From b75d7fa34865bf16b826d9a747b346ac944529ee Mon Sep 17 00:00:00 2001
From: Miroslav Stampar <miroslav.stampar@gmail.com>
Date: Tue, 14 Dec 2010 12:22:17 +0000
Subject: [PATCH] minor cache based optimization

---
 lib/core/common.py | 17 ++++++++++++-----
 lib/core/option.py |  1 +
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/lib/core/common.py b/lib/core/common.py
index ddc413f80..413f0b8c7 100644
--- a/lib/core/common.py
+++ b/lib/core/common.py
@@ -1290,13 +1290,20 @@ def stdev(values):
     if not values or len(values) < 2:
         return None
 
-    summa = 0.0
-    avg = average(values)
+    key = (values[0], values[-1], len(values))
 
-    for value in values:
-        summa += pow(value - avg, 2)
+    if key in kb.cache.stdev:
+        return kb.cache.stdev[key]
+    else:
+        summa = 0.0
+        avg = average(values)
 
-    return sqrt(summa/(len(values) - 1))
+        for value in values:
+            summa += pow(value - avg, 2)
+
+        retVal = sqrt(summa/(len(values) - 1))
+        kb.cache.stdev[key] = retVal
+        return retVal
 
 def average(values):
     """
diff --git a/lib/core/option.py b/lib/core/option.py
index dc7bddd64..1861311f3 100644
--- a/lib/core/option.py
+++ b/lib/core/option.py
@@ -1125,6 +1125,7 @@ def __setKnowledgeBaseAttributes():
     kb.cache           = advancedDict()
     kb.cache.content   = {}
     kb.cache.regex     = {}
+    kb.cache.stdev     = {}
 
     kb.commonOutputs   = None