add-fen-loader (#5)

Reviewed-on: #5
Co-authored-by: Josh <josh@joshuaschuett.com>
Co-committed-by: Josh <josh@joshuaschuett.com>

engine/src/bitboard.c

@@ -1,4 +1,5 @@
 #include "bitboard.h"
+#include <stdio.h>
 
 uint64_t PAWN_ATTACKS[2][64];
 uint64_t KNIGHT_ATTACKS[64];
@@ -58,4 +59,45 @@ void create_king_attack_cache(void) {
 
         KING_ATTACKS[sq] = mask;
     }
+}
+
+static int first_set_index(uint64_t bb) {
+    for (int i = 0; i < 64; ++i) {
+        if ((bb >> i) & 1ULL) return i;
+    }
+    return -1;
+}
+
+static int pop_lsb_index(uint64_t *bb) {
+    if (*bb == 0) return -1;
+    int idx = first_set_index(*bb);
+    // Clears bit.
+    *bb &= ~(1ULL << idx);
+    return idx;
+}
+
+void print_board(const struct Board *b) {
+    static const char PIECE_CH[12] = {
+        'P','N','B','R','Q','K',
+        'p','n','b','r','q','k'
+    };
+
+    char grid[64];
+    for (int i = 0; i < 64; ++i) grid[i] = '.';
+
+    for (int p = 0; p < 12; ++p) {
+        uint64_t bb = b->pieces[p];
+        while (bb) {
+            int sq = pop_lsb_index(&bb);
+            grid[sq] = PIECE_CH[p];
+        }
+    }
+
+    for (int r = 7; r >= 0; --r) {
+        for (int f = 0; f < 8; ++f) {
+            putchar(grid[r * 8 + f]);
+            if (f < 7) putchar(' ');
+        }
+        putchar('\n');
+    }
 }