Add Pseudo Move Generator (#12)

work on #7

Reviewed-on: #12
Co-authored-by: Josh <josh@joshuaschuett.com>
Co-committed-by: Josh <josh@joshuaschuett.com>

engine/src/bitboard.c

@@ -61,14 +61,14 @@ void create_king_attack_cache(void) {
     }
 }
 
-static int first_set_index(uint64_t bb) {
+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) {
+int pop_lsb_index(uint64_t *bb) {
     if (*bb == 0) return -1;
     int idx = first_set_index(*bb);
     // Clears bit.
@@ -76,8 +76,463 @@ static int pop_lsb_index(uint64_t *bb) {
     return idx;
 }
 
-void print_board(const struct Board *b) {
-    static const char PIECE_CH[12] = {
+uint64_t ray_attacks(int start_square, int delta_file, int delta_rank, uint64_t occupied)
+{
+    uint64_t attacks = 0;
+
+    int start_file = start_square % 8;
+    int start_rank = start_square / 8;
+
+    int next_file = start_file + delta_file;
+    int next_rank = start_rank + delta_rank;
+
+    while (next_file >= 0 && next_file < 8 && next_rank >= 0 && next_rank < 8) {
+        int next_square = next_rank * 8 + next_file;
+        uint64_t next_bit = 1ULL << next_square;
+
+        // can attack this square
+        attacks |= next_bit;
+
+        // blocker: include it, then stop
+        if (occupied & next_bit)
+            break;
+
+        next_file += delta_file;
+        next_rank += delta_rank;
+    }
+
+    return attacks;
+}
+
+uint64_t rook_attacks(int square, uint64_t occupied) {
+    return  ray_attacks(square, +1,  0, occupied)   // east
+          | ray_attacks(square, -1,  0, occupied)   // west
+          | ray_attacks(square,  0, +1, occupied)   // north
+          | ray_attacks(square,  0, -1, occupied);  // south
+}
+
+uint64_t bishop_attacks(int square, uint64_t occupied) {
+    return  ray_attacks(square, +1, +1, occupied)   // NE
+          | ray_attacks(square, -1, +1, occupied)   // NW
+          | ray_attacks(square, +1, -1, occupied)   // SE
+          | ray_attacks(square, -1, -1, occupied);  // SW
+}
+
+uint64_t queen_attacks(int square, uint64_t occupied) {
+    // Simply combine both types of attacks
+    return rook_attacks(square, occupied) | bishop_attacks(square, occupied);
+}
+
+void push_move(struct Move *out, int *count, int from, int to, uint8_t piece, uint8_t promo, uint8_t flags)
+{
+    out[*count] = (struct Move){
+        .from  = (uint16_t)from,
+        .to    = (uint16_t)to,
+        .piece = piece,
+        .promo = promo,    // 0 for non-promo;
+        .flags = flags
+    };
+    (*count)++;
+}
+
+/**
+    PAWN struct Movement Psuedo Moves
+
+
+    Separate the white and black pawn logic. Although the logic is similar,
+    by separating the logic, we can isolate the different cases and have clearer parent functions.
+    These pieces are also the only ones that move in opposite ways, meaning we only need
+    to separate out seemingly related code for this case. Additionally, pawns have the
+    most complicated movement patterns and behaviors in the game. Separating out the logic should
+    hopefully make debugging easier.
+*/
+void gen_white_pawn_quiet_pushes(const struct Board *board, struct Move *out, int *count) {
+    const uint64_t occ   = board->occ[BOTH];
+    const uint64_t empty = ~occ;
+
+    const uint64_t pawns = board->pieces[P];
+
+    // One-step pushes: shift pawns up by 8 onto empty squares
+    uint64_t one_step = (pawns << 8) & empty;
+
+    // Exclude promotions here (dest on rank 8) — handled by a separate promo-push function
+    uint64_t one_step_no_promo = one_step & ~RANK_8;
+
+    // Two-step pushes: those one-step pawns that landed on rank 3 can go one more if still empty
+    // (means they originally stood on rank 2)
+    uint64_t two_step = ((one_step & RANK_3) << 8) & empty;
+
+    uint64_t bb = one_step_no_promo;
+    while (bb) {
+        int to = pop_lsb_index(&bb);
+        int from = to - 8;
+        push_move(out, count, from, to, P, 0, MF_NONE);
+    }
+
+    bb = two_step;
+    while (bb) {
+        int to = pop_lsb_index(&bb);
+        int from = to - 16;
+        push_move(out, count, from, to, P, 0, MF_DOUBLE_PUSH);
+    }
+}
+
+void gen_black_pawn_quiet_pushes(const struct Board *board, struct Move *out, int *count) {
+    const uint64_t occ   = board->occ[BOTH];
+    const uint64_t empty = ~occ;
+
+    const uint64_t pawns = board->pieces[p];
+
+    // One-step pushes: shift pawns down by 8 onto empty squares
+    uint64_t one_step = (pawns >> 8) & empty;
+
+    // Exclude promotions here (dest on rank 1) — handle in a promo-push function
+    uint64_t one_step_no_promo = one_step & ~RANK_1;
+
+    uint64_t two_step = ((one_step & RANK_6) >> 8) & empty;
+
+    uint64_t bb = one_step_no_promo;
+    while (bb) {
+        int to   = pop_lsb_index(&bb);
+        int from = to + 8;
+        push_move(out, count,from, to, p, 0, MF_NONE);
+    }
+
+    bb = two_step;
+    while (bb) {
+        int to   = pop_lsb_index(&bb);
+        int from = to + 16;
+        push_move(out, count,from, to, p, 0, MF_DOUBLE_PUSH);
+    }
+}
+
+// We will only allow pawns to promote to queen. Technically, they should be allowed
+// to promote to any of the following: Rook, Bishop, Knight, Queen.
+void gen_white_pawn_push_promotions(const struct Board *board, struct Move *out, int *count) {
+    const uint64_t occ   = board->occ[BOTH];
+    const uint64_t empty = ~occ;
+    const uint64_t pawns = board->pieces[P];
+
+    // destinations on rank 8 reachable by a single push
+    uint64_t promos = ((pawns << 8) & empty) & RANK_8;
+
+    while (promos) {
+        int to   = pop_lsb_index(&promos);
+        int from = to - 8;
+        push_move(out, count, from, to, P, Q, MF_PROMO);
+    }
+}
+
+void gen_black_pawn_push_promotions(const struct Board *board, struct Move *out, int *count) {
+    const uint64_t occ   = board->occ[BOTH];
+    const uint64_t empty = ~occ;
+    const uint64_t pawns = board->pieces[p];
+
+    // destinations on rank 1 reachable by a single push
+    uint64_t promos = ((pawns >> 8) & empty) & RANK_1;
+
+    while (promos) {
+        int to   = pop_lsb_index(&promos);
+        int from = to + 8;
+        push_move(out, count, from, to, p, q, MF_PROMO);
+    }
+}
+
+void gen_white_pawn_capture_promotions(const struct Board *board, struct Move *out, int *count) {
+    const uint64_t opp = board->occ[BLACK];
+    // left capture (from white view): +7, mask off file A
+    uint64_t left  = ((board->pieces[P] & ~FILE_A) << 7) & opp & RANK_8;
+    while (left) {
+        int to = pop_lsb_index(&left);
+        int from = to - 7;
+        push_move(out, count,from, to, P, Q, MF_CAPTURE | MF_PROMO);
+    }
+    // right capture: +9, mask off file H
+    uint64_t right = ((board->pieces[P] & ~FILE_H) << 9) & opp & RANK_8;
+    while (right) {
+        int to = pop_lsb_index(&right);
+        int from = to - 9;
+        push_move(out, count,from, to, P, Q, MF_CAPTURE | MF_PROMO);
+    }
+}
+
+void gen_black_pawn_capture_promotions(const struct Board *board, struct Move *out, int *count) {
+    const uint64_t opp = board->occ[WHITE];
+    // from black view, “left” is -7 (mask off file H before shifting)
+    uint64_t left  = ((board->pieces[p] & ~FILE_H) >> 7) & opp & RANK_1;
+    while (left) {
+        int to = pop_lsb_index(&left);
+        int from = to + 7;
+        push_move(out, count,from, to, p, q, MF_CAPTURE | MF_PROMO);
+    }
+    // “right” is -9 (mask off file A)
+    uint64_t right = ((board->pieces[p] & ~FILE_A) >> 9) & opp & RANK_1;
+    while (right) {
+        int to = pop_lsb_index(&right);
+        int from = to + 9;
+        push_move(out, count,from, to, p, q, MF_CAPTURE | MF_PROMO);
+    }
+}
+
+void gen_white_pawn_captures(const struct Board *board, struct Move *out, int *count) {
+    const uint64_t pawns  = board->pieces[P];
+    const uint64_t opp    = board->occ[BLACK];
+
+    // Normal captures (exclude promotion rank)
+    uint64_t left_caps  = ((pawns & ~FILE_A) << 7) & opp & ~RANK_8;
+    uint64_t right_caps = ((pawns & ~FILE_H) << 9) & opp & ~RANK_8;
+
+    // Emit normal captures
+    while (left_caps) {
+        int to   = pop_lsb_index(&left_caps);
+        int from = to - 7;
+        push_move(out, count,from, to, P, 0, MF_CAPTURE);
+    }
+    while (right_caps) {
+        int to   = pop_lsb_index(&right_caps);
+        int from = to - 9;
+        push_move(out, count,from, to, P, 0, MF_CAPTURE);
+    }
+
+    // En passant (destination is ep_square)
+    if (board->ep_square >= 0) {
+        uint64_t ep = 1ULL << board->ep_square;
+
+        // From-squares that can capture onto ep (reverse of +7/+9)
+        uint64_t ep_from = (((ep & ~FILE_H) >> 7) | ((ep & ~FILE_A) >> 9)) & pawns;
+
+        while (ep_from) {
+            int from = pop_lsb_index(&ep_from);
+            int to   = board->ep_square;
+            // EP never promotes, so no promo piece; still a capture
+            push_move(out, count,from, to, P, 0, MF_CAPTURE | MF_ENPASSANT);
+        }
+    }
+}
+
+void gen_black_pawn_captures(const struct Board *board, struct Move *out, int *count) {
+    const uint64_t pawns  = board->pieces[p];
+    const uint64_t opp    = board->occ[WHITE];
+
+    // Normal captures (exclude promotion rank)
+    uint64_t left_caps  = ((pawns & ~FILE_H) >> 7) & opp & ~RANK_1; // from black POV, "left" is -7
+    uint64_t right_caps = ((pawns & ~FILE_A) >> 9) & opp & ~RANK_1; // "right" is -9
+
+    while (left_caps) {
+        int to   = pop_lsb_index(&left_caps);
+        int from = to + 7;
+        push_move(out, count,from, to, p, 0, MF_CAPTURE);
+    }
+    while (right_caps) {
+        int to   = pop_lsb_index(&right_caps);
+        int from = to + 9;
+        push_move(out, count,from, to, p, 0, MF_CAPTURE);
+    }
+
+    // En passant
+    if (board->ep_square >= 0) {
+        uint64_t ep = 1ULL << board->ep_square;
+
+        // From-squares that can capture onto ep (reverse of -7/-9)
+        uint64_t ep_from = (((ep & ~FILE_A) << 7) | ((ep & ~FILE_H) << 9)) & pawns;
+
+        while (ep_from) {
+            int from = pop_lsb_index(&ep_from);
+            int to   = board->ep_square;
+            push_move(out, count,from, to, p, 0, MF_CAPTURE | MF_ENPASSANT);
+        }
+    }
+}
+
+/**
+
+
+    Pieces that are not PAWNs
+
+
+*/
+void gen_knight_moves(const struct Board *board, struct Move *out, int *count, bool captures_only) {
+    enum Color side = board->side_to_move;
+    uint64_t own = board->occ[side];
+    uint64_t opp = board->occ[side ^ 1];
+    uint8_t pid = (side == WHITE) ? N : n;
+    uint64_t bb = (side == WHITE) ? board->pieces[N] : board->pieces[n];
+
+    while (bb) {
+        int from = pop_lsb_index(&bb);
+        uint64_t mask = KNIGHT_ATTACKS[from] & ~own;
+        uint64_t caps = mask & opp;
+
+        if (!captures_only) {
+            uint64_t quiet = mask & ~opp;
+            while (quiet) {
+                int to = pop_lsb_index(&quiet);
+                push_move(out, count, from, to, pid, 0, MF_NONE);
+            }
+        }
+        while (caps) {
+            int to = pop_lsb_index(&caps);
+            push_move(out, count, from, to, pid, 0, MF_CAPTURE);
+        }
+    }
+}
+
+void gen_bishop_moves(const struct Board *board, struct Move *out, int *count, bool captures_only) {
+    enum Color side = board->side_to_move;
+    uint64_t own = board->occ[side];
+    uint64_t opp = board->occ[side ^ 1];
+    uint64_t occ = board->occ[BOTH];
+    uint8_t pid = (side == WHITE) ? B : b;
+    uint64_t bb = (side == WHITE) ? board->pieces[B] : board->pieces[b];
+
+    while (bb) {
+        int from = pop_lsb_index(&bb);
+        uint64_t mask = bishop_attacks(from, occ) & ~own;
+        uint64_t caps = mask & opp;
+
+        if (!captures_only) {
+            uint64_t quiet = mask & ~opp;
+            while (quiet) {
+                int to = pop_lsb_index(&quiet);
+                push_move(out, count, from, to, pid, 0, MF_NONE);
+            }
+        }
+        while (caps) {
+            int to = pop_lsb_index(&caps);
+            push_move(out, count, from, to, pid, 0, MF_CAPTURE);
+        }
+    }
+}
+
+void gen_rook_moves(const struct Board *board, struct Move *out, int *count, bool captures_only) {
+    enum Color side = board->side_to_move;
+    uint64_t own = board->occ[side];
+    uint64_t opp = board->occ[side ^ 1];
+    uint64_t occ = board->occ[BOTH];
+    uint8_t pid = (side == WHITE) ? R : r;
+    uint64_t bb = (side == WHITE) ? board->pieces[R] : board->pieces[r];
+
+    while (bb) {
+        int from = pop_lsb_index(&bb);
+        uint64_t mask = rook_attacks(from, occ) & ~own;
+        uint64_t caps = mask & opp;
+
+        if (!captures_only) {
+            uint64_t quiet = mask & ~opp;
+            while (quiet) {
+                int to = pop_lsb_index(&quiet);
+                push_move(out, count,from, to, pid, 0, MF_NONE);
+            }
+        }
+        while (caps) {
+            int to = pop_lsb_index(&caps);
+            push_move(out, count,from, to, pid, 0, MF_CAPTURE);
+        }
+    }
+}
+
+void gen_queen_moves(const struct Board *board, struct Move *out, int *count, bool captures_only) {
+    enum Color side = board->side_to_move;
+    uint64_t own = board->occ[side];
+    uint64_t opp = board->occ[side ^ 1];
+    uint64_t occ = board->occ[BOTH];
+    uint8_t pid = (side == WHITE) ? Q : q;
+    uint64_t bb = (side == WHITE) ? board->pieces[Q] : board->pieces[q];
+
+    while (bb) {
+        int from = pop_lsb_index(&bb);
+        uint64_t mask = (rook_attacks(from, occ) | bishop_attacks(from, occ)) & ~own;
+        uint64_t caps = mask & opp;
+
+        if (!captures_only) {
+            uint64_t quiet = mask & ~opp;
+            while (quiet) {
+                int to = pop_lsb_index(&quiet);
+                push_move(out, count,from, to, pid, 0, MF_NONE);
+            }
+        }
+        while (caps) {
+            int to = pop_lsb_index(&caps);
+            push_move(out, count,from, to, pid, 0, MF_CAPTURE);
+        }
+    }
+}
+
+void gen_king_moves(const struct Board *board, struct Move *out, int *count, bool captures_only) {
+    enum Color side = board->side_to_move;
+    uint64_t own = board->occ[side];
+    uint64_t opp = board->occ[side ^ 1];
+    uint8_t pid = (side == WHITE) ? K : k;
+    uint64_t kk = (side == WHITE) ? board->pieces[K] : board->pieces[k];
+
+    if (!kk) return;
+    int from = first_set_index(kk);
+    uint64_t mask = KING_ATTACKS[from] & ~own;
+    uint64_t caps = mask & opp;
+
+    if (!captures_only) {
+        uint64_t quiet = mask & ~opp;
+        while (quiet) {
+            int to = pop_lsb_index(&quiet);
+            push_move(out, count,from, to, pid, 0, MF_NONE);
+        }
+    }
+    while (caps) {
+        int to = pop_lsb_index(&caps);
+        push_move(out, count,from, to, pid, 0, MF_CAPTURE);
+    }
+
+    if (!captures_only) {
+        uint64_t occ = board->occ[BOTH];
+        if (side == WHITE) {
+            if ((board->castling_rights & CASTLE_WK) && !(occ & WK_EMPTY_MASK)) {
+                push_move(out, count,E1, WK_TO, K, 0, MF_CASTLE);
+            }
+            if ((board->castling_rights & CASTLE_WQ) && !(occ & WQ_EMPTY_MASK)) {
+                push_move(out, count,E1, WQ_TO, K, 0, MF_CASTLE);
+            }
+        } else {
+            if ((board->castling_rights & CASTLE_BK) && !(occ & BK_EMPTY_MASK)) {
+                push_move(out, count,E8, BK_TO, k, 0, MF_CASTLE);
+            }
+            if ((board->castling_rights & CASTLE_BQ) && !(occ & BQ_EMPTY_MASK)) {
+                push_move(out, count,E8, BQ_TO, k, 0, MF_CASTLE);
+            }
+        }
+    }
+}
+
+int gen_pseudo_moves(const struct Board *board, struct Move *moves, bool captures_only) {
+    int count = 0;
+
+    if (board->side_to_move == WHITE) {
+        if (!captures_only) {
+            gen_white_pawn_quiet_pushes(board, moves, &count);
+            gen_white_pawn_push_promotions(board, moves, &count);
+        }
+        gen_white_pawn_captures(board, moves, &count);
+        gen_white_pawn_capture_promotions(board, moves, &count);
+    } else {
+        if (!captures_only) {
+            gen_black_pawn_quiet_pushes(board, moves, &count);
+            gen_black_pawn_push_promotions(board, moves, &count);
+        }
+        gen_black_pawn_captures(board, moves, &count);
+        gen_black_pawn_capture_promotions(board, moves, &count);
+    }
+
+    gen_knight_moves(board, moves, &count, captures_only);
+    gen_king_moves(board, moves, &count, captures_only);
+    gen_rook_moves(board, moves, &count, captures_only);
+    gen_bishop_moves(board, moves, &count, captures_only);
+    gen_queen_moves(board, moves, &count, captures_only);
+
+    return count;
+}
+
+
+void print_board(const struct Board *board) {
+    const char PIECE_CH[12] = {
         'P','N','B','R','Q','K',
         'p','n','b','r','q','k'
     };
@@ -86,7 +541,7 @@ void print_board(const struct Board *b) {
     for (int i = 0; i < 64; ++i) grid[i] = '.';
 
     for (int p = 0; p < 12; ++p) {
-        uint64_t bb = b->pieces[p];
+        uint64_t bb = board->pieces[p];
         while (bb) {
             int sq = pop_lsb_index(&bb);
             grid[sq] = PIECE_CH[p];

engine/src/test.c

@@ -1,33 +1,116 @@
-/**
-    A quick test script to debug and visually inspect functions
-    and operations.
-*/
-
-
+// engine/src/test_pawns.c
 #include <stdio.h>
 #include <string.h>
 #include "bitboard.h"
 #include "fen.h"
 
+enum { MAX_MOVES = 256 };
 
-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'};
+void sq_to_coord(int sq, char out[3]) {
+    out[0] = 'a' + (sq % 8);
+    out[1] = '1' + (sq / 8);
+    out[2] = '\0';
+}
 
+void print_move(struct Move *m) {
+    char f[3], t[3];
+    sq_to_coord(m->from, f);
+    sq_to_coord(m->to,   t);
+
+    printf("%s%s", f, t);
+    if (m->flags) {
+        printf(" [");
+        int first = 1;
+        if (m->flags & MF_CAPTURE)     { printf("%sCAP", first?"":"|"); first = 0; }
+        if (m->flags & MF_DOUBLE_PUSH) { printf("%sDP",  first?"":"|"); first = 0; }
+        if (m->flags & MF_ENPASSANT)   { printf("%sEP",  first?"":"|"); first = 0; }
+        if (m->flags & MF_PROMO)       { printf("%sPROMO->%c", first?"":"|", (char)(m->promo ? "PNBRQKpnbrqk"[m->promo] : 'Q')); }
+        printf("]");
+    }
+}
+
+void dump_moves(const char *title, struct Move *moves, int count) {
+    printf("%s (%d):\n", title, count);
+    for (int i = 0; i < count; ++i) { print_move(&moves[i]); putchar('\n'); }
+    putchar('\n');
+}
 
 int main(void) {
-    const char *fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
+    // change this FEN to target specific cases you want to test
+    //const char *fen_startpos = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
+    const char *fen_startpos = "8/8/8/8/8/8/8/8 w KQkq - 0 1";
+    const char *fen = fen_startpos;
 
     struct Board b;
+    memset(&b, 0, sizeof(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);
+    if (load_fen(&b, fen) != 0) {
+        fprintf(stderr, "load_fen failed\n");
         return 1;
     }
 
-    print_board(&b);
+    struct Move moves[MAX_MOVES];
+    int count;
+
+    /*
+    // --- WHITE pawns: quiet pushes (single + double, no promos) ---
+    count = 0;
+    gen_white_pawn_quiet_pushes(&b, moves, &count);
+    dump_moves("white quiet pushes", moves, count);
+
+
+    // --- BLACK pawns: quiet pushes ---
+    gen_black_pawn_quiet_pushes(&b, moves, &count);
+    dump_moves("black quiet pushes", moves, count);
+
+    printf("COUNT: %d", count);
+    */
+    
+    create_knight_attack_cache();
+    //create_king_attack_cache();
+    //create_pawn_attack_cache();
+
+    int n = gen_pseudo_moves(&b, moves, false);
+    printf("COUNT: %d", n);
+
+    /*
+    // --- WHITE pawns: quiet push promotions (queen-only) ---
+    count = 0;
+    gen_white_pawn_push_promotions_q(&b, moves, &count);
+    dump_moves("white push promotions (Q only)", moves, count);
+
+    // --- WHITE pawns: captures (non-promo) + en passant ---
+    count = 0;
+    gen_white_pawn_captures(&b, moves, &count);
+    dump_moves("white captures (non-promo + EP)", moves, count);
+
+    // --- WHITE pawns: capture promotions (queen-only) ---
+    count = 0;
+    gen_white_pawn_capture_promotions_q(&b, moves, &count);
+    dump_moves("white capture promotions (Q only)", moves, count);
+
+    // Flip side to move if you want to test black without changing FEN side
+    b.side_to_move = BLACK;
+
+    // --- BLACK pawns: quiet pushes ---
+    count = 0;
+    gen_black_pawn_quiet_pushes(&b, moves, &count);
+    dump_moves("black quiet pushes", moves, count);
+
+    // --- BLACK pawns: quiet push promotions (queen-only) ---
+    count = 0;
+    gen_black_pawn_push_promotions_q(&b, moves, &count);
+    dump_moves("black push promotions (q only)", moves, count);
+
+    // --- BLACK pawns: captures (non-promo) + en passant ---
+    count = 0;
+    gen_black_pawn_captures(&b, moves, &count);
+    dump_moves("black captures (non-promo + EP)", moves, count);
+
+    // --- BLACK pawns: capture promotions (queen-only) ---
+    count = 0;
+    gen_black_pawn_capture_promotions_q(&b, moves, &count);
+    dump_moves("black capture promotions (q only)", moves, count);
+    */
     return 0;
-}
+}