Fix an assert in Probcut

mcostalba · mcostalba · commit 012f20d66ec0 · 2014-02-22T10:38:21.000+01:00
When running the following position:

8/kPp5/2P3p1/p1P1p1P1/2PpPp2/3p1p2/3P1P2/5K2 w - - 0 1

An assert is raised at depth 92:

assert(-VALUE_INFINITE &lt;= alpha &amp;&amp; alpha &lt; beta &amp;&amp; beta &lt;= VALUE_INFINITE);

This is because it happens that beta = 29832,
so rbeta = 30032 that is &gt; VALUE_INFINITE

Bug spotted and analyzed by Uri, fix suggested by Joerg.

Other fixes where possible but this one is pointed
exactly at the source of the bug, so it is the best
from a code documentation point of view.

bench: 8430785
diff --git a/src/search.cpp b/src/search.cpp
@@ -668,7 +668,7 @@ namespace {
         && !ss->skipNullMove
         &&  abs(beta) < VALUE_MATE_IN_MAX_PLY)
     {
-        Value rbeta = beta + 200;
+        Value rbeta = std::min(beta + 200, VALUE_INFINITE);
         Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
 
         assert(rdepth >= ONE_PLY);

Original file line number	Diff line number	Diff line change
`@@ -668,7 +668,7 @@ namespace {`
`668`	`668`	`&& !ss->skipNullMove`
`669`	`669`	`&& abs(beta) < VALUE_MATE_IN_MAX_PLY)`
`670`	`670`	`{`
`671`		`- Value rbeta = beta + 200;`
	`671`	`+ Value rbeta = std::min(beta + 200, VALUE_INFINITE);`
`672`	`672`	`Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;`
`673`	`673`
`674`	`674`	`assert(rdepth >= ONE_PLY);`