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| <title>The GNU Fortran Compiler: DTIME</title> |
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| <a name="DTIME-_002d_002d_002d-Execution-time-subroutine-_0028or-function_0029"></a> |
| <h3 class="section">8.71 <code>DTIME</code> — Execution time subroutine (or function)</h3> |
| <a name="index-DTIME"></a> |
| <a name="index-time_002c-elapsed-1"></a> |
| <a name="index-elapsed-time"></a> |
| |
| <dl compact="compact"> |
| <dt><em>Description</em>:</dt> |
| <dd><p><code>DTIME(VALUES, TIME)</code> initially returns the number of seconds of runtime |
| since the start of the process’s execution in <var>TIME</var>. <var>VALUES</var> |
| returns the user and system components of this time in <code>VALUES(1)</code> and |
| <code>VALUES(2)</code> respectively. <var>TIME</var> is equal to <code>VALUES(1) + |
| VALUES(2)</code>. |
| </p> |
| <p>Subsequent invocations of <code>DTIME</code> return values accumulated since the |
| previous invocation. |
| </p> |
| <p>On some systems, the underlying timings are represented using types with |
| sufficiently small limits that overflows (wrap around) are possible, such as |
| 32-bit types. Therefore, the values returned by this intrinsic might be, or |
| become, negative, or numerically less than previous values, during a single |
| run of the compiled program. |
| </p> |
| <p>Please note, that this implementation is thread safe if used within OpenMP |
| directives, i.e., its state will be consistent while called from multiple |
| threads. However, if <code>DTIME</code> is called from multiple threads, the result |
| is still the time since the last invocation. This may not give the intended |
| results. If possible, use <code>CPU_TIME</code> instead. |
| </p> |
| <p>This intrinsic is provided in both subroutine and function forms; however, |
| only one form can be used in any given program unit. |
| </p> |
| <p><var>VALUES</var> and <var>TIME</var> are <code>INTENT(OUT)</code> and provide the following: |
| </p> |
| <table> |
| <tr><td width="15%"></td><td width="30%"><code>VALUES(1)</code>:</td><td width="40%">User time in seconds.</td></tr> |
| <tr><td width="15%"></td><td width="30%"><code>VALUES(2)</code>:</td><td width="40%">System time in seconds.</td></tr> |
| <tr><td width="15%"></td><td width="30%"><code>TIME</code>:</td><td width="40%">Run time since start in seconds.</td></tr> |
| </table> |
| |
| </dd> |
| <dt><em>Standard</em>:</dt> |
| <dd><p>GNU extension |
| </p> |
| </dd> |
| <dt><em>Class</em>:</dt> |
| <dd><p>Subroutine, function |
| </p> |
| </dd> |
| <dt><em>Syntax</em>:</dt> |
| <dd><table> |
| <tr><td width="80%"><code>CALL DTIME(VALUES, TIME)</code>.</td></tr> |
| <tr><td width="80%"><code>TIME = DTIME(VALUES)</code>, (not recommended).</td></tr> |
| </table> |
| |
| </dd> |
| <dt><em>Arguments</em>:</dt> |
| <dd><table> |
| <tr><td width="15%"><var>VALUES</var></td><td width="70%">The type shall be <code>REAL(4), DIMENSION(2)</code>.</td></tr> |
| <tr><td width="15%"><var>TIME</var></td><td width="70%">The type shall be <code>REAL(4)</code>.</td></tr> |
| </table> |
| |
| </dd> |
| <dt><em>Return value</em>:</dt> |
| <dd><p>Elapsed time in seconds since the last invocation or since the start of program |
| execution if not called before. |
| </p> |
| </dd> |
| <dt><em>Example</em>:</dt> |
| <dd><div class="smallexample"> |
| <pre class="smallexample">program test_dtime |
| integer(8) :: i, j |
| real, dimension(2) :: tarray |
| real :: result |
| call dtime(tarray, result) |
| print *, result |
| print *, tarray(1) |
| print *, tarray(2) |
| do i=1,100000000 ! Just a delay |
| j = i * i - i |
| end do |
| call dtime(tarray, result) |
| print *, result |
| print *, tarray(1) |
| print *, tarray(2) |
| end program test_dtime |
| </pre></div> |
| |
| </dd> |
| <dt><em>See also</em>:</dt> |
| <dd><p><a href="CPU_005fTIME.html#CPU_005fTIME">CPU_TIME</a> |
| </p> |
| </dd> |
| </dl> |
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