Analytics: changes to QueryEngine

- When the start and end timestamps of a query are equal, it is enforced
that only one sensor value will be retrieved

common/include/cacheentry.h

@@ -164,26 +164,36 @@ public:
 		uint64_t cacheSize = _cache.size()>1 ? _cache.size()-1 : 1;
 		uint64_t staleThreshold = (_maxHistory / cacheSize) * (uint64_t)_batchSize * 4;
         uint64_t now = getTimestamp();
-        //Converting relative offsets to absolute timestamp for staleness checking
-        uint64_t startTsInt = rel ? now - startTs : startTs;
-        uint64_t endTsInt = rel ? now - endTs : endTs;
-        //Getting the cache indexes to access sensor data
-        int64_t startIdx = rel ? getOffset(startTs) : searchTimestamp(startTs, true);
-        int64_t endIdx = rel ? getOffset(endTs) : searchTimestamp(endTs, false);
-
-        //Managing invalid time offsets
-        if(startIdx < 0 || endIdx < 0)
-            return buffer;
-        //Managing obsolete data
-        if(tsAbs(startTsInt, _cache[startIdx].timestamp) > staleThreshold || tsAbs(endTsInt, _cache[endIdx].timestamp) > staleThreshold)
-            return buffer;
-        if(startIdx <= endIdx)
-            buffer->insert(buffer->end(), _cache.begin() + startIdx, _cache.begin() + endIdx + 1);
+        
+        if(startTs!=endTs) {
+            //Converting relative offsets to absolute timestamp for staleness checking
+            uint64_t startTsInt = rel ? now - startTs : startTs;
+            uint64_t endTsInt = rel ? now - endTs : endTs;
+            //Getting the cache indexes to access sensor data
+            int64_t startIdx = rel ? getOffset(startTs) : searchTimestamp(startTs, true);
+            int64_t endIdx = rel ? getOffset(endTs) : searchTimestamp(endTs, false);
+    
+            //Managing invalid time offsets
+            if(startIdx < 0 || endIdx < 0)
+                return buffer;
+            //Managing obsolete data
+            if(tsAbs(startTsInt, _cache[startIdx].timestamp) > staleThreshold || tsAbs(endTsInt, _cache[endIdx].timestamp) > staleThreshold)
+                return buffer;
+            if(startIdx <= endIdx)
+                buffer->insert(buffer->end(), _cache.begin() + startIdx, _cache.begin() + endIdx + 1);
+            else {
+                buffer->insert(buffer->end(), _cache.begin() + startIdx, _cache.end());
+                buffer->insert(buffer->end(), _cache.begin(), _cache.begin() + endIdx + 1);
+            }
+        }
         else {
-            buffer->insert(buffer->end(), _cache.begin() + startIdx, _cache.end());
-            buffer->insert(buffer->end(), _cache.begin(), _cache.begin() + endIdx + 1);
+            // If start and end timestamps are equal we retrieve only one value
+            uint64_t tsInt = rel ? now - startTs : startTs;
+            int64_t intIdx = rel ? getOffset(startTs) : searchTimestamp(startTs, false);
+            if(intIdx < 0 || tsAbs(tsInt, _cache[intIdx].timestamp) > staleThreshold)
+                return buffer;
+            buffer->push_back(_cache[intIdx]);
         }
-
         return buffer;
 	}