max. OpenMP threads: 4 (4 processors)
Sort of NELEM (200000000) elements in a vector ---------------------

Sorted elements -----------------------------------------------
GCC std::sort - time :6.5046 seconds
cntree::intro_sort - time :4.17959 seconds
GCC parallel::sort - time :3.13488 seconds 
tbb::parallel_sort - time :0.110298 seconds
cntree::parallel_sort - time :1.67314 seconds

GCC std::stable_sort - time :13.0919 seconds
cntree::stable_sort - time :14.9777 seconds
GCC parallel::stable_sort - time :9.73766 seconds
cntree::parallel_stable_sort - time :5.86093 seconds

Reverse sorted elements ---------------------------------------
GCC std::sort - time :4.48113 seconds
cntree::intro_sort - time :4.44266 seconds
GCC parallel::sort - time :2.62495 seconds 
tbb::parallel_sort - time :1.93454 seconds
cntree::parallel_sort - time :1.98576 seconds

GCC std::stable_sort - time :14.5946 seconds
cntree::stable_sort - time :25.6307 seconds
GCC GCC parallel::stable_sort - time :10.1077 seconds
cntree::parallel_stable_sort - time :9.2956 seconds

Random elements, few repeated ( rand() )-----------------------
GCC std::sort - time :38.2609 seconds
cntree::intro_sort - time :40.3978 seconds
GCC parallel::sort - time :7.44974 seconds 
tbb::parallel_sort - time :7.93203 seconds
cntree::parallel_sort - time :7.96778 seconds

GCC std::stable_sort - time :19.0208 seconds
cntree::stable_sort - time :31.7279 seconds
GCC parallel::stable_sort - time :10.6938 seconds
cntree::parallel_stable_sort - time :10.8504 seconds

Random elements, quite repeated ( rand()  % (NELEM/2) )---------
GCC std::sort - time :25.5909 seconds
cntree::intro_sort - time :27.0548 seconds
GCC parallel::sort - time :8.06961 seconds 
tbb::parallel_sort - time :8.34856 seconds
cntree::parallel_sort - time :8.00553 seconds

GCC std::stable_sort - time :21.2383 seconds
cntree::stable_sort - time :31.7613 seconds
GCC parallel::stable_sort - time :10.6575 seconds
cntree::parallel_stable_sort - time :10.6991 seconds

Random element many repeated (rand() % 10000)--------------------
GCC std::sort - time :17.0386 seconds
cntree::intro_sort - time :17.8827 seconds
GCC parallel::sort - time :5.34894 seconds 
tbb::parallel_sort - time :5.96923 seconds
cntree::parallel_sort - time :5.60153 seconds

GCC std::stable_sort - time :19.0441 seconds
cntree::stable_sort - time :31.7324 seconds
GCC parallel::stable_sort - time :10.4285 seconds
cntree::parallel_stable_sort - time :10.676 seconds

Equal elements --------------------------------------------------
GCC std::sort - time :13.4256 seconds
cntree::intro_sort - time :14.7292 seconds
GCC parallel::sort - time :3.89241 seconds 
tbb::parallel_sort - time :0.116944 seconds
cntree::parallel_sort - time :3.58016 seconds

GCC std::stable_sort - time :17.4644 seconds
cntree::stable_sort - time :21.592 seconds
GCC parallel::stable_sort - time :9.7224 seconds
cntree::parallel_stable_sort - time :5.85915 seconds