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Revert "Allowing singular extension in mate positions"

It was causing an assert: value > -VALUE_INFINITE
under some conditions.

See official-stockfish#2036

Bench: 3318033
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mcostalba committed Mar 9, 2019
1 parent 1aab5b4 commit 4d0981fef37c85edfd7a0e713d68a4542d7a6784
Showing with 3 additions and 2 deletions.
  1. +3 −2 src/search.cpp
@@ -914,12 +914,13 @@ namespace {
&& move == ttMove
&& !rootNode
&& !excludedMove // Avoid recursive singular search
&& ttValue != VALUE_NONE
/* && ttValue != VALUE_NONE Already implicit in the next condition */
&& abs(ttValue) < VALUE_KNOWN_WIN
&& (tte->bound() & BOUND_LOWER)
&& tte->depth() >= depth - 3 * ONE_PLY
&& pos.legal(move))
{
Value singularBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
Value singularBeta = ttValue - 2 * depth / ONE_PLY;
ss->excludedMove = move;
value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, depth / 2, cutNode);
ss->excludedMove = MOVE_NONE;

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