Those benchmark ratios are not comparable across languages. The C code compares running time with a very standard mergesort. The C++ code compares with std::s

Those benchmark ratios are not comparable across languages. The C code compares running time with a very standard mergesort. The C++ code compares with std::stable_sort. The Java code compares with a standard mergesort -- very similar to the code in the C version -- but has hard-to-predict JIT warmup effects.