code: private void pushRun(int runBase, int runLen) {
          this.runBase[stackSize] = runBase;
          this.runLen[stackSize] = runLen;
          stackSize++;
      }
docs: Pushes the specified run onto the pending-run stack.
  
  @param runBase index of the first element in the run
  @param runLen  the number of elements in the run