ARM neon 指令 （Android）代码环境配置

本次使用的ARM平台是手机平台

1. 首先确保安装好了NDK
   配置好了PATH变量，将NDK路径加入PATH
2. CMakeList 设置

   cmake_minimum_required (VERSION 3.16)
   project (Dome)
   add_subdirectory(./src/neon)
   add_executable(neon neon.cpp)
   set_target_properties(neon PROPERTIES RUNTIME_OUTPUT_DIRECTORY "${CMAKE_SOURCE_DIR}/build")
   
   target_link_libraries(neon PRIVATE c++_static dl)
   
   set(THIS_COMPILE_FLAGS -march=armv8-a)
   
   target_compile_options(neon PRIVATE ${THIS_COMPILE_FLAGS})

3. 编译脚本

   cmake .. \
   -DCMAKE_TOOLCHAIN_FILE=$ANDROID_NDK/build/cmake/android.toolchain.cmake \
   -DCMAKE_BUILD_TYPE=Debug \
   -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \
   -DANDROID_ABI="arm64-v8a" \
   -DANDROID_STL=c++_static \
   -DANDROID_NATIVE_API_LEVEL=android-21  \
   -DMNN_BUILD_FOR_ANDROID_COMMAND=true \
   -DANDROID_TOOLCHAIN=clang \
   -DCMAKE_GENERATOR="Unix Makefiles"

4. 运行

   adb push neon  /data/local/tmp && adb shell /data/local/tmp/neon

5. 源代码

   #include <stdio.h>
   #include <stdlib.h>
   #include <arm_neon.h>
   #include <math.h>
   #include <cstddef>
   
   int main()
   {
       //定义a, b, c
       unsigned char a[8] = {0, 1, 2, 3, 4, 5, 6, 7};
       unsigned char b[8] = {8, 9, 10, 11, 12, 13, 14, 15};
       unsigned char c[8];
       uint8x8_t rega, regb, regc;	//定义3个8x8bit无符号整型的 NEON 寄存器
       //加载 a, b 到寄存器
       rega = vld1_u8(&a[0]);
       regb = vld1_u8(&b[0]);
       regc = vadd_u8(rega, regb);	//做加法
       vst1_u8(&c[0], regc);		//回写到c中
       //测试
       for(int i = 0 ; i < 8 ; i++)
       {
           printf("%d 	",c[i] );
       }
       printf("\n");
   }