Move CMedianFilter to timedata.cpp

Now that we no longer use the median filter to keep track of
the number of blocks of peers, that's the only place it is used.

src/timedata.h

@@ -6,9 +6,68 @@
 #define BITCOIN_TIMEDATA_H
 
 #include <stdint.h>
+#include <vector>
+#include <algorithm>
+#include <assert.h>
 
 class CNetAddr;
 
+/** Median filter over a stream of values.
+ * Returns the median of the last N numbers
+ */
+template <typename T> class CMedianFilter
+{
+private:
+    std::vector<T> vValues;
+    std::vector<T> vSorted;
+    unsigned int nSize;
+public:
+    CMedianFilter(unsigned int size, T initial_value):
+        nSize(size)
+    {
+        vValues.reserve(size);
+        vValues.push_back(initial_value);
+        vSorted = vValues;
+    }
+
+    void input(T value)
+    {
+        if(vValues.size() == nSize)
+        {
+            vValues.erase(vValues.begin());
+        }
+        vValues.push_back(value);
+
+        vSorted.resize(vValues.size());
+        std::copy(vValues.begin(), vValues.end(), vSorted.begin());
+        std::sort(vSorted.begin(), vSorted.end());
+    }
+
+    T median() const
+    {
+        int size = vSorted.size();
+        assert(size>0);
+        if(size & 1) // Odd number of elements
+        {
+            return vSorted[size/2];
+        }
+        else // Even number of elements
+        {
+            return (vSorted[size/2-1] + vSorted[size/2]) / 2;
+        }
+    }
+
+    int size() const
+    {
+        return vValues.size();
+    }
+
+    std::vector<T> sorted () const
+    {
+        return vSorted;
+    }
+};
+
 /* Functions to keep track of adjusted P2P time */
 int64_t GetTimeOffset();
 int64_t GetAdjustedTime();