Android NDK文档之 Android NDK CPU 功能侦测库

详细来自：http://blog.sina.com.cn/s/blog_4c451e0e0100sy90.html

Android NDK CPU Features detection library:

Android NDK CPU 功能侦测库：

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This NDK provides a small library named "cpufeatures" that canbe used at

runtime to detect the target device's CPU family and theoptional features

it supports.

NDK 提供一个小的名为 cpufeatures 的库，可以用来在运行时侦测目标设备的 CPU语系和它支持的可选功能。

Usage:

用法：

------

The library is available as an importmodule. 

该库是可作为导入模块使用的。

To use it, you must:

要使用它，你必须：

  * List 'cpufeatures' in your list of staticlibrary dependencies, as in:

  * 在你的静态库依赖列表中列出 cpufeatures ，如此：

       LOCAL_STATIC_LIBRARIES := cpufeatures

  * At the end of your Android.mk, import the'android/cpufeatures' module, as in:

  * 在你的 Android.mk 文件的末尾，导入android/cpufeatures 模块，如此：

       $(call import-module,android/cpufeatures)

  * In your source code, include the headernamed <cpu-features.h> , as in:

  * 在你的源代码中，包含名为 cpu-features.h的头文件，如此：

       #include<cpu-features.h>

Here is a simple example:

这里是一个简单示例：

<project-path>/jni/Android.mk:

    LOCAL_PATH := $(callmy-dir)

    include$(CLEAR_VARS)

    LOCAL_MODULE :=<your-module-name>

    LOCAL_SRC_FILES :=<your-source-files>

    LOCAL_STATIC_LIBRARIES:= cpufeatures

    include$(BUILD_SHARED_LIBRARY)

    $(callimport-module,android/cpufeatures)

Features:

功能：

---------

Two functions are provided for now:

现在提供了两个函数：

   AndroidCpuFamily  android_getCpuFamily();

Returns the target device's CPU Family as anenum. 

以枚举型式返回目标设备的 CPU 语系。

For now, the only supported family isANDROID_CPU_FAMILY_ARM.

现在，仅支持的语系是 ANDROID_CPU_FAMILY_ARM 。

   uint64_t  android_getCpuFeatures();

Returns the set of optional features supported by the device'sCPU.

返回设备 CPU 支持的可选功能集。

The result is a set of bit-flags, 

each corresponding to one CPU Family-specific optionalfeature.

结果是一组位标志，每一个对应一个 CPU 指定语系的可选功能。

Currently, only the following flags are defined, for the ARMCPU Family:

目前，只为 ARM CPU 语系定义了如下标志：

ANDROID_CPU_ARM_FEATURE_ARMv7

Indicates that the device's CPU supports the ARMv7-Ainstruction set 

as supported by the "armeabi-v7a" ABI (seeCPU-ARCH-ABIS.html).

指出设备的 CPU 支持 ARMv7-A 指令集与由 armeabi-v7a ABI 支持的等同(参见CPU-ARCH-ABIS.html)。

This corresponds to Thumb-2 and VFPv3-D16 instructions.

这相当于 Thumb-2 和 VFPv3-D16 指令。

ANDROID_CPU_ARM_FEATURE_VFPv3

Indicates that the device's CPU supports the VFPv3 hardwareFPU instruction set extension. 

指出设备的 CPU 支持 VFPv3 硬件浮点单元指令集扩展。

Due to the definition of 'armeabi-v7a',

this will always be the case if ANDROID_CPU_ARM_FEATURE_ARMv7is returned.

由于 armeabi-v7a 的定义，如果已返回 ANDROID_CPU_ARM_FEATURE_ARMv7这个将无例外地一起返回。

Note that this corresponds to the minimum profile VFPv3-D16that

_only_ provides 16 hardware FP registers.

注意相应的最小型 VFPv3-D16 仅支持 16 个硬件浮点寄存器。

详细来自：http://blog.sina.com.cn/s/blog_4c451e0e0100sy90.html
ANDROID_CPU_ARM_FEATURE_NEON

Indicates that the device's CPU supports the ARM AdvancedSIMD 

(a.k.a. NEON) vector instruction setextension. 

指出设备的 CPU 支持 ARM 高级的 SIMD (又叫做，NEON)矢量指令集扩展。

注：NEON 技术是用于多媒体处理的硬件加速。 

Note that ARM mandates that such CPUs also implementVFPv3-D32, 

which provides 32 hardware FP registers (shared with the NEONunit).

注意 ARM 要求这样的 CPU 同样实现 VFPv3-D32 提供 32 个硬件浮点寄存器(与 NEON单元共享)。

Important Note:

重要提示：

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The cpufeatures library will be updatedto 

support more CPU families and optional features in thefuture. 

在将来 cpufeatures 库将更新支持更多 CPU 语系和可选功能。

It is designed to work as-is on all official Android platformversions.

按现状它是被设计工作在全部官方 Android 平台版本上。

Change History:

修订记录：

---------------

Please see the comments in$NDK/sources/android/cpufeatures/cpu-features.c

for the complete change history for this library.

请参见 $NDK/sources/android/cpufeatures/cpu-features.c中的注释，了解这个库的完整修订记录。