Confidence ranges were coming in too high and had occasional divide-by-zero...

Confidence ranges were coming in too high and had occasional divide-by-zero leading to CHECK failures. Changed the math and the unit tests to satisfy stricter confidence requirements and remove divide by zero.

BUG=95453
TEST=None

Review URL: http://codereview.chromium.org/7833046

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@99879 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/autocomplete/network_action_predictor.cc

@@ -52,9 +52,9 @@ NetworkActionPredictor::Action
 
   const double base_score = 1.0;
 
-  // This constant is ln(1/0.8) so we end up decaying to 80% of the base score
+  // This constant is ln(1/0.65) so we end up decaying to 65% of the base score
   // for each week that passes.
-  const double kLnDecayPercent = 0.2231435513142097;
+  const double kLnDecayPercent = 0.43078291609245;
   base::TimeDelta time_passed = base::Time::Now() - url_row.last_visit();
 
   // Clamp to 0.
@@ -63,13 +63,12 @@ NetworkActionPredictor::Action
           base::Time::kMicrosecondsPerWeek);
 
   const double kMaxDecaySpeedDivisor = 5.0;
-  const double kNumUsesPerDecaySpeedDivisorIncrement = 1.0;
+  const double kNumUsesPerDecaySpeedDivisorIncrement = 2.0;
   const double decay_divisor = std::min(kMaxDecaySpeedDivisor,
       (url_row.typed_count() + kNumUsesPerDecaySpeedDivisorIncrement - 1) /
           kNumUsesPerDecaySpeedDivisorIncrement);
 
   const double confidence = base_score / exp(decay_exponent / decay_divisor);
-
   CHECK(confidence >= 0.0 && confidence <= 1.0);
 
   UMA_HISTOGRAM_COUNTS_100("NetworkActionPredictor.Confidence",

chrome/browser/autocomplete/network_action_predictor_unittest.cc

@@ -47,11 +47,11 @@ TEST_F(NetworkActionPredictorTest, RecommendAction) {
     { GURL("http://www.testsite.com/b.html"),
       ASCIIToUTF16("Test - site - just a test"), 0, 1,
       ASCIIToUTF16("just"),
-      NetworkActionPredictor::ACTION_NONE },
+      NetworkActionPredictor::ACTION_PRERENDER },
     { GURL("http://www.testsite.com/c.html"),
       ASCIIToUTF16("Test - site - just a test"), 1, 5,
       ASCIIToUTF16("just"),
-      NetworkActionPredictor::ACTION_PRERENDER },
+      NetworkActionPredictor::ACTION_PRECONNECT },
     { GURL("http://www.testsite.com/d.html"),
       ASCIIToUTF16("Test - site - just a test"), 2, 5,
       ASCIIToUTF16("just"),
@@ -67,13 +67,13 @@ TEST_F(NetworkActionPredictorTest, RecommendAction) {
     { GURL("http://www.testsite.com/g.html"),
       ASCIIToUTF16("Test - site - just a test"), 1, 12,
       ASCIIToUTF16("just a"),
-      NetworkActionPredictor::ACTION_PRECONNECT },
+      NetworkActionPredictor::ACTION_NONE },
     { GURL("http://www.testsite.com/h.html"),
-      ASCIIToUTF16("Test - site - just a test"), 1, 21,
+      ASCIIToUTF16("Test - site - just a test"), 2, 21,
       ASCIIToUTF16("just a test"),
-      NetworkActionPredictor::ACTION_PRECONNECT },
+      NetworkActionPredictor::ACTION_NONE },
     { GURL("http://www.testsite.com/i.html"),
-      ASCIIToUTF16("Test - site - just a test"), 1, 28,
+      ASCIIToUTF16("Test - site - just a test"), 3, 28,
       ASCIIToUTF16("just a test"),
       NetworkActionPredictor::ACTION_NONE }
   };