arm neon 函数详解

前面一篇博客有介绍arm_neon.h中函数的定义，以及大致的功能和作用，为了进一步加深对这些函数的理解，我们通过运行代码来验证。

在android studio中创建一个android工程，然后在jni代码中调用arm_neon.h中的函数

为了方便大家学习，我上传了一个demo，ARMNeonDemo

下载解压后，导入android studio就可以了。

打开上面native.cpp这个文件,在如下函数中添加demo code就可以了，例如

static void neon(JNIEnv *env) {
    LOGD("the function for test neon start.");
    int8_t s8[]={1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31};
    int8x16_t a=vld1q_s8(s8);  //赋值，a=1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16
    int8x16_t b=vld1q_s8(s8);  //赋值，b=1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16
    //int8x16_t   vaddq_s8(int8x16_t a, int8x16_t b); // VADD.I8 q0,q0,q0
    int8x16_t c=vaddq_s8(a,b); //add 后面的q表示正常指令，c应该是2,4,6,8,10 ...
    int8_t ret[16]={0};
    vst1q_s8(ret,c);   //把c的值赋给ret数组，这样是为了方便打印，验证结果
    for(int i=0;i<16;i++){
        LOGD("ret[%d] is %d ",i,ret[i]);
    }
    LOGD("the function for test neon end.");
}

编译运行后的结果如下

08-18 14:52:24.722 14304-14304/com.hxiong.neondemo I/neon_demo_jni: JNI_OnLoad
08-18 14:52:24.723 14304-14304/com.hxiong.neondemo D/neon_demo_jni: the function for test neon start.
08-18 14:52:24.723 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[0] is 2 
08-18 14:52:24.723 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[1] is 4 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[2] is 6 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[3] is 8 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[4] is 10 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[5] is 12 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[6] is 14 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[7] is 16 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[8] is 18 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[9] is 20 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[10] is 22 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[11] is 24 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[12] is 26 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[13] is 28 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[14] is 30 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: ret[15] is 32 
08-18 14:52:24.724 14304-14304/com.hxiong.neondemo D/neon_demo_jni: the function for test neon end.