clang-tidy: Add performance-type-promotion-in-math-fn check

https://clang.llvm.org/extra/clang-tidy/checks/performance/type-promotion-in-math-fn.html

Author: hebasto

src/.clang-tidy

@@ -10,6 +10,7 @@ performance-for-range-copy,
 performance-inefficient-vector-operation,
 performance-move-const-arg,
 performance-no-automatic-move,
+performance-type-promotion-in-math-fn
 performance-unnecessary-copy-initialization,
 readability-const-return-type,
 readability-redundant-declaration,

src/qt/trafficgraphwidget.cpp

@@ -68,8 +68,8 @@ void TrafficGraphWidget::paintEvent(QPaintEvent *)
     painter.drawLine(XMARGIN, YMARGIN + h, width() - XMARGIN, YMARGIN + h);
 
     // decide what order of magnitude we are
-    int base = floor(log10(fMax));
-    float val = pow(10.0f, base);
+    int base = std::floor(std::log10(fMax));
+    float val = std::pow(10.0f, base);
 
     const QString units = tr("kB/s");
     const float yMarginText = 2.0;