Bug fix for superslab meta-data (#302)

* Replace time measuring macro

The DO_TIME macro was used originally to get performance numbers. The
macro makes tests hard to debug. This commit replaces it with a proper
C++ class with destructor.

* Bug fix

If the superslab meta data is large, then the calculation for the
sizeclasses that could use the short slab was incorrect.  This fixes
that calculation.

Co-authored-by: Nathaniel Wesley Filardo <nfilardo@microsoft.com>

src/test/measuretime.h

@@ -3,12 +3,19 @@
 #include <chrono>
 #include <iomanip>
 #include <iostream>
+#include <sstream>
 
-#define DO_TIME(name, code) \
-  { \
-    auto start__ = std::chrono::high_resolution_clock::now(); \
-    code auto finish__ = std::chrono::high_resolution_clock::now(); \
-    auto diff__ = finish__ - start__; \
-    std::cout << name << ": " << std::setw(12) << diff__.count() << " ns" \
-              << std::endl; \
+class MeasureTime : public std::stringstream
+{
+  std::chrono::time_point<std::chrono::high_resolution_clock> start =
+    std::chrono::high_resolution_clock::now();
+
+public:
+  ~MeasureTime()
+  {
+    auto finish = std::chrono::high_resolution_clock::now();
+    auto diff = finish - start;
+    std::cout << str() << ": " << std::setw(12) << diff.count() << " ns"
+              << std::endl;
   }
+};