Fix ambiguity between clamp implementations

There is an ambiguity between global and std clamp implementations when compiling in c++17,
and on certain toolchains that are not strictly conforming to c++11.
This is solved by putting our clamp implementation in a namespace.

closes https://github.com/official-stockfish/Stockfish/pull/2572

No functional change.

AUTHORS

@@ -48,6 +48,7 @@ fanon
 Fauzi Akram Dabat (FauziAkram)
 Felix Wittmann
 gamander
+Gary Heckman (gheckman)
 gguliash
 Gian-Carlo Pascutto (gcp)
 Gontran Lemaire (gonlem)

src/bitboard.h

@@ -255,9 +255,6 @@ template<> inline int distance<File>(Square x, Square y) { return std::abs(file_
 template<> inline int distance<Rank>(Square x, Square y) { return std::abs(rank_of(x) - rank_of(y)); }
 template<> inline int distance<Square>(Square x, Square y) { return SquareDistance[x][y]; }
 
-template<class T> constexpr const T& clamp(const T& v, const T& lo, const T&  hi) {
-  return v < lo ? lo : v > hi ? hi : v;
-}
 
 /// attacks_bb() returns a bitboard representing all the squares attacked by a
 /// piece of type Pt (bishop or rook) placed on 's'.

src/evaluate.cpp

@@ -236,8 +236,8 @@ namespace {
     attackedBy2[Us] = dblAttackByPawn | (attackedBy[Us][KING] & attackedBy[Us][PAWN]);
 
     // Init our king safety tables
-    Square s = make_square(clamp(file_of(ksq), FILE_B, FILE_G),
+    Square s = make_square(Utility::clamp(file_of(ksq), FILE_B, FILE_G),
-                           clamp(rank_of(ksq), RANK_2, RANK_7));
+                           Utility::clamp(rank_of(ksq), RANK_2, RANK_7));
     kingRing[Us] = PseudoAttacks[KING][s] | s;
 
     kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));

src/material.cpp

@@ -129,7 +129,7 @@ Entry* probe(const Position& pos) {
 
   Value npm_w = pos.non_pawn_material(WHITE);
   Value npm_b = pos.non_pawn_material(BLACK);
-  Value npm   = clamp(npm_w + npm_b, EndgameLimit, MidgameLimit);
+  Value npm   = Utility::clamp(npm_w + npm_b, EndgameLimit, MidgameLimit);
 
   // Map total non-pawn material into [PHASE_ENDGAME, PHASE_MIDGAME]
   e->gamePhase = Phase(((npm - EndgameLimit) * PHASE_MIDGAME) / (MidgameLimit - EndgameLimit));

src/misc.h

@@ -64,6 +64,14 @@ std::ostream& operator<<(std::ostream&, SyncCout);
 #define sync_cout std::cout << IO_LOCK
 #define sync_endl std::endl << IO_UNLOCK
 
+namespace Utility {
+
+/// Clamp a value between lo and hi. Available in c++17.
+template<class T> constexpr const T& clamp(const T& v, const T& lo, const T& hi) {
+  return v < lo ? lo : v > hi ? hi : v;
+}
+
+}
 
 /// xorshift64star Pseudo-Random Number Generator
 /// This class is based on original code written and dedicated

src/pawns.cpp

@@ -193,7 +193,7 @@ Score Entry::evaluate_shelter(const Position& pos, Square ksq) {
 
   Score bonus = make_score(5, 5);
 
-  File center = clamp(file_of(ksq), FILE_B, FILE_G);
+  File center = Utility::clamp(file_of(ksq), FILE_B, FILE_G);
   for (File f = File(center - 1); f <= File(center + 1); ++f)
   {
       b = ourPawns & file_bb(f);

src/search.cpp

@@ -365,7 +365,7 @@ void Thread::search() {
   // for match (TC 60+0.6) results spanning a wide range of k values.
   PRNG rng(now());
   double floatLevel = Options["UCI_LimitStrength"] ?
-                        clamp(std::pow((Options["UCI_Elo"] - 1346.6) / 143.4, 1 / 0.806), 0.0, 20.0) :
+                      Utility::clamp(std::pow((Options["UCI_Elo"] - 1346.6) / 143.4, 1 / 0.806), 0.0, 20.0) :
                         double(Options["Skill Level"]);
   int intLevel = int(floatLevel) +
                  ((floatLevel - int(floatLevel)) * 1024 > rng.rand<unsigned>() % 1024  ? 1 : 0);
@@ -538,7 +538,7 @@ void Thread::search() {
       {
           double fallingEval = (332 +  6 * (mainThread->previousScore - bestValue)
                                     +  6 * (mainThread->iterValue[iterIdx]  - bestValue)) / 704.0;
-          fallingEval = clamp(fallingEval, 0.5, 1.5);
+          fallingEval = Utility::clamp(fallingEval, 0.5, 1.5);
 
           // If the bestMove is stable over several iterations, reduce time accordingly
           timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.94 : 0.91;
@@ -1197,7 +1197,7 @@ moves_loop: // When in check, search starts from here
           else if (depth < 8 && moveCount > 2)
               r++;
 
-          Depth d = clamp(newDepth - r, 1, newDepth);
+          Depth d = Utility::clamp(newDepth - r, 1, newDepth);
 
           value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);