Clean functions returning by const values

The codebase contains multiple functions returning by const-value.
This patch is a small cleanup making those function returns
by value instead, removing the const specifier.

closes https://github.com/official-stockfish/Stockfish/pull/3328

No functional change

AUTHORS

@@ -24,6 +24,7 @@ Ali AlZhrani (Cooffe)
 Andrew Grant (AndyGrant)
 Andrey Neporada (nepal)
 Andy Duplain
+Antoine Champion (antoinechampion)
 Aram Tumanian (atumanian)
 Arjun Temurnikar
 Auguste Pop

src/bitboard.cpp

@@ -55,7 +55,7 @@ inline Bitboard safe_destination(Square s, int step) {
 /// Bitboards::pretty() returns an ASCII representation of a bitboard suitable
 /// to be printed to standard output. Useful for debugging.
 
-const std::string Bitboards::pretty(Bitboard b) {
+std::string Bitboards::pretty(Bitboard b) {
 
   std::string s = "+---+---+---+---+---+---+---+---+\n";
 

src/bitboard.h

@@ -33,7 +33,7 @@ bool probe(Square wksq, Square wpsq, Square bksq, Color us);
 namespace Bitboards {
 
 void init();
-const std::string pretty(Bitboard b);
+std::string pretty(Bitboard b);
 
 }
 

src/misc.cpp

@@ -138,7 +138,7 @@ public:
 /// the program was compiled) or "Stockfish <Version>", depending on whether
 /// Version is empty.
 
-const string engine_info(bool to_uci) {
+string engine_info(bool to_uci) {
 
   const string months("Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec");
   string month, day, year;
@@ -161,7 +161,7 @@ const string engine_info(bool to_uci) {
 
 /// compiler_info() returns a string trying to describe the compiler we use
 
-const std::string compiler_info() {
+std::string compiler_info() {
 
   #define stringify2(x) #x
   #define stringify(x) stringify2(x)

src/misc.h

@@ -28,8 +28,8 @@
 
 #include "types.h"
 
-const std::string engine_info(bool to_uci = false);
-const std::string compiler_info();
+std::string engine_info(bool to_uci = false);
+std::string compiler_info();
 void prefetch(void* addr);
 void start_logger(const std::string& fname);
 void* std_aligned_alloc(size_t alignment, size_t size);

src/position.cpp

@@ -408,7 +408,7 @@ Position& Position::set(const string& code, Color c, StateInfo* si) {
 /// Position::fen() returns a FEN representation of the position. In case of
 /// Chess960 the Shredder-FEN notation is used. This is mainly a debugging function.
 
-const string Position::fen() const {
+string Position::fen() const {
 
   int emptyCnt;
   std::ostringstream ss;

src/position.h

@@ -87,7 +87,7 @@ public:
   // FEN string input/output
   Position& set(const std::string& fenStr, bool isChess960, StateInfo* si, Thread* th);
   Position& set(const std::string& code, Color c, StateInfo* si);
-  const std::string fen() const;
+  std::string fen() const;
 
   // Position representation
   Bitboard pieces(PieceType pt) const;