Do not hardcode Debug Log File

Allow to specifiy the log file name, this comes
handy in case of self-matches so that each SF
instance writes into a different log file.

No functional change.

src/misc.cpp

@@ -65,23 +65,23 @@ struct Tie: public streambuf { // MSVC requires split streambuf for cin and cout
 class Logger {
 
   Logger() : in(cin.rdbuf(), file.rdbuf()), out(cout.rdbuf(), file.rdbuf()) {}
- ~Logger() { start(false); }
+ ~Logger() { start(""); }
 
   ofstream file;
   Tie in, out;
 
 public:
-  static void start(bool b) {
+  static void start(const std::string& fname) {
 
     static Logger l;
 
-    if (b && !l.file.is_open())
+    if (!fname.empty() && !l.file.is_open())
     {
-        l.file.open("io_log.txt", ifstream::out);
+        l.file.open(fname, ifstream::out);
         cin.rdbuf(&l.in);
         cout.rdbuf(&l.out);
     }
-    else if (!b && l.file.is_open())
+    else if (fname.empty() && l.file.is_open())
     {
         cout.rdbuf(l.out.buf);
         cin.rdbuf(l.in.buf);
@@ -157,7 +157,7 @@ std::ostream& operator<<(std::ostream& os, SyncCout sc) {
 
 
 /// Trampoline helper to avoid moving Logger to misc.h
-void start_logger(bool b) { Logger::start(b); }
+void start_logger(const std::string& fname) { Logger::start(fname); }
 
 
 /// prefetch() preloads the given address in L1/L2 cache. This is a non-blocking

src/misc.h

@@ -31,7 +31,7 @@
 
 const std::string engine_info(bool to_uci = false);
 void prefetch(void* addr);
-void start_logger(bool b);
+void start_logger(const std::string& fname);
 
 void dbg_hit_on(bool b);
 void dbg_hit_on(bool c, bool b);

src/ucioption.cpp

@@ -57,7 +57,7 @@ void init(OptionsMap& o) {
 
   const int MaxHashMB = Is64Bit ? 1024 * 1024 : 2048;
 
-  o["Write Debug Log"]       << Option(false, on_logger);
+  o["Debug Log File"]        << Option("", on_logger);
   o["Contempt"]              << Option(0, -100, 100);
   o["Threads"]               << Option(1, 1, 128, on_threads);
   o["Hash"]                  << Option(16, 1, MaxHashMB, on_hash_size);