Revert scale factor in pawn evaluation

It simply doesn't seems to work both in direct matches
and in balance tuning.

So revert the idea.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/evaluate.cpp

@@ -430,13 +430,6 @@ Value do_evaluate(const Position& pos, EvalInfo& ei, int threadID) {
           factor[BLACK] = sf;
   }
 
-  // If we don't already have an unusual scale factor, use pawn
-  // evaluation ones.
-  if (factor[WHITE] == SCALE_FACTOR_NORMAL)
-      factor[WHITE] = ei.pi->scale_factor(WHITE);
-  if (factor[BLACK] == SCALE_FACTOR_NORMAL)
-      factor[BLACK] = ei.pi->scale_factor(BLACK);
-
   // Interpolate between the middle game and the endgame score
   Color stm = pos.side_to_move();
 

src/material.cpp

@@ -304,7 +304,7 @@ MaterialInfo* MaterialInfoTable::get_material_info(const Position& pos) {
     {
         if (   pos.non_pawn_material(c) == pos.non_pawn_material(opposite_color(c))
             || pos.non_pawn_material(c) < RookValueMidgame)
-            mi->factor[c] = SCALE_FACTOR_ZERO;
+            mi->factor[c] = 0;
         else
         {
             switch (pos.piece_count(c, BISHOP)) {

src/pawns.cpp

@@ -70,13 +70,6 @@ namespace {
     S(34,68), S(83,166), S(0, 0), S( 0, 0)
   };
 
-  // UnpairedPawnsTable[] gives a score according to the number
-  // of panws that do not have an enemy pawn in front of them.
-  const int UnpairedPawnsTable[16] = { 32, 48, 64, 80, 96, 112, 128, 128, 128 };
-
-  // PawnsQtyTable[] gives a score according to the number of panws
-  const int PawnsQtyTable[16] = { 16, 16, 16, 16, 16, 16, 16, 16, 16 };
-
   // Pawn storm tables for positions with opposite castling
   const int QStormTable[64] = {
     0,  0,  0,  0, 0, 0, 0, 0,
@@ -194,7 +187,6 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
   int bonus;
   Score value = make_score(0, 0);
   const Square* ptr = pos.piece_list_begin(Us, PAWN);
-  int unpairedPawnsNum = pos.piece_count(Us, PAWN);
 
   // Initialize pawn storm scores by giving bonuses for open files
   for (f = FILE_A; f <= FILE_H; f++)
@@ -219,10 +211,6 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
       doubled  = ourPawns & squares_behind(Us, s);
       opposed  = theirPawns & squares_in_front_of(Us, s);
 
-      // Decrease number of unpaired pawns
-      if (opposed)
-          unpairedPawnsNum--;
-
       // We calculate kingside and queenside pawn storm
       // scores for both colors. These are used when evaluating
       // middle game positions with opposite side castling.
@@ -349,9 +337,6 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
           value += CandidateBonus[relative_rank(Us, s)];
   }
 
-  // Calculate a scale factor to be used to evaluate if position is drawish
-  pi->factor[Us] = UnpairedPawnsTable[unpairedPawnsNum] * PawnsQtyTable[pos.piece_count(Us, PAWN)] / 16;
-
   return value;
 }
 

src/pawns.h

@@ -26,7 +26,6 @@
 ////
 
 #include "bitboard.h"
-#include "scale.h"
 #include "value.h"
 
 ////
@@ -53,7 +52,6 @@ public:
   Value queenside_storm_value(Color c) const;
   Bitboard pawn_attacks(Color c) const;
   Bitboard passed_pawns() const;
-  ScaleFactor scale_factor(Color c) const;
   int file_is_half_open(Color c, File f) const;
   int has_open_file_to_left(Color c, File f) const;
   int has_open_file_to_right(Color c, File f) const;
@@ -69,7 +67,8 @@ private:
   Square kingSquares[2];
   Score value;
   int16_t ksStormValue[2], qsStormValue[2];
-  uint8_t halfOpenFiles[2], kingShelters[2], factor[2];
+  uint8_t halfOpenFiles[2];
+  uint8_t kingShelters[2];
 };
 
 /// The PawnInfoTable class represents a pawn hash table.  It is basically
@@ -117,10 +116,6 @@ inline Value PawnInfo::queenside_storm_value(Color c) const {
   return Value(qsStormValue[c]);
 }
 
-inline ScaleFactor PawnInfo::scale_factor(Color c) const {
-  return ScaleFactor(factor[c]);
-}
-
 inline int PawnInfo::file_is_half_open(Color c, File f) const {
   return (halfOpenFiles[c] & (1 << int(f)));
 }

src/scale.h

@@ -33,10 +33,10 @@
 ////
 
 enum ScaleFactor {
-  SCALE_FACTOR_ZERO   = 0,
+  SCALE_FACTOR_ZERO = 0,
   SCALE_FACTOR_NORMAL = 64,
-  SCALE_FACTOR_MAX    = 128,
-  SCALE_FACTOR_NONE   = 255
+  SCALE_FACTOR_MAX = 128,
+  SCALE_FACTOR_NONE = 255
 };