Return a depth with repeats

When a move is detected to lead to a repeat, we return the corresponding
score with a validity depth just enough to satisfy the current depth
request. This prevents earlier positions contaminated by the score to
last unnecessarily long in the hash table.

diff --git a/dropper.c b/dropper.c
index ced95b2..78b97cc 100644 (file)
--- a/dropper.c
+++ b/dropper.c
@@ -1352,6 +1352,7 @@ if(PATH)printf("%d:%d:%d new iter moveStack[%d..%d]\n",ply,depth,iterDepth,m.fir
                    else if(gain == pawn  || gain >= (400<<21)) score = INF-1;  // quasi-repeat with extra piece in hand
                    else if(gain == -pawn || gain <= (-400<<21)) score = 1-INF; // or with one piece less
                    else goto search;// traded one hand piece for another; could still lead somewhere
+                   f.depth = (score >= beta ? highDepth+1 : iterDepth);        // minimum required depth
                    *pvPtr = 0; // fake that daughter returned empty PV
                } else { // not a repeat: search it
                    int lmr;