【翻译】(9)CPU Features

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介绍了Android NDK提供的cpufeatures库，该库可用于运行时检测目标设备的CPU家族及支持的特性。支持ARM家族，并提供了检测ARMv7指令集、VFPv3 FPU扩展及NEON向量指令集的功能。

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英文文档见android-ndk-r5b的documentation.html

属于Android Native Development Kit (NDK)的一部分

见http://developer.android.com/sdk/ndk/（需要代理）

翻译仅个人见解

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Android NDK CPU Features detection library:

Android NDK CPU特性检测库：

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

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.

NDK提供一个名为cpufeatures的小型库，它可以用于在运行期检测目标设备的CPU家族和它支持的可选特性。

Usage:

用法：

------

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

这个库作为导入模块可用。要使用它，你必须：

To use it, you must:

要使用它，你必须：

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

* 在你的静态库依赖列表中列出cpufeatures，正如这样：

LOCAL_STATIC_LIBRARIES := cpufeatures

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

* 在你的Android.mk结束处，导入android/cpufeatures模块，正如这样：

$(call import-module,android/cpufeatures)

* In your source code, include the header named <cpu-features.h>

* 在你的源代码中，包含名为<cpu-features.h>的头文件

Here is a simple example:

这里是一个简单示例：

<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:

特性：

---------

Two functions are provided for now:

现在提供两个函数：

AndroidCpuFamily android_getCpuFamily();

Returns the target device's CPU Family as an enum. For now, the only supported family is ANDROID_CPU_FAMILY_ARM.

用一个枚举值返回目标设备的CPU家族。现在，唯一支持的家族是ANDROID_CPU_FAMILY_ARM。

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.

返回设备CPU支持的可选特性。结构是一个位标志集合，每个位标志对应一项CPU家族特定的可选特性。

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

目前，只为ARM CPU家族定义了如下标志：

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_ARMv7

指出设备的CPU支持ARMv7-A指令集，它由armeabi-v7a的ABI（注：应用程序二进制接口，操作系统暴露的接口，使二进制程序不需要重新编译即可在兼容ABI的操作系统上运行）支持（参考CPU-ARCH-ABIS.html）。它对应Thumb-2和VFPv3-D16指令。

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.

ANDROID_CPU_ARM_FEATURE_VFPv3

指出设备CPU支持VFPv3硬件FPU（注：FPU是浮点运算单元的缩写）指令集扩展。由于armeabi-v7a的定义，它将总是返回ANDROID_CPU_ARM_FEATURE_ARMv7（注：这里的意思可能是，它总是和ANDROID_CPU_ARM_FEATURE_ARMv7一起返回）。

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

注意它对应最小型号是VFPv3-D16，它只提供16个硬件浮点寄存器。

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_NEON

指出设备CPU支持ARM高级SIMD（即NEON）（注：NEON技术是ARM SIMD扩展指令，用于多媒体处理的硬件加速）向量指令集扩展。注意ARM授权这种CPU还实现了VFPv3-D32，提供32个硬件浮点寄存器（与NEON单元共享）。

Important Note:

重要注意事项：

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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.

cpufeatures库将被更新以支持未来更多CPU家族和可选特性。它被设计为在所有官方Android平台版本上保持原样地工作。

Change History:

修改历史：

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

请参考$NDK/sources/android/cpufeatures/cpu-features.c中的注释以获得这个库的完整修改历史。（注：估计写文档的人太懒...）