From f8de41798776f8c00b277391fb984dcfd256de5d Mon Sep 17 00:00:00 2001
From: Bruce Allen <bruce.allen@aei.mpg.de>
Date: Fri, 29 Apr 2005 19:22:43 +0000
Subject: [PATCH] Fixed update_average() function to do the right thing when
 the time between successive calls is small (zero seconds):

Consider the limit
as diff->0, using the first-order Taylor expansion of
exp(x)=1+x+O(x^2).
So to the lowest order in diff:
weight = 1 - diff ln(2) / half_life
so one has
avg += (1-weight)*(work/diff_days)
avg += [diff*ln(2)/half_life] * (work*SECONDS_PER_DAY/diff)
notice that diff cancels out, leaving
avg += [ln(2)/half_life] * work*SECONDS_PER_DAY

svn path=/trunk/boinc/; revision=5978
---
 checkin_notes       |  3 +++
 html/inc/credit.inc | 10 ++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/checkin_notes b/checkin_notes
index b441105479..5a8a198863 100755
--- a/checkin_notes
+++ b/checkin_notes
@@ -5870,4 +5870,7 @@ Bruce 29 April 2005
 	
     lib/
         util.C
+    html/
+        inc/
+            credit.inc
 
diff --git a/html/inc/credit.inc b/html/inc/credit.inc
index 7cdcb56350..e4ab635191 100644
--- a/html/inc/credit.inc
+++ b/html/inc/credit.inc
@@ -8,11 +8,17 @@ define("CREDIT_HALF_LIFE", 86400*7);
 function update_average($now, $work_start_time, $work, &$avg, &$avg_time) {
     if ($avg_time) {
         $diff = $now - $avg_time;
-        if ($diff <=0) $diff = 3600;
+        if ($diff <0) $diff = 0;
         $diff_days = $diff/86400;
         $weight = exp(-$diff*M_LN2/CREDIT_HALF_LIFE);
         $avg *= $weight;
-        $avg += (1-$weight)*($work/$diff_days);
+
+        if ((1.0-$weight)>0.000001) {
+            $avg += (1.0-$weight)*($work/$diff_days);
+        }
+        else {
+            $avg += M_LN2*work*86400/CREDIT_HALF_LIFE;
+        }
     } else if ($work) {
         $dd = ($now - $work_start_time)/86400;
         $avg = $work/$dd;