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<head><title>
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FFTW FAQ - Section 2
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</title>
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<link rev="made" href="mailto:fftw@fftw.org">
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<link rel="Contents" href="index.html">
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<link rel="Start" href="index.html">
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<link rel="Next" href="section3.html"><link rel="Previous" href="section1.html"><link rel="Bookmark" title="FFTW FAQ" href="index.html">
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</head><body text="#000000" bgcolor="#FFFFFF"><h1>
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FFTW FAQ - Section 2 <br>
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Installing FFTW
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</h1>
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<ul>
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<li><a href="#systems" rel=subdocument>Q2.1. Which systems does FFTW run on?</a>
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<li><a href="#runOnWindows" rel=subdocument>Q2.2. Does FFTW run on Windows?</a>
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<li><a href="#compilerCrashes" rel=subdocument>Q2.3. My compiler has trouble with FFTW.</a>
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<li><a href="#solarisSucks" rel=subdocument>Q2.4. FFTW does not compile on Solaris, complaining about
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<code>const</code>.</a>
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<li><a href="#3dnow" rel=subdocument>Q2.5. What's the difference between <code>--enable-3dnow</code> and <code>--enable-k7</code>?</a>
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<li><a href="#fma" rel=subdocument>Q2.6. What's the difference between the fma and the non-fma
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versions?</a>
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<li><a href="#languages" rel=subdocument>Q2.7. Which language is FFTW written in?</a>
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<li><a href="#fortran" rel=subdocument>Q2.8. Can I call FFTW from Fortran?</a>
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<li><a href="#cplusplus" rel=subdocument>Q2.9. Can I call FFTW from C++?</a>
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<li><a href="#whynotfortran" rel=subdocument>Q2.10. Why isn't FFTW written in Fortran/C++?</a>
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<li><a href="#singleprec" rel=subdocument>Q2.11. How do I compile FFTW to run in single precision?</a>
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<li><a href="#64bitk7" rel=subdocument>Q2.12. --enable-k7 does not work on x86-64</a>
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</ul><hr>
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<h2><A name="systems">
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Question 2.1. Which systems does FFTW run
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on?
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</A></h2>
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FFTW is written in ANSI C, and should work on any system with a decent
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C compiler. (See also <A href="#runOnWindows">Q2.2 `Does FFTW run on Windows?'</A>, <A href="#compilerCrashes">Q2.3 `My compiler has trouble with FFTW.'</A>.) FFTW can also take advantage of certain hardware-specific features,
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such as cycle counters and SIMD instructions, but this is optional.
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<h2><A name="runOnWindows">
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Question 2.2. Does FFTW run on Windows?
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</A></h2>
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Yes, many people have reported successfully using FFTW on Windows with
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various compilers. FFTW was not developed on Windows, but the source
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code is essentially straight ANSI C. See also the
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<A href="http://www.fftw.org/install/windows.html">FFTW Windows installation notes</A>, <A href="#compilerCrashes">Q2.3 `My compiler has trouble with FFTW.'</A>, and <A href="section3.html#vbetalia">Q3.18 `How do I call FFTW from the Microsoft language du
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jour?'</A>.
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<h2><A name="compilerCrashes">
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Question 2.3. My compiler has trouble with
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FFTW.
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</A></h2>
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Complain fiercely to the vendor of the compiler.
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<p>
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We have successfully used <code>gcc</code> 3.2.x on x86 and PPC, a recent Compaq C compiler for Alpha, version 6 of IBM's
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<code>xlc</code> compiler for AIX, Intel's <code>icc</code> versions 5-7, and Sun WorkShop <code>cc</code> version 6.
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<p>
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FFTW is likely to push compilers to their limits, however, and several
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compiler bugs have been exposed by FFTW. A partial list follows.
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<p>
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<code>gcc</code> 2.95.x for Solaris/SPARC produces incorrect code for
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the test program (workaround: recompile the
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<code>libbench2</code> directory with <code>-O2</code>).
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<p>
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NetBSD/macppc 1.6 comes with a <code>gcc</code> version that also miscompiles the test program. (Please report a workaround if you know
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one.)
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<p>
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<code>gcc</code> 3.2.3 for ARM reportedly crashes during compilation.
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This bug is reportedly fixed in later versions of
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<code>gcc</code>.
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<p>
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Versions 8.0 and 8.1 of Intel's <code>icc</code> falsely claim to be <code>gcc</code>, so you should specify <code>CC="icc -no-gcc"</code>; this is automatic in FFTW 3.1. <code>icc-8.0.066</code> reportely produces incorrect code for FFTW 2.1.5, but is fixed in version 8.1.
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<code>icc-7.1</code> compiler build 20030402Z appears to produce
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incorrect dependencies, causing the compilation to fail.
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<code>icc-7.1</code> build 20030307Z appears to work fine. (Use
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<code>icc -V</code> to check which build you have.) As of 2003/04/18,
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build 20030402Z appears not to be available any longer on Intel's
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website, whereas the older build 20030307Z is available.
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<p>
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<code>ranlib</code> of GNU <code>binutils</code> 2.9.1 on Irix has been observed to corrupt the FFTW libraries, causing a link failure when
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FFTW is compiled. Since <code>ranlib</code> is completely superfluous on Irix, we suggest deleting it from your system and replacing it with
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a symbolic link to <code>/bin/echo</code>.
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<p>
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If support for SIMD instructions is enabled in FFTW, further compiler
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problems may appear:
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<p>
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<code>gcc</code> 3.4.[0123] for x86 produces incorrect SSE2 code for
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FFTW when <code>-O2</code> (the best choice for FFTW) is used, causing
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FFTW to crash (<code>make check</code> crashes). This bug is fixed in <code>gcc</code> 3.4.4. On x86_64 (amd64/em64t), <code>gcc</code> 3.4.4 reportedly still has a similar problem, but this is fixed as of
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<code>gcc</code> 3.4.6.
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<p>
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<code>gcc-3.2</code> for x86 produces incorrect SIMD code if
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<code>-O3</code> is used. The same compiler produces incorrect SIMD
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code if no optimization is used, too. When using
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<code>gcc-3.2</code>, it is a good idea not to change the default
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<code>CFLAGS</code> selected by the <code>configure</code> script.
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<p>
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Some 3.0.x and 3.1.x versions of <code>gcc</code> on <code>x86</code> may crash. <code>gcc</code> so-called 2.96 shipping with RedHat 7.3 crashes
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when compiling SIMD code. In both cases, please upgrade to
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<code>gcc-3.2</code> or later.
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<p>
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Intel's <code>icc</code> 6.0 misaligns SSE constants, but FFTW has a
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workaround. <code>icc</code> 8.x fails to compile FFTW 3.0.x because it
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falsely claims to be <code>gcc</code>; we believe this to be a bug in <code>icc</code>, but FFTW 3.1 has a workaround.
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<p>
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Visual C++ 2003 reportedly produces incorrect code for SSE/SSE2 when
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compiling FFTW. This bug was reportedly fixed in VC++ 2005;
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alternatively, you could switch to the Intel compiler. VC++ 6.0 also
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reportedly produces incorrect code for the file
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<code>reodft11e-r2hc-odd.c</code> unless optimizations are disabled for that file.
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<p>
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<code>gcc</code> 2.95 on MacOS X miscompiles AltiVec code (fixed in
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later versions). <code>gcc</code> 3.2.x miscompiles AltiVec permutations, but FFTW has a workaround.
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<code>gcc</code> 4.0.1 on MacOS for Intel crashes when compiling FFTW; a workaround is to
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compile one file without optimization: <code>cd kernel; make CFLAGS=" " trig.lo</code>.
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<p>
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<code>gcc</code> 4.1.1 reportedly crashes when compiling FFTW for MIPS;
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the workaround is to compile the file it crashes on
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(<code>t2_64.c</code>) with a lower optimization level.
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<p>
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<code>gcc</code> versions 4.1.2 to 4.2.0 for x86 reportedly miscompile
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FFTW 3.1's test program, causing <code>make check</code> to crash (<code>gcc</code> bug #26528). The bug was reportedly fixed in
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<code>gcc</code> version 4.2.1 and later. A workaround is to compile
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<code>libbench2/verify-lib.c</code> without optimization.
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<h2><A name="solarisSucks">
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Question 2.4. FFTW does not compile on Solaris, complaining about
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<code>const</code>.
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</A></h2>
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We know that at least on Solaris 2.5.x with Sun's compilers 4.2 you
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might get error messages from <code>make</code> such as
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<p>
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<code>"./fftw.h", line 88: warning: const is a keyword in ANSI
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C</code>
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<p>
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This is the case when the <code>configure</code> script reports that <code>const</code> does not work:
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<p>
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<code>checking for working const... (cached) no</code>
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<p>
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You should be aware that Solaris comes with two compilers, namely,
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<code>/opt/SUNWspro/SC4.2/bin/cc</code> and <code>/usr/ucb/cc</code>. The latter compiler is non-ANSI. Indeed, it is a perverse shell script
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that calls the real compiler in non-ANSI mode. In order
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to compile FFTW, change your path so that the right
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<code>cc</code> is used.
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<p>
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To know whether your compiler is the right one, type
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<code>cc -V</code>. If the compiler prints ``<code>ucbcc</code>'', as in
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<p>
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<code>ucbcc: WorkShop Compilers 4.2 30 Oct 1996 C
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4.2</code>
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<p>
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then the compiler is wrong. The right message is something like
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<p>
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<code>cc: WorkShop Compilers 4.2 30 Oct 1996 C
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4.2</code>
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<h2><A name="3dnow">
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Question 2.5. What's the difference between
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<code>--enable-3dnow</code> and <code>--enable-k7</code>?
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</A></h2>
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<code>--enable-k7</code> enables 3DNow! instructions on K7 processors
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(AMD Athlon and its variants). K7 support is provided by assembly
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routines generated by a special purpose compiler.
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As of fftw-3.2, --enable-k7 is no longer supported.
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<p>
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<code>--enable-3dnow</code> enables generic 3DNow! support using <code>gcc</code> builtin functions. This works on earlier AMD
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processors, but it is not as fast as our special assembly routines.
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As of fftw-3.1, --enable-3dnow is no longer supported.
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<h2><A name="fma">
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Question 2.6. What's the difference between the fma and the non-fma
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versions?
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</A></h2>
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The fma version tries to exploit the fused multiply-add instructions
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implemented in many processors such as PowerPC, ia-64, and MIPS. The
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two FFTW packages are otherwise identical. In FFTW 3.1, the fma and
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non-fma versions were merged together into a single package, and the
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<code>configure</code> script attempts to automatically guess which
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version to use.
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<p>
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The FFTW 3.1 <code>configure</code> script enables fma by default on PowerPC, Itanium, and PA-RISC, and disables it otherwise. You can
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force one or the other by using the <code>--enable-fma</code> or <code>--disable-fma</code> flag for <code>configure</code>.
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<p>
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Definitely use fma if you have a PowerPC-based system with
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<code>gcc</code> (or IBM <code>xlc</code>). This includes all GNU/Linux systems for PowerPC and the older PowerPC-based MacOS systems. Also
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use it on PA-RISC and Itanium with the HP/UX compiler.
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<p>
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Definitely do not use the fma version if you have an ia-32 processor
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(Intel, AMD, MacOS on Intel, etcetera).
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<p>
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For other architectures/compilers, the situation is not so clear. For
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example, ia-64 has the fma instruction, but
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<code>gcc-3.2</code> appears not to exploit it correctly. Other compilers may do the right thing,
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but we have not tried them. Please send us your feedback so that we
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can update this FAQ entry.
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<h2><A name="languages">
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Question 2.7. Which language is FFTW written
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in?
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</A></h2>
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FFTW is written in ANSI C. Most of the code, however, was
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automatically generated by a program called
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<code>genfft</code>, written in the Objective Caml dialect of ML. You do not need to know ML or to
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have an Objective Caml compiler in order to use FFTW.
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<p>
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<code>genfft</code> is provided with the FFTW sources, which means that
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you can play with the code generator if you want. In this case, you
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need a working Objective Caml system. Objective Caml is available
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from <A href="http://caml.inria.fr">the Caml web page</A>.
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<h2><A name="fortran">
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Question 2.8. Can I call FFTW from Fortran?
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</A></h2>
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Yes, FFTW (versions 1.3 and higher) contains a Fortran-callable
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interface, documented in the FFTW manual.
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<p>
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By default, FFTW configures its Fortran interface to work with the
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first compiler it finds, e.g. <code>g77</code>. To configure for a different, incompatible Fortran compiler
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<code>foobar</code>, use <code>./configure F77=foobar</code> when installing FFTW. (In the case of <code>g77</code>, however, FFTW 3.x also includes an extra set of
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Fortran-callable routines with one less underscore at the end of
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identifiers, which should cover most other Fortran compilers on Linux
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at least.)
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<h2><A name="cplusplus">
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Question 2.9. Can I call FFTW from C++?
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</A></h2>
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Most definitely. FFTW should compile and/or link under any C++
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compiler. Moreover, it is likely that the C++
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<code><complex></code> template class is bit-compatible with FFTW's complex-number format
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(see the FFTW manual for more details).
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<h2><A name="whynotfortran">
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Question 2.10. Why isn't FFTW written in
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Fortran/C++?
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</A></h2>
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Because we don't like those languages, and neither approaches the
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portability of C.
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<h2><A name="singleprec">
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Question 2.11. How do I compile FFTW to run in single
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precision?
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</A></h2>
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On a Unix system: <code>configure --enable-float</code>. On a non-Unix system: edit <code>config.h</code> to <code>#define</code> the symbol <code>FFTW_SINGLE</code> (for FFTW 3.x). In both cases, you must then
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recompile FFTW. In FFTW 3, all FFTW identifiers will then begin with
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<code>fftwf_</code> instead of <code>fftw_</code>.
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<h2><A name="64bitk7">
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Question 2.12. --enable-k7 does not work on
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x86-64
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</A></h2>
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Support for --enable-k7 was discontinued in fftw-3.2.
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<p>
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The fftw-3.1 release supports --enable-k7. This option only works on
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32-bit x86 machines that implement 3DNow!, including the AMD Athlon
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and the AMD Opteron in 32-bit mode. --enable-k7 does not work on AMD
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Opteron in 64-bit mode. Use --enable-sse for x86-64 machines.
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<p>
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FFTW supports 3DNow! by means of assembly code generated by a
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special-purpose compiler. It is hard to produce assembly code that
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works in both 32-bit and 64-bit mode. <hr>
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Next: <a href="section3.html" rel=precedes>Using FFTW</a>.<br>
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Back: <a href="section1.html" rev=precedes>Introduction and General Information</a>.<br>
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<a href="index.html" rev=subdocument>Return to contents</a>.<p>
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<address>
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<A href="http://www.fftw.org">Matteo Frigo and Steven G. Johnson</A> / <A href="mailto:fftw@fftw.org">fftw@fftw.org</A>
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- 14 September 2021
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</address><br>
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Extracted from FFTW Frequently Asked Questions with Answers,
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Copyright © 2021 Matteo Frigo and Massachusetts Institute of Technology.
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</body></html>
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