From e9e7a7b83f78b5c7d29f69083589b449d9b52390 Mon Sep 17 00:00:00 2001
From: Sebastian Buchwald <UniQP@web.de>
Date: Sat, 7 Jan 2023 14:53:59 +0100
Subject: [PATCH] Replace some std::string occurrences with std::string_view

std::string_view is more lightweight than std::string. Furthermore,
std::string_view variables can be declared constexpr.

closes https://github.com/official-stockfish/Stockfish/pull/4328

No functional change
---
 src/misc.cpp               | 9 +++++----
 src/nnue/evaluate_nnue.cpp | 7 ++++---
 src/position.cpp           | 3 ++-
 src/syzygy/tbprobe.cpp     | 5 +++--
 4 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/src/misc.cpp b/src/misc.cpp
index be7abba5..b651972b 100644
--- a/src/misc.cpp
+++ b/src/misc.cpp
@@ -41,12 +41,13 @@ typedef WORD(*fun5_t)();
 }
 #endif
 
+#include <cstdlib>
 #include <fstream>
 #include <iomanip>
 #include <iostream>
 #include <sstream>
+#include <string_view>
 #include <vector>
-#include <cstdlib>
 
 #if defined(__linux__) && !defined(__ANDROID__)
 #include <stdlib.h>
@@ -68,7 +69,7 @@ namespace Stockfish {
 namespace {
 
 /// Version number or dev.
-const string version = "dev";
+constexpr string_view version = "dev";
 
 /// Our fancy logging facility. The trick here is to replace cin.rdbuf() and
 /// cout.rdbuf() with two Tie objects that tie cin and cout to a file stream. We
@@ -151,13 +152,13 @@ string engine_info(bool to_uci) {
   stringstream ss;
   ss << "Stockfish " << version << setfill('0');
 
-  if (version == "dev")
+  if constexpr (version == "dev")
   {
       ss << "-";
       #ifdef GIT_DATE
       ss << GIT_DATE;
       #else
-      const string months("Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec");
+      constexpr string_view months("Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec");
       string month, day, year;
       stringstream date(__DATE__); // From compiler, format is "Sep 21 2008"
 
diff --git a/src/nnue/evaluate_nnue.cpp b/src/nnue/evaluate_nnue.cpp
index 06281da0..f132de71 100644
--- a/src/nnue/evaluate_nnue.cpp
+++ b/src/nnue/evaluate_nnue.cpp
@@ -18,11 +18,12 @@
 
 // Code for calculating NNUE evaluation function
 
+#include <fstream>
+#include <iomanip>
 #include <iostream>
 #include <set>
 #include <sstream>
-#include <iomanip>
-#include <fstream>
+#include <string_view>
 
 #include "../evaluate.h"
 #include "../position.h"
@@ -210,7 +211,7 @@ namespace Stockfish::Eval::NNUE {
     return t;
   }
 
-  static const std::string PieceToChar(" PNBRQK  pnbrqk");
+  constexpr std::string_view PieceToChar(" PNBRQK  pnbrqk");
 
 
   // format_cp_compact() converts a Value into (centi)pawns and writes it in a buffer.
diff --git a/src/position.cpp b/src/position.cpp
index e82425af..cfd98f68 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -22,6 +22,7 @@
 #include <cstring> // For std::memset, std::memcmp
 #include <iomanip>
 #include <sstream>
+#include <string_view>
 
 #include "bitboard.h"
 #include "misc.h"
@@ -46,7 +47,7 @@ namespace Zobrist {
 
 namespace {
 
-const string PieceToChar(" PNBRQK  pnbrqk");
+constexpr std::string_view PieceToChar(" PNBRQK  pnbrqk");
 
 constexpr Piece Pieces[] = { W_PAWN, W_KNIGHT, W_BISHOP, W_ROOK, W_QUEEN, W_KING,
                              B_PAWN, B_KNIGHT, B_BISHOP, B_ROOK, B_QUEEN, B_KING };
diff --git a/src/syzygy/tbprobe.cpp b/src/syzygy/tbprobe.cpp
index cc5e2852..bbfd819d 100644
--- a/src/syzygy/tbprobe.cpp
+++ b/src/syzygy/tbprobe.cpp
@@ -24,9 +24,10 @@
 #include <fstream>
 #include <iostream>
 #include <list>
+#include <mutex>
 #include <sstream>
+#include <string_view>
 #include <type_traits>
-#include <mutex>
 
 #include "../bitboard.h"
 #include "../movegen.h"
@@ -70,7 +71,7 @@ enum TBFlag { STM = 1, Mapped = 2, WinPlies = 4, LossPlies = 8, Wide = 16, Singl
 inline WDLScore operator-(WDLScore d) { return WDLScore(-int(d)); }
 inline Square operator^(Square s, int i) { return Square(int(s) ^ i); }
 
-const std::string PieceToChar = " PNBRQK  pnbrqk";
+constexpr std::string_view PieceToChar = " PNBRQK  pnbrqk";
 
 int MapPawns[SQUARE_NB];
 int MapB1H1H7[SQUARE_NB];
-- 
2.39.2