Remove rootDelta branch

This makes rootDelta logic easier to understand, recalculating the value
where it belongs so removes an unnecessary branch.

No functional change

.gitignore

@@ -4,6 +4,7 @@
 src/.depend
 
 # Files from Qt
+build
 CMakeLists.txt
 CMakeLists.txt.user
 

src/search.cpp

@@ -285,6 +285,7 @@ void Search::Worker::iterative_deepening() {
                 // for every four searchAgain steps (see issue #2717).
                 Depth adjustedDepth =
                   std::max(1, rootDepth - failedHighCnt - 3 * (searchAgainCounter + 1) / 4);
+                rootDelta = beta - alpha;
                 bestValue = search<Root>(rootPos, ss, alpha, beta, adjustedDepth, false);
 
                 // Bring the best move to the front. It is critical that sorting
@@ -538,8 +539,6 @@ Value Search::Worker::search(
         if (alpha >= beta)
             return alpha;
     }
-    else
-        thisThread->rootDelta = beta - alpha;
 
     assert(0 <= ss->ply && ss->ply < MAX_PLY);
 
@@ -670,8 +669,7 @@ Value Search::Worker::search(
         && eval - futility_margin(depth, cutNode && !ss->ttHit, improving, opponentWorsening)
                - (ss - 1)->statScore / 210
              >= beta
-        && eval >= beta && eval < 18675  // smaller than wins.
-        && (!ttMove || ttCapture))
+        && eval >= beta && eval < VALUE_MATE_IN_MAX_PLY && (!ttMove || ttCapture))
         return beta > VALUE_MATED_IN_MAX_PLY ? (eval + beta) / 2 : eval;
 
     // Step 8. Null move search with verification search (~35 Elo)