anchor.diff:      sha256 = "0g8qk98lgq770ixdf7n36yd5xjsgm2v3wzvnphwmhy6r4y2amx0y";
     };
   
  -  outputs = [ "out" "dev" "man" "info" ]; # it's dev-doc only
  +  outputs = [ "out" "dev" "man" ]
  +    ++ optional withDoc "info"; # it's dev-doc only
     outputBin = "dev"; # fftw-wisdom
   
     configureFlags =
  
positive.code: 
  assert elem precision [ "single" "double" "long-double" "quad-precision" ];
  
  let version = "3.3.6-pl1"; in
  
  stdenv.mkDerivation rec {
    name = "fftw-${precision}-${version}";
  
negative.code:     ++ optional (stdenv.isx86_64 && (precision == "single" || precision == "double") )  "--enable-sse2"
      ++ optional stdenv.cc.isGNU "--enable-openmp"
      # doc generation causes Fortran wrapper generation which hard-codes gcc
      ++ optional (!withDoc) "--disable-doc";
  
    enableParallelBuilding = true;
  
  