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Current fftw source
author Chris Cannam
date Tue, 18 Oct 2016 13:40:26 +0100
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Chris@42 24 <head>
Chris@42 25 <title>FFTW 3.3.5: Wisdom Generic Export/Import from Fortran</title>
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Chris@42 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
Chris@42 72 <a name="Wisdom-Generic-Export_002fImport-from-Fortran"></a>
Chris@42 73 <div class="header">
Chris@42 74 <p>
Chris@42 75 Previous: <a href="Wisdom-String-Export_002fImport-from-Fortran.html#Wisdom-String-Export_002fImport-from-Fortran" accesskey="p" rel="prev">Wisdom String Export/Import from Fortran</a>, Up: <a href="Accessing-the-wisdom-API-from-Fortran.html#Accessing-the-wisdom-API-from-Fortran" accesskey="u" rel="up">Accessing the wisdom API from Fortran</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
Chris@42 76 </div>
Chris@42 77 <hr>
Chris@42 78 <a name="Wisdom-Generic-Export_002fImport-from-Fortran-1"></a>
Chris@42 79 <h4 class="subsection">7.6.3 Wisdom Generic Export/Import from Fortran</h4>
Chris@42 80
Chris@42 81 <p>The most generic wisdom export/import functions allow you to provide
Chris@42 82 an arbitrary callback function to read/write one character at a time
Chris@42 83 in any way you want. However, your callback function must be written
Chris@42 84 in a special way, using the <code>bind(C)</code> attribute to be passed to a
Chris@42 85 C interface.
Chris@42 86 </p>
Chris@42 87 <a name="index-fftw_005fexport_005fwisdom-1"></a>
Chris@42 88 <p>In particular, to call the generic wisdom export function
Chris@42 89 <code>fftw_export_wisdom</code>, you would write a callback subroutine of the form:
Chris@42 90 </p>
Chris@42 91 <div class="example">
Chris@42 92 <pre class="example"> subroutine my_write_char(c, p) bind(C)
Chris@42 93 use, intrinsic :: iso_c_binding
Chris@42 94 character(C_CHAR), value :: c
Chris@42 95 type(C_PTR), value :: p
Chris@42 96 <em>...write c...</em>
Chris@42 97 end subroutine my_write_char
Chris@42 98 </pre></div>
Chris@42 99
Chris@42 100 <p>Given such a subroutine (along with the corresponding interface definition), you could then export wisdom using:
Chris@42 101 </p>
Chris@42 102 <a name="index-c_005ffunloc"></a>
Chris@42 103 <div class="example">
Chris@42 104 <pre class="example"> call fftw_export_wisdom(c_funloc(my_write_char), p)
Chris@42 105 </pre></div>
Chris@42 106
Chris@42 107 <a name="index-c_005floc"></a>
Chris@42 108 <a name="index-c_005ff_005fpointer-4"></a>
Chris@42 109 <p>The standard <code>c_funloc</code> intrinsic converts a Fortran
Chris@42 110 <code>bind(C)</code> subroutine into a C function pointer. The parameter
Chris@42 111 <code>p</code> is a <code>type(C_PTR)</code> to any arbitrary data that you want
Chris@42 112 to pass to <code>my_write_char</code> (or <code>C_NULL_PTR</code> if none). (Note
Chris@42 113 that you can get a C pointer to Fortran data using the intrinsic
Chris@42 114 <code>c_loc</code>, and convert it back to a Fortran pointer in
Chris@42 115 <code>my_write_char</code> using <code>c_f_pointer</code>.)
Chris@42 116 </p>
Chris@42 117 <p>Similarly, to use the generic <code>fftw_import_wisdom</code>, you would
Chris@42 118 define a callback function of the form:
Chris@42 119 </p>
Chris@42 120 <a name="index-fftw_005fimport_005fwisdom-1"></a>
Chris@42 121 <div class="example">
Chris@42 122 <pre class="example"> integer(C_INT) function my_read_char(p) bind(C)
Chris@42 123 use, intrinsic :: iso_c_binding
Chris@42 124 type(C_PTR), value :: p
Chris@42 125 character :: c
Chris@42 126 <em>...read a character c...</em>
Chris@42 127 my_read_char = ichar(c, C_INT)
Chris@42 128 end function my_read_char
Chris@42 129
Chris@42 130 ....
Chris@42 131
Chris@42 132 integer(C_INT) :: ret
Chris@42 133 ret = fftw_import_wisdom(c_funloc(my_read_char), p)
Chris@42 134 if (ret .eq. 0) stop 'error importing wisdom'
Chris@42 135 </pre></div>
Chris@42 136
Chris@42 137 <p>Your function can return <code>-1</code> if the end of the input is reached.
Chris@42 138 Again, <code>p</code> is an arbitrary <code>type(C_PTR</code> that is passed
Chris@42 139 through to your function. <code>fftw_import_wisdom</code> returns <code>0</code>
Chris@42 140 if an error occurred and nonzero otherwise.
Chris@42 141 </p>
Chris@42 142 <hr>
Chris@42 143 <div class="header">
Chris@42 144 <p>
Chris@42 145 Previous: <a href="Wisdom-String-Export_002fImport-from-Fortran.html#Wisdom-String-Export_002fImport-from-Fortran" accesskey="p" rel="prev">Wisdom String Export/Import from Fortran</a>, Up: <a href="Accessing-the-wisdom-API-from-Fortran.html#Accessing-the-wisdom-API-from-Fortran" accesskey="u" rel="up">Accessing the wisdom API from Fortran</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
Chris@42 146 </div>
Chris@42 147
Chris@42 148
Chris@42 149
Chris@42 150 </body>
Chris@42 151 </html>