Returns the number of clock ticks since the start of the process.
Supported on systems with @code{clock(3)} (q.v.).
+@emph{Warning:} this intrinsic does not increase the range
+of the timing values over that returned by @code{clock(3)}.
+On a system with a 32-bit @code{clock(3)},
+@code{@0@} will return a 32-bit value,
+even though converted to an @samp{INTEGER(KIND=2)} value.
+That means overflows of the 32-bit value can still occur.
+
No Fortran implementations other than GNU Fortran are
known to support this intrinsic at the time of this
writing.
This value is suitable for passing to @code{CTIME},
@code{GMTIME}, and @code{LTIME}.
+@emph{Warning:} this intrinsic does not increase the range
+of the timing values over that returned by @code{time(3)}.
+On a system with a 32-bit @code{time(3)},
+@code{@0@} will return a 32-bit value,
+even though converted to an @samp{INTEGER(KIND=2)} value.
+That means overflows of the 32-bit value can still occur.
+
No Fortran implementations other than GNU Fortran are
known to support this intrinsic at the time of this
writing.