From be641e881fdfdf3354453381f832fe7822e7c731 Mon Sep 17 00:00:00 2001
From: Lucas Braesch <lucas.braesch@gmail.com>
Date: Thu, 3 Apr 2014 21:31:42 +0800
Subject: [PATCH] Remove QueenOn7th and QueenOnPawn

Small simplification.

Passed SPRT(-3,1) both at STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 17051 W: 3132 L: 3005 D: 10914

and LTC:
LLR: 4.55 (-2.94,2.94) [-3.00,1.00]
Total: 24890 W: 3842 L: 3646 D: 17402

The rationale behind this is that I've never managed to add a
Queen on 7th rank bonus in DiscoCheck, because it never showed
to be positive (evne slightly) in testing. The only thing that
worked is Rook on 7th rank.

In terms of SF code, it seemed natural to group it with QueenOnPawn
as well as those are done together. I know you're against groupping
in general, but when it comes to non regression test, you are being
more conservative by groupping. If the group passes SPRT(-3,1) it's
safer to commit, than test every component in SPRT(-3,1) and end up
with the risk of commiting several -1 elo regression instead of just
one -1 elo regression.

In chess terms, perhaps it's just easier to manouver a Queen (which
can more also diagonaly) than a Rook. Therefore you can let the search
do its job without needing eval ad-hoc terms to guide it. For the Rook
which takes more moves to manouver such eval terms can be (marginally)
useful.

bench: 7473314
---
 src/evaluate.cpp | 24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index b4e86f3b..28fd8341 100644
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -162,9 +162,7 @@ namespace {
 
   const Score Tempo            = make_score(24, 11);
   const Score RookOn7th        = make_score(11, 20);
-  const Score QueenOn7th       = make_score( 3,  8);
   const Score RookOnPawn       = make_score(10, 28);
-  const Score QueenOnPawn      = make_score( 4, 20);
   const Score RookOpenFile     = make_score(43, 21);
   const Score RookSemiopenFile = make_score(19, 10);
   const Score BishopPawns      = make_score( 8, 12);
@@ -514,23 +512,21 @@ Value do_evaluate(const Position& pos) {
                 score += MinorBehindPawn;
         }
 
-        if (  (Pt == ROOK || Pt == QUEEN)
-            && relative_rank(Us, s) >= RANK_5)
+        if (Pt == ROOK)
         {
-            // Major piece on 7th rank and enemy king trapped on 8th
+            // Rook on 7th rank and enemy king trapped on 8th
             if (   relative_rank(Us, s) == RANK_7
                 && relative_rank(Us, pos.king_square(Them)) == RANK_8)
-                score += Pt == ROOK ? RookOn7th : QueenOn7th;
+                score += RookOn7th;
 
-            // Major piece attacking enemy pawns on the same rank/file
-            Bitboard pawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
-            if (pawns)
-                score += popcount<Max15>(pawns) * (Pt == ROOK ? RookOnPawn : QueenOnPawn);
-        }
+            // Rook piece attacking enemy pawns on the same rank/file
+            if (relative_rank(Us, s) >= RANK_5)
+            {
+                Bitboard pawns = pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s];
+                if (pawns)
+                    score += popcount<Max15>(pawns) * RookOnPawn;
+            }
 
-        // Special extra evaluation for rooks
-        if (Pt == ROOK)
-        {
             // Give a bonus for a rook on a open or semi-open file
             if (ei.pi->semiopen(Us, file_of(s)))
                 score += ei.pi->semiopen(Them, file_of(s)) ? RookOpenFile : RookSemiopenFile;
-- 
2.39.2