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| <title>The GNU Fortran Compiler: _gfortran_caf_co_reduce</title> |
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| <a name="g_t_005fgfortran_005fcaf_005fco_005freduce-_002d_002d_002d-Generic-collective-reduction"></a> |
| <h4 class="subsection">8.2.25 <code>_gfortran_caf_co_reduce</code> — Generic collective reduction</h4> |
| <a name="index-Coarray_002c-_005fgfortran_005fcaf_005fco_005freduce"></a> |
| |
| <dl compact="compact"> |
| <dt><em>Description</em>:</dt> |
| <dd><p>Calculates the for the each array element of the variable <var>a</var> the reduction |
| value for that element in the current team; if <var>result_image</var> has the |
| value 0, the result shall be stored on all images, otherwise, only on the |
| specified image. The <var>opr</var> is a pure function doing a mathematically |
| commutative and associative operation. |
| </p> |
| <p>The <var>opr_flags</var> denote the following; the values are bitwise ored. |
| <code>GFC_CAF_BYREF</code> (1) if the result should be returned |
| by value; <code>GFC_CAF_HIDDENLEN</code> (2) whether the result and argument |
| string lengths shall be specified as hidden argument; |
| <code>GFC_CAF_ARG_VALUE</code> (4) whether the arguments shall be passed by value, |
| <code>GFC_CAF_ARG_DESC</code> (8) whether the arguments shall be passed by descriptor. |
| </p> |
| |
| </dd> |
| <dt><em>Syntax</em>:</dt> |
| <dd><p><code>void _gfortran_caf_co_reduce (gfc_descriptor_t *a, |
| void * (*opr) (void *, void *), int opr_flags, int result_image, |
| int *stat, char *errmsg, int a_len, int errmsg_len)</code> |
| </p> |
| </dd> |
| <dt><em>Arguments</em>:</dt> |
| <dd><table> |
| <tr><td width="15%"><var>opr</var></td><td width="70%">Function pointer to the reduction function.</td></tr> |
| <tr><td width="15%"><var>opr_flags</var></td><td width="70%">Flags regarding the reduction function</td></tr> |
| <tr><td width="15%"><var>a</var></td><td width="70%">intent(inout) And array descriptor with the data to be |
| breoadcasted (on <var>source_image</var>) or to be received (other images).</td></tr> |
| <tr><td width="15%"><var>result_image</var></td><td width="70%">The ID of the image to which the reduced |
| value should be copied to; if zero, it has to be copied to all images.</td></tr> |
| <tr><td width="15%"><var>stat</var></td><td width="70%">intent(out) Stores the status STAT= and may be NULL.</td></tr> |
| <tr><td width="15%"><var>errmsg</var></td><td width="70%">intent(out) When an error occurs, this will be set to |
| an error message; may be NULL</td></tr> |
| <tr><td width="15%"><var>a_len</var></td><td width="70%">The string length of argument <var>a</var>.</td></tr> |
| <tr><td width="15%"><var>errmsg_len</var></td><td width="70%">the buffer size of errmsg.</td></tr> |
| </table> |
| |
| </dd> |
| <dt><em>NOTES</em></dt> |
| <dd><p>If <var>result_image</var> is nonzero, the value on all images except of the |
| specified one become undefined; hence, the library may make use of this. |
| For character arguments, the result is passed as first argument, followed |
| by the result string length, next come the two string arguments, followed |
| by the two hidden arguments. With C binding, there are no hidden arguments |
| and by-reference passing and either only a single character is passed or |
| an array descriptor. |
| </p></dd> |
| </dl> |
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