From 2c2a70b69869f149c0407a62f1bf4c39899027a7 Mon Sep 17 00:00:00 2001
From: Aargh Rai <aargh.rai+git@gmail.com>
Date: Wed, 27 May 2026 18:02:44 +0530
Subject: restructing

---
 src/engine/moves/pawn.c | 164 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 164 insertions(+)
 create mode 100644 src/engine/moves/pawn.c

(limited to 'src/engine/moves/pawn.c')

diff --git a/src/engine/moves/pawn.c b/src/engine/moves/pawn.c
new file mode 100644
index 0000000..3cd28b8
--- /dev/null
+++ b/src/engine/moves/pawn.c
@@ -0,0 +1,164 @@
+#include "../moves.h"
+
+bitboard_t get_white_pawn_forwardmoves(moves_t* moves, position_t position) {
+  bitboard_t enemy_bitboard = blacks(position);
+  bitboard_t friendly_pieces =
+    position.bitboards[WHITE_KING] |
+    position.bitboards[WHITE_QUEEN] |
+    position.bitboards[WHITE_ROOK] |
+    position.bitboards[WHITE_BISHOP] |
+    position.bitboards[WHITE_KNIGHT] |
+    position.bitboards[WHITE_PAWN];
+  bitboard_t friendly_pawns = position.bitboards[WHITE_PAWN];
+  bitboard_t y = friendly_pieces | enemy_bitboard;
+  bitboard_t x = ~((friendly_pawns << 8) & y) & (friendly_pawns << 8);
+  bitboard_t first_move_x = x & BITMASK_RANK_3;
+
+  first_move_x |= (first_move_x << 8) & (~y);
+  x |= first_move_x;
+
+  return x;
+}
+bitboard_t get_black_pawn_forwardmoves(moves_t* moves, position_t position) {
+  bitboard_t enemy_bitboard = whites(position);
+  bitboard_t friendly_pieces =
+    position.bitboards[BLACK_KING] |
+    position.bitboards[BLACK_QUEEN] |
+    position.bitboards[BLACK_ROOK] |
+    position.bitboards[BLACK_BISHOP] |
+    position.bitboards[BLACK_KNIGHT] |
+    position.bitboards[BLACK_PAWN];
+  bitboard_t friendly_pawns = position.bitboards[BLACK_PAWN];
+  bitboard_t y = friendly_pieces | enemy_bitboard;
+  bitboard_t x = ~((friendly_pawns >> 8) & y) & (friendly_pawns >> 8);
+  bitboard_t first_move_x = x & BITMASK_RANK_6;
+
+  first_move_x |= (first_move_x >> 8) & (~y);
+  x |= first_move_x;
+
+  return x;
+}
+
+void get_pawn_moves(moves_t* moves, position_t position) {
+  assert_valid_position(position);
+
+  bitboard_t forward_moves;
+  bitboard_t friendly_pawns;
+  bitboard_t enemy_bitboard;
+  if (position.turn == WHITE_TURN) {
+    forward_moves = get_white_pawn_forwardmoves(moves, position);
+    friendly_pawns = position.bitboards[WHITE_PAWN];
+    enemy_bitboard = blacks(position);
+  } else {
+    forward_moves = get_black_pawn_forwardmoves(moves, position);
+    friendly_pawns = position.bitboards[BLACK_PAWN];
+    enemy_bitboard = whites(position);
+  }
+
+  bitboard_t file_masks[8] = {
+    BITMASK_FILE_A,
+    BITMASK_FILE_B,
+    BITMASK_FILE_C,
+    BITMASK_FILE_D,
+    BITMASK_FILE_E,
+    BITMASK_FILE_F,
+    BITMASK_FILE_G,
+    BITMASK_FILE_H,
+  };
+
+  for (int i = 0; i < 8; i++) {
+    bitboard_t item = file_masks[i] & forward_moves;
+    bitboard_t pawns = file_masks[i] & friendly_pawns;
+
+    int from = __builtin_ctzll(pawns);
+    pawns &= (pawns - 1);
+    int next_from = __builtin_ctzll(pawns);
+    if (pawns == 0) next_from = 64; // to work around UB
+    
+    while (item) {
+      int to = __builtin_ctzll(item);
+      if (to > next_from) {
+        from = next_from;
+        pawns &= (pawns - 1);
+        next_from = __builtin_ctzll(pawns);
+        if (pawns == 0) next_from = 64;
+      }
+      item &= (item - 1);
+      add_move(moves, from, to);
+    }
+  }
+
+  if (position.passantable_file != 0) {
+    bitboard_t PASSANT_RANK;
+    int rank_shift;
+    int from_shift;
+    if (position.turn == WHITE_TURN) {
+      PASSANT_RANK = BITMASK_RANK_5;
+      rank_shift = 40;
+      from_shift = -9;
+    } else {
+      PASSANT_RANK = BITMASK_RANK_4;
+      from_shift = 7;
+      rank_shift = 16;
+    }
+
+    int left = 0, right = 0;
+    if (position.passantable_file > 1) left = position.passantable_file - 1;
+    if (position.passantable_file < 8) right = position.passantable_file + 1;
+    if (left != 0) {
+      bitboard_t MASK = file_masks[left - 1] & friendly_pawns & PASSANT_RANK;
+      if (MASK != 0) {
+        add_move(
+          moves,
+          left + rank_shift + from_shift,
+          position.passantable_file + rank_shift - 1
+        );
+      }
+    }
+    if (right != 0) {
+      bitboard_t MASK = file_masks[right - 1] & friendly_pawns & PASSANT_RANK;
+      if (MASK != 0) {
+        add_move(
+          moves,
+          right + rank_shift + from_shift,
+          position.passantable_file + rank_shift - 1
+        );
+      }
+    }
+  }
+
+
+  bitboard_t ATTACK_MASK;
+  int shift;
+  if (position.turn == WHITE_TURN) {
+    shift = 0;
+  } else {
+    shift = -16;
+  }
+  for (int i = 0; i < 8; i++) {
+    if (i == 0) ATTACK_MASK = 512;
+    else if (i == 7) ATTACK_MASK = 128;
+    else {
+      ATTACK_MASK = 640;
+    }
+    bitboard_t pawns = file_masks[i] & friendly_pawns;
+    while (pawns) {
+      int from = __builtin_ctzll(pawns);
+      pawns &= pawns - 1;
+
+      bitboard_t MASK; 
+      if (from + shift > 0) {
+        MASK = ATTACK_MASK << (from + shift);
+      } else {
+        MASK = ATTACK_MASK >> -(from + shift);
+      }
+
+      MASK &= enemy_bitboard;
+      while (MASK) {
+        int to = __builtin_ctzll(MASK);
+        MASK &= MASK - 1;
+        add_move(moves, from, to);
+      }
+    }
+  }
+}
-- 
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