engine/include/bitboard.h

@@ -52,6 +52,7 @@ struct Board {
     int fullmove_number;
 };
 
-void create_knight_attack_cache(void);
+void create_knight_attack_cache();
-void create_pawn_attack_cache(void);
+void create_pawn_attack_cache();
-void create_king_attack_cache(void);
+void create_king_attack_cache();
+void print_board();

engine/include/fen.h

@@ -0,0 +1 @@
+int load_fen();

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');
+    }
 }

engine/src/fen.c

@@ -21,6 +21,10 @@ int char_to_piece_index(char c) {
 }
 
 int load_fen(struct Board *board, const char *fen) {
+    // Reset the board first. Weird behavior when not zeroed.
+    memset(board, 0, sizeof *board);
+    board->ep_square = -1;
+
     int rank = 7, file = 0;
     const char *ptr = fen;
 

engine/src/test.c

@@ -0,0 +1,33 @@
+/**
+    A quick test script to debug and visually inspect functions
+    and operations.
+*/
+
+
+#include <stdio.h>
+#include <string.h>
+#include "bitboard.h"
+#include "fen.h"
+
+
+static int popcount64(uint64_t x){ int c=0; while(x){ x&=x-1; ++c; } return c; }
+static const char NAME[12] = {'P','N','B','R','Q','K','p','n','b','r','q','k'};
+
+
+int main(void) {
+    const char *fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
+
+    struct Board b;
+
+    int rc = load_fen(&b, fen);
+
+    for (int i=0;i<12;i++) printf("%c: %d\n", NAME[i], popcount64(b.pieces[i]));
+
+    if (rc != 0) {
+        fprintf(stderr, "load_fen failed (rc=%d) for FEN:\n%s\n", rc, fen);
+        return 1;
+    }
+
+    print_board(&b);
+    return 0;
+}

makefile

@@ -7,11 +7,17 @@ INCDIR   := engine/include
 BUILDDIR := build
 LIBNAME  := libchess
 
-SRC := $(wildcard $(SRCDIR)/*.c)
+# Exclude test.c from the shared lib build
+SRC := $(filter-out $(SRCDIR)/test.c,$(wildcard $(SRCDIR)/*.c))
 OBJ := $(patsubst $(SRCDIR)/%.c,$(BUILDDIR)/%.o,$(SRC))
 LIB := $(BUILDDIR)/$(LIBNAME).so
 
-.PHONY: all clean test
+# ---- test executable (engine/src/test.c) ----
+TESTSRC := $(SRCDIR)/test.c
+TESTOBJ := $(BUILDDIR)/test.o
+TESTBIN := $(BUILDDIR)/print_board
+
+.PHONY: all clean test test-exe run
 
 all: $(LIB)
 
@@ -24,6 +30,17 @@ $(BUILDDIR)/%.o: $(SRCDIR)/%.c | $(BUILDDIR)
 $(LIB): $(OBJ)
 	$(CC) $(LDFLAGS) -o $@ $^
 
+c-test-exe: $(TESTBIN)
+
+$(TESTOBJ): $(TESTSRC) | $(BUILDDIR)
+	$(CC) -std=c11 -Wall -Wextra -O2 -I$(INCDIR) -c $< -o $@
+
+$(TESTBIN): $(TESTOBJ) $(LIB)
+	$(CC) -O2 -o $@ $(TESTOBJ) -L$(BUILDDIR) -lchess -Wl,-rpath,'$$ORIGIN'
+
+run-c-test: test-exe
+	LD_LIBRARY_PATH=$(BUILDDIR) $(TESTBIN) $(FEN)
+
 clean:
 	@echo "Cleaning build and Python caches..."
 	@rm -rf $(BUILDDIR)
@@ -31,7 +48,6 @@ clean:
 	@find . -type d -name ".pytest_cache"  -exec rm -rf {} +
 	@find . -type f \( -name "*.pyc" -o -name "*.pyo" \) -delete
 
-# Always rebuild, and always clean afterward (even if tests fail)
 test:
 	@$(MAKE) clean
 	@$(MAKE) all