partitioning.cpp

// *__m is median. partition [__first, __m) < *__m and
// *__m <= [__m, __last)
//
// Special handling for almost sorted targets
while (true) {
  while (__comp(*++__i, *__m));
  while (!__comp(*--__j, *__m));
  if (__i > __j) break;
  swap(*__i, *__j);
}
swap(*__i, *__m);