From e0a9cb25b0af87723d50cb8d8cffa10f1ebf7dcc Mon Sep 17 00:00:00 2001
From: "Wladimir J. van der Laan" <laanwj@gmail.com>
Date: Tue, 22 Nov 2016 09:59:50 +0100
Subject: [PATCH] bench: Fix subtle counting issue when rescaling iteration
 count

Make sure that the count is a zero modulo the new mask before
scaling, otherwise the next time until a measure triggers
will take only 1/2 as long as accounted for. This caused
the 'min time' to be potentially off by as much as 100%.
---
 src/bench/bench.cpp | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/bench/bench.cpp b/src/bench/bench.cpp
index 227546a7a7..8942da8c74 100644
--- a/src/bench/bench.cpp
+++ b/src/bench/bench.cpp
@@ -64,8 +64,11 @@ bool State::KeepRunning()
           return true;
         }
         if (elapsed*16 < maxElapsed) {
-          countMask = ((countMask<<1)|1) & ((1LL<<60)-1);
-          countMaskInv = 1./(countMask+1);
+          uint64_t newCountMask = ((countMask<<1)|1) & ((1LL<<60)-1);
+          if ((count & newCountMask)==0) {
+              countMask = newCountMask;
+              countMaskInv = 1./(countMask+1);
+          }
         }
     }
     lastTime = now;