NDK Programmer's Guide
CPU Features

This NDK provides a small library named "`cpufeatures`" that can be used at runtime to detect the target device's CPU family and the optional features it supports.

Usage

The library is available as an import module. To use it, you must:

  • List 'cpufeatures' in your list of static library dependencies, as in:
    LOCAL_STATIC_LIBRARIES := cpufeatures
    
  • At the end of your Android.mk, import the 'android/cpufeatures' module, as in:
    $(call import-module,android/cpufeatures)
    
  • In your source code, include the header named <cpu-features.h>

Here is a simple example:

    <project-path>/jni/Android.mk:
        LOCAL_PATH := $(call my-dir)

        include $(CLEAR_VARS)
        LOCAL_MODULE := <your-module-name>
        LOCAL_SRC_FILES := <your-source-files>
        LOCAL_STATIC_LIBRARIES := cpufeatures
        include $(BUILD_SHARED_LIBRARY)

        $(call import-module,android/cpufeatures)

Features

Two functions are provided for now:

    AndroidCpuFamily android_getCpuFamily();

Returns a value matching the CPU family/architecture supported by the current process as an enum. Currently, the following families are defined:

  • ANDROID_CPU_FAMILY_ARM
  • ANDROID_CPU_FAMILY_X86
  • ANDROID_CPU_FAMILY_MIPS
  • ANDROID_CPU_FAMILY_ARM64
  • ANDROID_CPU_FAMILY_X86_64
  • ANDROID_CPU_FAMILY_MIPS64

Note that when running a 32-bit executable on a 64-bit system, this function will return the 32-bit family value only.

Secondly:

    uint64_t android_getCpuFeatures();

Returns the set of optional features supported by the device's CPU. The result is a set of bit-flags, each corresponding to one CPU Family-specific optional feature.

Currently, only the following flags are defined, for the 32-bit ARM CPU Family:

  • ANDROID_CPU_ARM_FEATURE_VFPv2
    Indicates that the device's CPU supports VFPv2 instruction set. Most ARMv6 CPUs support these.
  • ANDROID_CPU_ARM_FEATURE_ARMv7
    Indicates that the device's CPU supports the ARMv7-A instruction set as supported by the "armeabi-v7a" abi (see CPU-ARCH-ABIS.html). This corresponds to Thumb-2 and VFPv3-D16 instructions.
  • ANDROID_CPU_ARM_FEATURE_VFPv3
    Indicates that the device's CPU supports the VFPv3 hardware FPU instruction set extension. Due to the definition of 'armeabi-v7a', this will always be the case if ANDROID_CPU_ARM_FEATURE_ARMv7 is returned.

    Note that this corresponds to the minimum profile VFPv3-D16 that only provides 16 hardware double-precision FP registers.

  • ANDROID_CPU_ARM_FEATURE_VFP_D32
    Indicates that the device's CPU supports 32 hardware double-precision FP registers instead of 16. Note that there are still only 32 single- precision registers mapped to the same register banks.
  • ANDROID_CPU_ARM_FEATURE_NEON
    Indicates that the device's CPU supports the ARM Advanced SIMD (a.k.a. NEON) vector instruction set extension. Note that ARM mandates that such CPUs also implement VFPv3-D32, which provides 32 hardware FP registers (shared with the NEON unit).
  • ANDROID_CPU_ARM_FEATURE_VFP_FP16
    Indicates that the device's CPU supports instructions to perform floating-point operations on 16-bit registers. This is part of the VFPv4 specification.
  • ANDROID_CPU_ARM_FEATURE_VFP_FMA
    Indicates that the device's CPU supports fused multiply-accumulate VFP instructions extension. Also part of the VFPv4 specification.
  • ANDROID_CPU_ARM_FEATURE_NEON_FMA
    Indicates that the device's CPU supports fused multiply-accumulate NEON instructions extension. Also part of the VFPv4 specification.
  • ANDROID_CPU_ARM_FEATURE_IDIV_ARM
    Indicates that the device's CPU supports Integer division in ARM mode. Only available on recent CPUs (e.g. Cortex-A15).
  • ANDROID_CPU_ARM_FEATURE_IDIV_THUMB2
    Indicates that the device's CPU supports Integer division in Thumb-2 mode. Only available on recent CPUs (e.g. Cortex-A15).
  • ANDROID_CPU_ARM_FEATURE_iWMMXt
    Indicates that the device's CPU supports extension that adds MMX registers and instructions. This is only available on a few XScale- based CPU.
  • ANDROID_CPU_ARM_FEATURE_LDREX_STREX
    Indicates that the device's CPU supports LDREX and STREX instructions available since ARMv6. Together they provide atomic update on memory with the help of exclusive monitor.

And the following flags for the 32-bit x86 CPU Family:

  • ANDROID_CPU_X86_FEATURE_SSSE3
    Indicates that the device's CPU supports the SSSE3 instruction extension set. Note that this is unlike SSE3 which is required by the x86 NDK ABI.
  • ANDROID_CPU_X86_FEATURE_POPCNT
    Indicates that the device's CPU supports the POPCNT instruction.
  • ANDROID_CPU_X86_FEATURE_MOVBE
    Indicates that the device's CPU supports the MOVBE instruction. This one is specific to some Intel IA-32 CPUs, like the Atom.

And the following flags for the 64-bit ARM CPU Family:

  • ANDROID_CPU_ARM64_FEATURE_FP
    Indicates that the device's CPU has Floating Point (FP) unit. All Android ARM64 devices are required to support this feature.
  • ANDROID_CPU_ARM64_FEATURE_ASIMD
    Indicates that the device's CPU has Advanced SIMD (ASIMD) unit. All Android ARM64 devices are required to support this feature.
  • ANDROID_CPU_ARM64_FEATURE_AES
    Indicates that the device's CPU supports AES instructions.
  • ANDROID_CPU_ARM64_FEATURE_CRC32
    Indicates that the device's CPU supports CRC32 instructions.
  • ANDROID_CPU_ARM64_FEATURE_SHA1
    Indicates that the device's CPU supports SHA1 instructions.
  • ANDROID_CPU_ARM64_FEATURE_SHA2
    Indicates that the device's CPU supports SHA2 instructions.
  • ANDROID_CPU_ARM64_FEATURE_PMULL
    Indicates that the device's CPU supports 64-bit PMULL and PMULL2 instructions.

Other CPU families do not have extensions listed at the moment, which means that android_getCpuFeatures() will return 0 for them.

The following function is also defined to return the max number of CPU cores on the target device:

    int  android_getCpuCount(void);

Important Note

The cpufeatures library will be updated to support more CPU families and optional features in the future. It is designed to work as-is on all official Android platform versions.

Change History

Please see the comments in $NDK/sources/android/cpufeatures/cpu-features.c for the complete change history for this library.