fix issue 235 (#236)

src/complexity.cc

@@ -35,9 +35,9 @@ BigOFunc* FittingCurve(BigO complexity) {
     case oNCubed:
       return [](int n) -> double { return n * n * n; };
     case oLogN:
-      return [](int n) { return log2(n); };
+      return [](int n) { return std::log2(n); };
     case oNLogN:
-      return [](int n) { return n * log2(n); };
+      return [](int n) { return n * std::log2(n); };
     case o1:
     default:
       return [](int) { return 1.0; };

test/complexity_test.cc

@@ -10,6 +10,7 @@
 #include <vector>
 #include <utility>
 #include <algorithm>
+#include <cmath>
 
 namespace {
 
@@ -220,7 +221,7 @@ static void BM_Complexity_O_N_log_N(benchmark::State& state) {
   state.SetComplexityN(state.range_x());
 }
 BENCHMARK(BM_Complexity_O_N_log_N) -> RangeMultiplier(2) -> Range(1<<10, 1<<16) -> Complexity(benchmark::oNLogN);
-BENCHMARK(BM_Complexity_O_N_log_N) -> RangeMultiplier(2) -> Range(1<<10, 1<<16) -> Complexity([](int n) {return n * log2(n); });
+BENCHMARK(BM_Complexity_O_N_log_N) -> RangeMultiplier(2) -> Range(1<<10, 1<<16) -> Complexity([](int n) {return n * std::log2(n); });
 BENCHMARK(BM_Complexity_O_N_log_N) -> RangeMultiplier(2) -> Range(1<<10, 1<<16) -> Complexity();
 
 const char* big_o_n_lg_n_test_name = "BM_Complexity_O_N_log_N_BigO";