From 194048503020ad35e221c36fd8817f569b728310 Mon Sep 17 00:00:00 2001
From: Joost VandeVondele <Joost.VandeVondele@gmail.com>
Date: Mon, 19 Mar 2018 00:16:23 +0100
Subject: [PATCH] Simplify razoring logic

passed STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 36574 W: 7523 L: 7430 D: 21621
http://tests.stockfishchess.org/tests/view/5aae11450ebc590299abf52f

No functional change.
---
 src/search.cpp | 23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/src/search.cpp b/src/search.cpp
index 176006fc..ada0cd5b 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -67,8 +67,7 @@ namespace {
   constexpr int SkipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 };
 
   // Razor and futility margins
-  constexpr int RazorMargin1 = 590;
-  constexpr int RazorMargin2 = 604;
+  constexpr int RazorMargin[] = {0, 590, 604};
   Value futility_margin(Depth d, bool improving) {
     return Value((175 - 50 * improving) * d / ONE_PLY);
   }
@@ -690,21 +689,13 @@ namespace {
 
     // Step 7. Razoring (skipped when in check)
     if (  !PvNode
-        && depth <= 2 * ONE_PLY)
+        && depth <= 2 * ONE_PLY
+        && eval <= alpha - Value(RazorMargin[depth / ONE_PLY]))
     {
-        if (   depth == ONE_PLY
-            && eval + RazorMargin1 <= alpha)
-            return qsearch<NonPV>(pos, ss, alpha, alpha+1);
-
-        else if (eval + RazorMargin2 <= alpha)
-        {
-            Value ralpha = alpha - RazorMargin2;
-
-            Value v = qsearch<NonPV>(pos, ss, ralpha, ralpha+1);
-
-            if (v <= ralpha)
-                return v;
-        }
+        Value ralpha = alpha - Value((depth != ONE_PLY) * RazorMargin[depth / ONE_PLY]);
+        Value v = qsearch<NonPV>(pos, ss, ralpha, ralpha+1);
+        if (depth == ONE_PLY || v <= ralpha)
+            return v;
     }
 
     // Step 8. Futility pruning: child node (skipped when in check)
-- 
2.39.2