Set IID half way between d/2 and d-4

mcostalba · mcostalba · commit 7d42d02ec77a · 2013-03-30T22:26:30.000+01:00
Master IID formula is depth / 2
Previous patch is depth - 4 * ONE_PLY

This one is the middle way:

(dept/2 + depth-4*ONE_PLY)/2  -&gt; depth-2*ONE_PLY-depth/4

After 16000 games at 60+0.05 th 1
ELO: 4.08 +-3.1 (95%) LOS: 99.5%
Total: 16000 W: 2742 L: 2554 D: 10704

bench: 4781239
diff --git a/src/search.cpp b/src/search.cpp
@@ -745,7 +745,7 @@ namespace {
         && ttMove == MOVE_NONE
         && (PvNode || (!inCheck && ss->staticEval + Value(256) >= beta)))
     {
-        Depth d = (PvNode ? depth - 2 * ONE_PLY : depth - 4 * ONE_PLY);
+        Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
 
         ss->skipNullMove = true;
         search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);

Original file line number	Diff line number	Diff line change
`@@ -745,7 +745,7 @@ namespace {`
`745`	`745`	`&& ttMove == MOVE_NONE`
`746`	`746`	`&& (PvNode \|\| (!inCheck && ss->staticEval + Value(256) >= beta)))`
`747`	`747`	`{`
`748`		`- Depth d = (PvNode ? depth - 2 * ONE_PLY : depth - 4 * ONE_PLY);`
	`748`	`+ Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);`
`749`	`749`
`750`	`750`	`ss->skipNullMove = true;`
`751`	`751`	`search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);`