From 9395e857db95481f6e2494d3a841632be0ff97c8 Mon Sep 17 00:00:00 2001
From: Aargh Rai <aargh.rai+git@gmail.com>
Date: Sat, 18 Jul 2026 14:02:18 +0530
Subject: fixed moved gen & adding messages on asserts

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 Plan.md | 100 ----------------------------------------------------------------
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-# Gacrux: Pseudo-Legal to Legal Move Conversion Plan
-
-## Current State
-- Move generators produce **pseudo-legal** moves (follow piece movement rules but ignore checks/pins)
-- `position_make_move()` has multiple bugs
-- No attack detection or legal move filtering exists
-- Perft test conditions are inverted
-
-## Phase 1: Fix Existing Bugs
-
-### `src/engine/moves.c` — `position_make_move()`
-1. **Lines 94, 100**: Add missing semicolons after `assert(0)`
-2. **Lines 54-55**: Black long castle modifies `WHITE_ROOK` → should be `BLACK_ROOK`
-3. **Lines 71-73**: Black short castle modifies `WHITE_KING`/`WHITE_ROOK` → should be `BLACK_KING`/`BLACK_ROOK`
-4. **Lines 96, 98**: `move.from` (u8) compared against `u64` bitboard constants → use square indices 63 and 56
-5. **Missing turn toggle**: `position->turn` never flips after a move
-
-### `test_perft_starting_position`
-6. **Lines 169-176**: `==` → `!=` (test currently passes when counts are wrong)
-
-## Phase 2: Attack Detection
-
-Create `src/engine/moves/attack.c` with:
-```c
-bool square_attacked(position_t position, square_t square, u8 by_color);
-```
-
-Checks if any piece of `by_color` attacks `square`:
-- **Pawn attacks**: Check diagonally forward for enemy pawns
-- **Knight attacks**: Use existing `knight_moves[64]` lookup
-- **King attacks**: Use existing `920078ULL` pattern
-- **Sliding attacks**: Walk rays from target square (for now, ray-walking)
-
-## Phase 3: Legal Move Filtering
-
-Modify `get_moves()` (or add `get_legal_moves()`) to:
-1. Generate all pseudo-legal moves
-2. For each move, make it on a copy of the position
-3. Find the friendly king in the resulting position
-4. Check if the friendly king is attacked by the opponent
-5. If attacked → remove the move (swap with last, decrement length)
-
-**Castling pre-checks** (in `king.c`):
-- King not currently in check
-- Squares king passes through are not attacked
-- No pieces between king and rook
-
-## Phase 4: Magic Bitboards (Performance Optimization)
-
-Replace ray-walking with O(1) magic lookups for sliding piece attacks.
-
-### Data Structure
-```c
-typedef struct {
-    bitboard_t mask;     // relevant occupancy bits (excludes edges)
-    bitboard_t *attacks; // pointer into attack table
-    bitboard_t magic;    // the magic multiplier
-    int shift;           // 64 - popcount(mask)
-} magic_t;
-```
-
-### Attack Tables
-- `rook_attacks[0x19000]` (~100KB)
-- `bishop_attacks[0x1480]` (~5KB)
-
-### Index Computation
-```c
-unsigned index = ((occupied & magic.mask) * magic.magic) >> magic.shift;
-return magic.attacks[index];
-```
-
-### Initialization
-At startup, for each square:
-1. Compute mask (pseudo-attacks minus edges)
-2. Enumerate all subsets of the mask
-3. Compute true attacks via ray-walking (reference)
-4. Find magic number via PRNG search
-
-### Usage
-```c
-// Move generation
-bitboard_t attacks = get_rook_attacks(from_square, all_occupied);
-attacks &= ~friendly_pieces;
-
-// Attack detection
-bool square_attacked(...) {
-    if (get_rook_attacks(sq, occ) & (enemy_rooks | enemy_queens)) return true;
-    if (get_bishop_attacks(sq, occ) & (enemy_bishops | enemy_queens)) return true;
-    // ...
-}
-```
-
-## Implementation Order
-1. Fix bugs (Phase 1)
-2. Add `square_attacked()` with ray-walking
-3. Add legal move filtering
-4. Fix castling legality
-5. Verify perft d0-d7
-6. Uncomment + verify Kiwipete perft
-7. Add magic bitboards (Phase 4)
-- 
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