mirror of
https://github.com/tildearrow/furnace.git
synced 2024-11-06 04:45:05 +00:00
281 lines
15 KiB
HTML
281 lines
15 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<!-- This manual is for FFTW
|
|
(version 3.3.10, 10 December 2020).
|
|
|
|
Copyright (C) 2003 Matteo Frigo.
|
|
|
|
Copyright (C) 2003 Massachusetts Institute of Technology.
|
|
|
|
Permission is granted to make and distribute verbatim copies of this
|
|
manual provided the copyright notice and this permission notice are
|
|
preserved on all copies.
|
|
|
|
Permission is granted to copy and distribute modified versions of this
|
|
manual under the conditions for verbatim copying, provided that the
|
|
entire resulting derived work is distributed under the terms of a
|
|
permission notice identical to this one.
|
|
|
|
Permission is granted to copy and distribute translations of this manual
|
|
into another language, under the above conditions for modified versions,
|
|
except that this permission notice may be stated in a translation
|
|
approved by the Free Software Foundation. -->
|
|
<!-- Created by GNU Texinfo 6.7, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<title>Upgrading from FFTW version 2 (FFTW 3.3.10)</title>
|
|
|
|
<meta name="description" content="Upgrading from FFTW version 2 (FFTW 3.3.10)">
|
|
<meta name="keywords" content="Upgrading from FFTW version 2 (FFTW 3.3.10)">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content="makeinfo">
|
|
<link href="index.html" rel="start" title="Top">
|
|
<link href="Concept-Index.html" rel="index" title="Concept Index">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="index.html" rel="up" title="Top">
|
|
<link href="Installation-and-Customization.html" rel="next" title="Installation and Customization">
|
|
<link href="Wisdom-of-Fortran_003f.html" rel="prev" title="Wisdom of Fortran?">
|
|
<style type="text/css">
|
|
<!--
|
|
a.summary-letter {text-decoration: none}
|
|
blockquote.indentedblock {margin-right: 0em}
|
|
div.display {margin-left: 3.2em}
|
|
div.example {margin-left: 3.2em}
|
|
div.lisp {margin-left: 3.2em}
|
|
kbd {font-style: oblique}
|
|
pre.display {font-family: inherit}
|
|
pre.format {font-family: inherit}
|
|
pre.menu-comment {font-family: serif}
|
|
pre.menu-preformatted {font-family: serif}
|
|
span.nolinebreak {white-space: nowrap}
|
|
span.roman {font-family: initial; font-weight: normal}
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
|
ul.no-bullet {list-style: none}
|
|
-->
|
|
</style>
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en">
|
|
<span id="Upgrading-from-FFTW-version-2"></span><div class="header">
|
|
<p>
|
|
Next: <a href="Installation-and-Customization.html" accesskey="n" rel="next">Installation and Customization</a>, Previous: <a href="Calling-FFTW-from-Legacy-Fortran.html" accesskey="p" rel="prev">Calling FFTW from Legacy Fortran</a>, Up: <a href="index.html" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
<hr>
|
|
<span id="Upgrading-from-FFTW-version-2-1"></span><h2 class="chapter">9 Upgrading from FFTW version 2</h2>
|
|
|
|
<p>In this chapter, we outline the process for updating codes designed for
|
|
the older FFTW 2 interface to work with FFTW 3. The interface for FFTW
|
|
3 is not backwards-compatible with the interface for FFTW 2 and earlier
|
|
versions; codes written to use those versions will fail to link with
|
|
FFTW 3. Nor is it possible to write “compatibility wrappers” to
|
|
bridge the gap (at least not efficiently), because FFTW 3 has different
|
|
semantics from previous versions. However, upgrading should be a
|
|
straightforward process because the data formats are identical and the
|
|
overall style of planning/execution is essentially the same.
|
|
</p>
|
|
<p>Unlike FFTW 2, there are no separate header files for real and complex
|
|
transforms (or even for different precisions) in FFTW 3; all interfaces
|
|
are defined in the <code><fftw3.h></code> header file.
|
|
</p>
|
|
<span id="Numeric-Types"></span><h3 class="heading">Numeric Types</h3>
|
|
|
|
<p>The main difference in data types is that <code>fftw_complex</code> in FFTW 2
|
|
was defined as a <code>struct</code> with macros <code>c_re</code> and <code>c_im</code>
|
|
for accessing the real/imaginary parts. (This is binary-compatible with
|
|
FFTW 3 on any machine except perhaps for some older Crays in single
|
|
precision.) The equivalent macros for FFTW 3 are:
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example">#define c_re(c) ((c)[0])
|
|
#define c_im(c) ((c)[1])
|
|
</pre></div>
|
|
|
|
<p>This does not work if you are using the C99 complex type, however,
|
|
unless you insert a <code>double*</code> typecast into the above macros
|
|
(see <a href="Complex-numbers.html">Complex numbers</a>).
|
|
</p>
|
|
<p>Also, FFTW 2 had an <code>fftw_real</code> typedef that was an alias for
|
|
<code>double</code> (in double precision). In FFTW 3 you should just use
|
|
<code>double</code> (or whatever precision you are employing).
|
|
</p>
|
|
<span id="Plans"></span><h3 class="heading">Plans</h3>
|
|
|
|
<p>The major difference between FFTW 2 and FFTW 3 is in the
|
|
planning/execution division of labor. In FFTW 2, plans were found for a
|
|
given transform size and type, and then could be applied to <em>any</em>
|
|
arrays and for <em>any</em> multiplicity/stride parameters. In FFTW 3,
|
|
you specify the particular arrays, stride parameters, etcetera when
|
|
creating the plan, and the plan is then executed for <em>those</em> arrays
|
|
(unless the guru interface is used) and <em>those</em> parameters
|
|
<em>only</em>. (FFTW 2 had “specific planner” routines that planned for
|
|
a particular array and stride, but the plan could still be used for
|
|
other arrays and strides.) That is, much of the information that was
|
|
formerly specified at execution time is now specified at planning time.
|
|
</p>
|
|
<p>Like FFTW 2’s specific planner routines, the FFTW 3 planner overwrites
|
|
the input/output arrays unless you use <code>FFTW_ESTIMATE</code>.
|
|
</p>
|
|
<p>FFTW 2 had separate data types <code>fftw_plan</code>, <code>fftwnd_plan</code>,
|
|
<code>rfftw_plan</code>, and <code>rfftwnd_plan</code> for complex and real one- and
|
|
multi-dimensional transforms, and each type had its own ‘<samp>destroy</samp>’
|
|
function. In FFTW 3, all plans are of type <code>fftw_plan</code> and all are
|
|
destroyed by <code>fftw_destroy_plan(plan)</code>.
|
|
</p>
|
|
<p>Where you formerly used <code>fftw_create_plan</code> and <code>fftw_one</code> to
|
|
plan and compute a single 1d transform, you would now use
|
|
<code>fftw_plan_dft_1d</code> to plan the transform. If you used the generic
|
|
<code>fftw</code> function to execute the transform with multiplicity
|
|
(<code>howmany</code>) and stride parameters, you would now use the advanced
|
|
interface <code>fftw_plan_many_dft</code> to specify those parameters. The
|
|
plans are now executed with <code>fftw_execute(plan)</code>, which takes all
|
|
of its parameters (including the input/output arrays) from the plan.
|
|
</p>
|
|
<p>In-place transforms no longer interpret their output argument as scratch
|
|
space, nor is there an <code>FFTW_IN_PLACE</code> flag. You simply pass the
|
|
same pointer for both the input and output arguments. (Previously, the
|
|
output <code>ostride</code> and <code>odist</code> parameters were ignored for
|
|
in-place transforms; now, if they are specified via the advanced
|
|
interface, they are significant even in the in-place case, although they
|
|
should normally equal the corresponding input parameters.)
|
|
</p>
|
|
<p>The <code>FFTW_ESTIMATE</code> and <code>FFTW_MEASURE</code> flags have the same
|
|
meaning as before, although the planning time will differ. You may also
|
|
consider using <code>FFTW_PATIENT</code>, which is like <code>FFTW_MEASURE</code>
|
|
except that it takes more time in order to consider a wider variety of
|
|
algorithms.
|
|
</p>
|
|
<p>For multi-dimensional complex DFTs, instead of <code>fftwnd_create_plan</code>
|
|
(or <code>fftw2d_create_plan</code> or <code>fftw3d_create_plan</code>), followed by
|
|
<code>fftwnd_one</code>, you would use <code>fftw_plan_dft</code> (or
|
|
<code>fftw_plan_dft_2d</code> or <code>fftw_plan_dft_3d</code>). followed by
|
|
<code>fftw_execute</code>. If you used <code>fftwnd</code> to to specify strides
|
|
etcetera, you would instead specify these via <code>fftw_plan_many_dft</code>.
|
|
</p>
|
|
<p>The analogues to <code>rfftw_create_plan</code> and <code>rfftw_one</code> with
|
|
<code>FFTW_REAL_TO_COMPLEX</code> or <code>FFTW_COMPLEX_TO_REAL</code> directions
|
|
are <code>fftw_plan_r2r_1d</code> with kind <code>FFTW_R2HC</code> or
|
|
<code>FFTW_HC2R</code>, followed by <code>fftw_execute</code>. The stride etcetera
|
|
arguments of <code>rfftw</code> are now in <code>fftw_plan_many_r2r</code>.
|
|
</p>
|
|
<p>Instead of <code>rfftwnd_create_plan</code> (or <code>rfftw2d_create_plan</code> or
|
|
<code>rfftw3d_create_plan</code>) followed by
|
|
<code>rfftwnd_one_real_to_complex</code> or
|
|
<code>rfftwnd_one_complex_to_real</code>, you now use <code>fftw_plan_dft_r2c</code>
|
|
(or <code>fftw_plan_dft_r2c_2d</code> or <code>fftw_plan_dft_r2c_3d</code>) or
|
|
<code>fftw_plan_dft_c2r</code> (or <code>fftw_plan_dft_c2r_2d</code> or
|
|
<code>fftw_plan_dft_c2r_3d</code>), respectively, followed by
|
|
<code>fftw_execute</code>. As usual, the strides etcetera of
|
|
<code>rfftwnd_real_to_complex</code> or <code>rfftwnd_complex_to_real</code> are no
|
|
specified in the advanced planner routines,
|
|
<code>fftw_plan_many_dft_r2c</code> or <code>fftw_plan_many_dft_c2r</code>.
|
|
</p>
|
|
<span id="Wisdom-2"></span><h3 class="heading">Wisdom</h3>
|
|
|
|
<p>In FFTW 2, you had to supply the <code>FFTW_USE_WISDOM</code> flag in order to
|
|
use wisdom; in FFTW 3, wisdom is always used. (You could simulate the
|
|
FFTW 2 wisdom-less behavior by calling <code>fftw_forget_wisdom</code> after
|
|
every planner call.)
|
|
</p>
|
|
<p>The FFTW 3 wisdom import/export routines are almost the same as before
|
|
(although the storage format is entirely different). There is one
|
|
significant difference, however. In FFTW 2, the import routines would
|
|
never read past the end of the wisdom, so you could store extra data
|
|
beyond the wisdom in the same file, for example. In FFTW 3, the
|
|
file-import routine may read up to a few hundred bytes past the end of
|
|
the wisdom, so you cannot store other data just beyond it.<a id="DOCF11" href="#FOOT11"><sup>11</sup></a>
|
|
</p>
|
|
<p>Wisdom has been enhanced by additional humility in FFTW 3: whereas FFTW
|
|
2 would re-use wisdom for a given transform size regardless of the
|
|
stride etc., in FFTW 3 wisdom is only used with the strides etc. for
|
|
which it was created. Unfortunately, this means FFTW 3 has to create
|
|
new plans from scratch more often than FFTW 2 (in FFTW 2, planning
|
|
e.g. one transform of size 1024 also created wisdom for all smaller
|
|
powers of 2, but this no longer occurs).
|
|
</p>
|
|
<p>FFTW 3 also has the new routine <code>fftw_import_system_wisdom</code> to
|
|
import wisdom from a standard system-wide location.
|
|
</p>
|
|
<span id="Memory-allocation"></span><h3 class="heading">Memory allocation</h3>
|
|
|
|
<p>In FFTW 3, we recommend allocating your arrays with <code>fftw_malloc</code>
|
|
and deallocating them with <code>fftw_free</code>; this is not required, but
|
|
allows optimal performance when SIMD acceleration is used. (Those two
|
|
functions actually existed in FFTW 2, and worked the same way, but were
|
|
not documented.)
|
|
</p>
|
|
<p>In FFTW 2, there were <code>fftw_malloc_hook</code> and <code>fftw_free_hook</code>
|
|
functions that allowed the user to replace FFTW’s memory-allocation
|
|
routines (e.g. to implement different error-handling, since by default
|
|
FFTW prints an error message and calls <code>exit</code> to abort the program
|
|
if <code>malloc</code> returns <code>NULL</code>). These hooks are not supported in
|
|
FFTW 3; those few users who require this functionality can just
|
|
directly modify the memory-allocation routines in FFTW (they are defined
|
|
in <code>kernel/alloc.c</code>).
|
|
</p>
|
|
<span id="Fortran-interface"></span><h3 class="heading">Fortran interface</h3>
|
|
|
|
<p>In FFTW 2, the subroutine names were obtained by replacing ‘<samp>fftw_</samp>’
|
|
with ‘<samp>fftw_f77</samp>’; in FFTW 3, you replace ‘<samp>fftw_</samp>’ with
|
|
‘<samp>dfftw_</samp>’ (or ‘<samp>sfftw_</samp>’ or ‘<samp>lfftw_</samp>’, depending upon the
|
|
precision).
|
|
</p>
|
|
<p>In FFTW 3, we have begun recommending that you always declare the type
|
|
used to store plans as <code>integer*8</code>. (Too many people didn’t notice
|
|
our instruction to switch from <code>integer</code> to <code>integer*8</code> for
|
|
64-bit machines.)
|
|
</p>
|
|
<p>In FFTW 3, we provide a <code>fftw3.f</code> “header file” to include in
|
|
your code (and which is officially installed on Unix systems). (In FFTW
|
|
2, we supplied a <code>fftw_f77.i</code> file, but it was not installed.)
|
|
</p>
|
|
<p>Otherwise, the C-Fortran interface relationship is much the same as it
|
|
was before (e.g. return values become initial parameters, and
|
|
multi-dimensional arrays are in column-major order). Unlike FFTW 2, we
|
|
do provide some support for wisdom import/export in Fortran
|
|
(see <a href="Wisdom-of-Fortran_003f.html">Wisdom of Fortran?</a>).
|
|
</p>
|
|
<span id="Threads"></span><h3 class="heading">Threads</h3>
|
|
|
|
<p>Like FFTW 2, only the execution routines are thread-safe. All planner
|
|
routines, etcetera, should be called by only a single thread at a time
|
|
(see <a href="Thread-safety.html">Thread safety</a>). <em>Unlike</em> FFTW 2, there is no special
|
|
<code>FFTW_THREADSAFE</code> flag for the planner to allow a given plan to be
|
|
usable by multiple threads in parallel; this is now the case by default.
|
|
</p>
|
|
<p>The multi-threaded version of FFTW 2 required you to pass the number of
|
|
threads each time you execute the transform. The number of threads is
|
|
now stored in the plan, and is specified before the planner is called by
|
|
<code>fftw_plan_with_nthreads</code>. The threads initialization routine used
|
|
to be called <code>fftw_threads_init</code> and would return zero on success;
|
|
the new routine is called <code>fftw_init_threads</code> and returns zero on
|
|
failure. The current number of threads used by the planner can be
|
|
checked with <code>fftw_planner_nthreads</code>. See <a href="Multi_002dthreaded-FFTW.html">Multi-threaded FFTW</a>.
|
|
</p>
|
|
<p>There is no separate threads header file in FFTW 3; all the function
|
|
prototypes are in <code><fftw3.h></code>. However, you still have to link to
|
|
a separate library (<code>-lfftw3_threads -lfftw3 -lm</code> on Unix), as well as
|
|
to the threading library (e.g. POSIX threads on Unix).
|
|
</p>
|
|
<div class="footnote">
|
|
<hr>
|
|
<h4 class="footnotes-heading">Footnotes</h4>
|
|
|
|
<h5><a id="FOOT11" href="#DOCF11">(11)</a></h3>
|
|
<p>We
|
|
do our own buffering because GNU libc I/O routines are horribly slow for
|
|
single-character I/O, apparently for thread-safety reasons (whether you
|
|
are using threads or not).</p>
|
|
</div>
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Installation-and-Customization.html" accesskey="n" rel="next">Installation and Customization</a>, Previous: <a href="Calling-FFTW-from-Legacy-Fortran.html" accesskey="p" rel="prev">Calling FFTW from Legacy Fortran</a>, Up: <a href="index.html" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|