refactor xml parser, uses faster string to double conversion

Util/StringUtil.h

@@ -126,6 +126,40 @@ static inline uint64_t stringToInt64(const std::string& input) {
     return value;
 }
 
+// source: http://tinodidriksen.com/2011/05/28/cpp-convert-string-to-double-speed/
+static inline double StringToDouble(const char *p)
+{
+    double r = 0.0;
+    bool neg = false;
+    if (*p == '-')
+    {
+        neg = true;
+        ++p;
+    }
+    while (*p >= '0' && *p <= '9')
+    {
+        r = (r*10.0) + (*p - '0');
+        ++p;
+    }
+    if (*p == '.')
+    {
+        double f = 0.0;
+        int n = 0;
+        ++p;
+        while (*p >= '0' && *p <= '9')
+        {
+            f = (f*10.0) + (*p - '0');
+            ++p;
+            ++n;
+        }
+        r += f / std::pow(10.0, n);
+    }
+    if (neg)
+    {
+        r = -r;
+    }
+    return r;
+}
 
 static inline void doubleToString(const double value, std::string & output){
     output.clear();