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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam <cannam@all-day-breakfast.com>
date Tue, 19 Nov 2019 14:52:55 +0000
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25 <title>FFTW 3.3.8: Wisdom Generic Export/Import from Fortran</title>
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71 <a name="Wisdom-Generic-Export_002fImport-from-Fortran"></a>
72 <div class="header">
73 <p>
74 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>
75 </div>
76 <hr>
77 <a name="Wisdom-Generic-Export_002fImport-from-Fortran-1"></a>
78 <h4 class="subsection">7.6.3 Wisdom Generic Export/Import from Fortran</h4>
79
80 <p>The most generic wisdom export/import functions allow you to provide
81 an arbitrary callback function to read/write one character at a time
82 in any way you want. However, your callback function must be written
83 in a special way, using the <code>bind(C)</code> attribute to be passed to a
84 C interface.
85 </p>
86 <a name="index-fftw_005fexport_005fwisdom-1"></a>
87 <p>In particular, to call the generic wisdom export function
88 <code>fftw_export_wisdom</code>, you would write a callback subroutine of the form:
89 </p>
90 <div class="example">
91 <pre class="example"> subroutine my_write_char(c, p) bind(C)
92 use, intrinsic :: iso_c_binding
93 character(C_CHAR), value :: c
94 type(C_PTR), value :: p
95 <em>...write c...</em>
96 end subroutine my_write_char
97 </pre></div>
98
99 <p>Given such a subroutine (along with the corresponding interface definition), you could then export wisdom using:
100 </p>
101 <a name="index-c_005ffunloc"></a>
102 <div class="example">
103 <pre class="example"> call fftw_export_wisdom(c_funloc(my_write_char), p)
104 </pre></div>
105
106 <a name="index-c_005floc"></a>
107 <a name="index-c_005ff_005fpointer-4"></a>
108 <p>The standard <code>c_funloc</code> intrinsic converts a Fortran
109 <code>bind(C)</code> subroutine into a C function pointer. The parameter
110 <code>p</code> is a <code>type(C_PTR)</code> to any arbitrary data that you want
111 to pass to <code>my_write_char</code> (or <code>C_NULL_PTR</code> if none). (Note
112 that you can get a C pointer to Fortran data using the intrinsic
113 <code>c_loc</code>, and convert it back to a Fortran pointer in
114 <code>my_write_char</code> using <code>c_f_pointer</code>.)
115 </p>
116 <p>Similarly, to use the generic <code>fftw_import_wisdom</code>, you would
117 define a callback function of the form:
118 </p>
119 <a name="index-fftw_005fimport_005fwisdom-1"></a>
120 <div class="example">
121 <pre class="example"> integer(C_INT) function my_read_char(p) bind(C)
122 use, intrinsic :: iso_c_binding
123 type(C_PTR), value :: p
124 character :: c
125 <em>...read a character c...</em>
126 my_read_char = ichar(c, C_INT)
127 end function my_read_char
128
129 ....
130
131 integer(C_INT) :: ret
132 ret = fftw_import_wisdom(c_funloc(my_read_char), p)
133 if (ret .eq. 0) stop 'error importing wisdom'
134 </pre></div>
135
136 <p>Your function can return <code>-1</code> if the end of the input is reached.
137 Again, <code>p</code> is an arbitrary <code>type(C_PTR</code> that is passed
138 through to your function. <code>fftw_import_wisdom</code> returns <code>0</code>
139 if an error occurred and nonzero otherwise.
140 </p>
141 <hr>
142 <div class="header">
143 <p>
144 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>
145 </div>
146
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148
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