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<title>The GNU Fortran Compiler: _gfortran_caf_co_reduce</title>
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Previous: <a href="_005fgfortran_005fcaf_005fco_005fsum.html#g_t_005fgfortran_005fcaf_005fco_005fsum" accesskey="p" rel="prev">_gfortran_caf_co_sum</a>, Up: <a href="Function-ABI-Documentation.html#Function-ABI-Documentation" accesskey="u" rel="up">Function ABI Documentation</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<a name="g_t_005fgfortran_005fcaf_005fco_005freduce-_002d_002d_002d-Generic-collective-reduction"></a>
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<h4 class="subsection">8.2.36 <code>_gfortran_caf_co_reduce</code> — Generic collective reduction</h4>
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<a name="index-Coarray_002c-_005fgfortran_005fcaf_005fco_005freduce"></a>
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<dl compact="compact">
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<dt><em>Description</em>:</dt>
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<dd><p>Calculates for each array element of the variable <var>a</var> the reduction
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value for that element in the current team; if <var>result_image</var> has the
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value 0, the result shall be stored on all images, otherwise, only on the
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specified image. The <var>opr</var> is a pure function doing a mathematically
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commutative and associative operation.
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</p>
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<p>The <var>opr_flags</var> denote the following; the values are bitwise ored.
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<code>GFC_CAF_BYREF</code> (1) if the result should be returned
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by reference; <code>GFC_CAF_HIDDENLEN</code> (2) whether the result and argument
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string lengths shall be specified as hidden arguments;
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<code>GFC_CAF_ARG_VALUE</code> (4) whether the arguments shall be passed by value,
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<code>GFC_CAF_ARG_DESC</code> (8) whether the arguments shall be passed by descriptor.
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</p>
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</dd>
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<dt><em>Syntax</em>:</dt>
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<dd><p><code>void _gfortran_caf_co_reduce (gfc_descriptor_t *a,
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void * (*opr) (void *, void *), int opr_flags, int result_image,
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int *stat, char *errmsg, int a_len, int errmsg_len)</code>
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</p>
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</dd>
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<dt><em>Arguments</em>:</dt>
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<dd><table>
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<tr><td width="15%"><var>a</var></td><td width="70%">intent(inout) An array descriptor with the data to be
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processed. On the destination image(s) the result overwrites the old content.</td></tr>
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<tr><td width="15%"><var>opr</var></td><td width="70%">intent(in) Function pointer to the reduction function</td></tr>
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<tr><td width="15%"><var>opr_flags</var></td><td width="70%">intent(in) Flags regarding the reduction function</td></tr>
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<tr><td width="15%"><var>result_image</var></td><td width="70%">intent(in) The ID of the image to which the
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reduced value should be copied to; if zero, it has to be copied to all images.</td></tr>
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<tr><td width="15%"><var>stat</var></td><td width="70%">intent(out) Stores the status STAT= and may be NULL.</td></tr>
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<tr><td width="15%"><var>errmsg</var></td><td width="70%">intent(out) When an error occurs, this will be set to
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an error message; may be NULL.</td></tr>
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<tr><td width="15%"><var>a_len</var></td><td width="70%">intent(in) the string length of argument <var>a</var></td></tr>
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<tr><td width="15%"><var>errmsg_len</var></td><td width="70%">intent(in) the buffer size of errmsg</td></tr>
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</table>
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</dd>
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<dt><em>NOTES</em></dt>
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<dd><p>If <var>result_image</var> is nonzero, the data in the array descriptor <var>a</var> on
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all images except of the specified one become undefined; hence, the library may
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make use of this.
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</p>
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<p>For character arguments, the result is passed as first argument, followed
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by the result string length, next come the two string arguments, followed
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by the two hidden string length arguments. With C binding, there are no hidden
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arguments and by-reference passing and either only a single character is passed
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or an array descriptor.
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</p></dd>
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</dl>
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Previous: <a href="_005fgfortran_005fcaf_005fco_005fsum.html#g_t_005fgfortran_005fcaf_005fco_005fsum" accesskey="p" rel="prev">_gfortran_caf_co_sum</a>, Up: <a href="Function-ABI-Documentation.html#Function-ABI-Documentation" accesskey="u" rel="up">Function ABI Documentation</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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