compiling fftw3 in android ndk

hi i am new to android-ndk so far i worked with all sample applications in android-nd开发者_开发百科k,now i am trying to port fftw3 library in android, can you plz suggest me any tutorial for this.

Thanks.

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The FFTW3 build system makes use of Autotools, so that you can not use it directly with the Android NDK. A good blog post dealing with this issue is here.

The idea is to generate a proper config.h file offline and to create Android Makefiles, which replace the missing ones normally generated by the Autotools.

To achieve a modular layout for the different native modules you might use, I'd recommend the following:

In your top jni/ directory put these two files:

Application.mk:

    APP_OPTIM        := release
    APP_ABI          := armeabi armeabi-v7a
    APP_MODULES      := fftw3

Android.mk:

    TOP_DIR := $(call my-dir)
    include $(TOP_DIR)/fftw3/project/jni/Android.mk

This way you can easily add a new module by creating a jni/new_module_name directory and then adding new_module_name to the APP_MODULES list.

Then create a new jni/fftw3 directory and put another Application.mk there:

Application.mk:

    APP_PROJECT_PATH := $(call my-dir)/project
    APP_MODULES      += fftw3
    APP_OPTIM        := release
    APP_ABI          := armeabi armeabi-v7a

Then put the original FFTW3 package under jni/fftw3/project/jni.

At this point you need to generate a config.h. You can do this by using a small shell script like this.

The last step is to create the needed Android Makefile. In jni/fftw3/project/jni put a top Android.mk:

    LOCAL_PATH := $(call my-dir)
    include $(CLEAR_VARS)

    include $(LOCAL_PATH)/api/sources.mk
    include $(LOCAL_PATH)/dft/sources.mk
    include $(LOCAL_PATH)/dft/scalar/sources.mk
    include $(LOCAL_PATH)/dft/scalar/codelets/sources.mk
    include $(LOCAL_PATH)/kernel/sources.mk
    include $(LOCAL_PATH)/rdft/sources.mk
    include $(LOCAL_PATH)/rdft/scalar/sources.mk
    include $(LOCAL_PATH)/rdft/scalar/r2cb/sources.mk
    include $(LOCAL_PATH)/rdft/scalar/r2cf/sources.mk
    include $(LOCAL_PATH)/rdft/scalar/r2r/sources.mk
    include $(LOCAL_PATH)/reodft/sources.mk

    LOCAL_MODULE := fftw3
    LOCAL_C_INCLUDES := $(LOCAL_PATH) \
        $(LOCAL_PATH)/api \
        $(LOCAL_PATH)/dft \
        $(LOCAL_PATH)/dft/scalar \
        $(LOCAL_PATH)/dft/scalar/codelets \
        $(LOCAL_PATH)/kernel \
        $(LOCAL_PATH)/rdft \
        $(LOCAL_PATH)/rdft/scalar \
        $(LOCAL_PATH)/rdft/scalar/r2cb \
        $(LOCAL_PATH)/rdft/scalar/r2cf \
        $(LOCAL_PATH)/rdft/scalar/r2r \
        $(LOCAL_PATH)/reodft

    # Use APP_OPTIM in Application.mk
    LOCAL_CFLAGS := -g

    include $(BUILD_SHARED_LIBRARY)

Frow now on you have to create all these sources.mk files. E.g. a typical sources.mk looks like this:

rdft/sources.mk:

    sources = buffered2.c \
              buffered.c \
              <....>
              vrank-geq1.c \
              vrank-geq1-rdft2.c

    LOCAL_SRC_FILES += $(sources:%=rdft/%)

Call the ndk-build script in the top directory of your app and you should end up with two ready-to-use FFTW3 libraries:

• libs/armeabi-v7a/libfftw3.so
• libs/armeabi/libfftw3.so

---

I currently solving similar problem, but without significant results.

As I can recommend use anther well tested library like JTransforms (java pretty fast) or find Badlogic KissFFT implementation (JNI, about 2 times faster, numerical unstable).

---

After noticing, that there's a ton of new directories in recent fftw version, containing .c and not listed in the original Android.mk, I got too lazy to write source.mk-generating script, and googled this instead:

include $(LOCAL_PATH)/api/sources.mk

Thanks to Sudhakar Fomra (sfomra at github), got my build done in few minutes.

https://github.com/sfomra/FFTW3_MOD-for-Android

---

The best way to compile fftw3 for Android armeabi-v7a is:

export SYSROOT="$NDK_ROOT/platforms/$TARGET/arch-arm"
export CFLAGS="-I$NDK_ROOT/platforms/$TARGET/arch-arm/usr/include --sysroot=$SYSROOT"
export CPPFLAGS="-I$NDK_ROOT/platforms/$TARGET/arch-arm/usr/include --sysroot=$SYSROOT"
export CC=$($NDK_ROOT/ndk-which gcc)
export LD=$($NDK_ROOT/ndk-which ld)
export CPP=$($NDK_ROOT/ndk-which cpp)
export CXX=$($NDK_ROOT/ndk-which g++)
export AS=$($NDK_ROOT/ndk-which as)
export AR=$($NDK_ROOT/ndk-which ar)
export RANLIB=$($NDK_ROOT/ndk-which ranlib)
./configure --host=arm-linux-androideabi --target=arm-linux-androideabi
make OS=android NDKROOT=$NDK_ROOT TARGET=android-9 ARCH=arm NDKLEVEL=9

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Quite painlessly, FFTW can be built for Android with its official CMake script in http://fftw.org/fftw-3.3.8.tar.gz:

externalNativeBuild {
    cmake {
        arguments "-DANDROID_ARM_NEON=TRUE"
        arguments "-DCMAKE_BUILD_TYPE=Release"
        arguments "-DBUILD_SHARED_LIBS=OFF"
        arguments "-DBUILD_TESTS=OFF"
        arguments "-DDISABLE_FORTRAN=ON"
        arguments "-DENABLE_FLOAT=ON"
        targets "fftw3f"
    }
}