Enable Neon Intrinsics support in Android Studio

Before you begin

You will need a x86_64 or Apple M1 computer with Android Studio installed. Currently, Android Studio is not supported on Windows and Linux machines with Arm based CPUs.

You will also need a Armv8 powered smartphone running Android to run your application on. We tested the application in this learning path on a Google Pixel 7 smartphone.

Overview

Do not repeat yourself (DRY) is one of the major principles of software development. Following this principle means reusing your code using functions. However, invoking a function adds extra overhead. In certain cases compilers can reduce this overhead by taking advantage of built-in functions called intrinsics. The compiler replaces the intrinsics that are used in high-level programming languages, for example C/C++, with mostly 1:1 mapped assembly instructions.

To further improve performance, you need to use assembly code. However, with Arm Neon intrinsics you can avoid the complication of writing assembly functions. Instead you only need to program in C/C++ and call the intrinsics or instruction functions that are declared in the arm_neon.h header file. Neon intrinsics can improve the performance of your application.

Arm Neon intrinsics technology is an advanced Single Instruction Multiple Data (SIMD) architecture extension for Arm processors. SIMD performs the same operation on a sequence, or vector, of data during a single CPU cycle.

Enable Neon Intrinsics support in Android Studio

In this section, you will setup your Android development environment to use Neon instrinsics.

1. Open Android Studio on your development machine.

2. Create a project using the Native C++ Project option in the Phone and Tablet section and click Next, as shown below:

3. Set the application name to Neon Intrinsics, select Java as the language, leave the Minimum SDK selection as API 24: Android 7.0(Nougat) and click Next, as shown below:

4. Leave the Toolchain Default selection for C++ Standard and then click Finish, as shown below:

5. Install CMake and Android NDK. Click on File->Settings. On the left pane, under System Settings select Android SDK. From the tabs on the right, click on SDK Tools. Select the CMake and NDK(Side by side) packages and click on Apply followed by OK, as shown below:

6. The project that you created comprises of one activity that is implemented within the MainActivity class. It prints a “Hello from C++” string in the app which comes from the native-lib library. Open app/cpp/native-lib.cpp as shown below to view the code for this library:

7. The Android NDK supports different Application Binary Interfaces(ABI). Set the NDK for this project to use arm64-v8a ABI. This ABI is for Armv8-A based CPUs, which support the 64-bit Arm architecture. On the left pane, expand Gradle Scripts and open build.gradle(Module :app) file. Add the line below to the defaultConfig section:

    

        
        
            ndk.abiFilters 'arm64-v8a'
        
    

The code in this section should look like:

    

        
        
            defaultConfig {
        applicationId "com.example.neonintrinsics"
        minSdk 24
        targetSdk 33
        versionCode 1
        versionName "1.0"
        ndk.abiFilters 'arm64-v8a'

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
        
    

8. Enable support for Neon intrinsics, by passing the following CMake argument in build.grade(Module :app)

    

        
        
            arguments "-DANDROID_ARM_NEON=ON" 
        
    

This argument is added under externalNativeBuild in the defaultConfig section of the file. The complete build.gradle(Module :app) file is shown below for completeness:

    

        
        
            plugins {
    id 'com.android.application'
}

android {
    namespace 'com.example.neonintrinsics'
    compileSdk 33

    defaultConfig {
        applicationId "com.example.neonintrinsics"
        minSdk 24
        targetSdk 33
        versionCode 1
        versionName "1.0"
        ndk.abiFilters 'arm64-v8a'
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake{
                arguments "-DANDROID_ARM_NEON=ON"
            }
        }

    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    externalNativeBuild {
        cmake {
            path file('src/main/cpp/CMakeLists.txt')
            version '3.22.1'
        }
    }
    buildFeatures {
        viewBinding true
    }
}

dependencies {

    implementation 'androidx.appcompat:appcompat:1.6.1'
    implementation 'com.google.android.material:material:1.9.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.4'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.5'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.1'
}
        
    

With these changes you can use Neon intrinsics, which are declared within the arm_neon.h header.

9. Build the application to make sure your Android app development setup is working properly. Select Build->Make Project. When the build completes, you should see messages in the Build console similar to those shown below:

    

        
        BUILD SUCCESSFUL in 2m 44s
37 actionable tasks: 37 executed

Build Analyzer results available

        
    

10. Run this application on an 64-bit Arm powered smartphone running Android. We ran the app on a Google Pixel 7 phone using a USB cable connected to the development machine running Android Studio. You can also pair your phone over Wi-Fi.
    Connect your device and select Tools->Device Manager. Select the Physical tab and your connected phone should show up on the list of devices as shown in the image below:

Then select Run->Run app or press Shift+F10 to run the app on the connected phone.

The output from the app running on the Google Pixel 7 running Android 13 is shown below:

You have now successfully setup and validated your Android development environment for running applications with Neon intrinsics on a 64-bit Arm powered smartphone.

In the next section, you will implement the dot product of two vectors using Neon intrinsics.