ngspice/visualc/how-to-fftw.txt

../../fftw-3.3-dll32 and ../../fftw-3.3-dll64
are the places to deploy the appropriate 32/64 bit version
of the fftw3 libraries under VC++ which can be found here:

 http://www.fftw.org/install/windows.html

More precisely (here in case of the 32 bit version 3.3.5),
 - you have to create the directory ../../fftw-3.3-dll32
    (which is side by side and thus outside of the ngspice source tree)
 - you have to fetch fftw-3.3.5-dll32.zip and deploy it there
 - you have to unpack this .zip there

At least you need to unpack these three files
  fftw3.h
  libfftw3-3.dll
  libfftw3-3.def

Then use vngspice-fftw.vcxproj to compile ngspice

If you need to distribute ngspice.exe to another directory,
copy the appropriate libfftw3-3.dll into the same directory or 
to a place which is in your PATH environment.

----

(compile
  "url=ftp://ftp.fftw.org/pub/fftw
       for i in fftw-3.3-dll32 fftw-3.3-dll64 ; do
           dst=../../$i
           mkdir -p $dst
           (cd $dst && wget $url/$i.zip && unzip $i.zip)
       done")