refactor(book): refactoring opening book code

1 files changed, 6 insertions, 12 deletions

diff --git a/src/book.cpp b/src/book.cpp
index e1cd127..abf9693 100644
--- a/src/book.cpp
+++ b/src/book.cpp
@@ -6,13 +6,12 @@
 #include <cstdlib>
 #include <fstream>
 #include <iostream>
+#include <optional>
 #include <random>
 #include <vector>
 
 #include "board/board.hpp"
 
-constexpr int BOOK_DEPTH = 16;
-
 struct BookEntry {
   uint64_t key;
   uint16_t move;
@@ -27,7 +26,7 @@ static std::mt19937 rng{std::random_device{}()};
 void InitBook(const std::string &path) {
   std::ifstream file(path, std::ios::binary);
   if (!file.is_open()) {
-    std::cerr << "info string Could not open book file: " << path << "\n";
+    std::cerr << "info string Failed to open: " << path << "\n";
     return;
   }
 
@@ -74,12 +73,9 @@ void InitBook(const std::string &path) {
                   ((l & 0x00FF0000U) >> 8) | ((l & 0xFF000000U) >> 24);
   }
 
-  std::cerr << "info string Book loaded: " << book.size() << " entries\n";
+  std::cerr << "info string " << path << ": " << book.size() << " entries\n";
 }
 
-// Convert Polyglot move to Mono internal move format.
-// Polyglot: bits 0-5=to, 6-11=from, 12-14=promo (0=N,1=B,2=R,3=Q)
-// Mono:     bits 0-1=promo (00=N,11=B,01=R,10=Q), 2-7=from, 8-13=to
 static uint16_t PolyglotToMono(uint16_t polyglotMove) {
   uint8_t to = polyglotMove & 63;
   uint8_t from = (polyglotMove >> 6) & 63;
@@ -106,9 +102,9 @@ static uint16_t PolyglotToMono(uint16_t polyglotMove) {
   return CreateMove(from, to, promotion);
 }
 
-uint16_t ProbeBook(uint64_t key) {
+std::optional<uint16_t> ProbeBook(uint64_t key) {
   if (book.empty()) {
-    return 0;
+    return {};
   }
 
   // Binary search for first matching entry
@@ -124,7 +120,7 @@ uint16_t ProbeBook(uint64_t key) {
   }
 
   if (matches.empty()) {
-    return 0;
+    return {};
   }
 
   // Weighted random selection
@@ -145,5 +141,3 @@ uint16_t ProbeBook(uint64_t key) {
 
   return PolyglotToMono(matches.back()->move);
 }
-
-int GetBookDepth() { return BOOK_DEPTH; }