インテル® Fortran コンパイラー XE 13.1 ユーザー・リファレンス・ガイド
Portability Function: Returns the elapsed time in seconds since the start of the current process.
The result type is REAL(8). This routine provides accurate timing to the nearest millisecond (Windows* OS) or to the nearest microsecond (Linux* OS and OS X*), taking into account the frequency of the processor where the current process is running.
Note that the first call to DCLOCK performs calibration.