types.h
index 4f95bb3..371d8b8 100644
--- a/src/types.h
+++ b/src/types.h
@@ -1,5 +1,6 @@
 typedef unsigned char  BYTE;
 typedef unsigned short WORD;
 typedef unsigned long QWORD;
+typedef unsigned long U64;