---
title: 内嵌汇编实现示例
description: "C语言实现版本："
url: https://www.hikunpeng.com/document/detail/zh/perftuning/progtuneg/kunpengprogramming_05_0023.html
sourcePath: /source/zh/perftuning/progtuneg/kunpengprogramming_05_0023.html
indexId: 3e22067a1249663f330162da3936cac770b9cd41588e4f9ff519e1b4e9d76ac163
---
# 内嵌汇编实现示例

C语言实现版本：

```
void AddFloatC(float* dst, float* src1, float* src2, int count)
{
for (int i = 0; i < count; i++) {
dst[i] = src1[i] + src2[i];
}
}
int main()
{
float dst[ARRAY_NUMS] = {0.0};
float src1[ARRAY_NUMS];
float src2[ARRAY_NUMS];
struct timeval start;
struct timeval end;
double dt;
InitArray(dst, src1, src2);
gettimeofday(&start,NULL);
AddFloatNeonAsm(dst, src1, src2, ARRAY_NUMS);
gettimeofday(&end,NULL);
dt=(end.tv_sec-start.tv_sec) * 1000+(end.tv_usec-start.tv_usec) / 1000.0;
cout<<"Time used of Normal NEON ASM code: "<<dt<<"ms"<<"\tcheck dst[52] value: "<<dst[52]<<endl;
return 0;
}
```

内嵌汇编实现版本：

```
void AddFloatNeonAsm(float* dst, float* src1, float* src2, int count)
{
__asm__ volatile(
"1:                               \n"
"ld1     {v0.4s}, [%[src1]], #16  \n"
"ld1     {v1.4s}, [%[src2]], #16  \n"
"fadd    v0.4s, v0.4s, v1.4s      \n"
"subs    %[count], %[count], #4   \n"
"st1     {v0.4s}, [%[dst]], #16   \n"
"bgt     1b                       \n"
: [dst] "+r" (dst)
: [src1] "r" (src1), [src2] "r" (src2), [count] "r" (count)
: "memory", "v0", "v1"
);
}
int main()
{
float dst[ARRAY_NUMS] = {0.0};
float src1[ARRAY_NUMS];
float src2[ARRAY_NUMS];
struct timeval start;
struct timeval end;
double dt;
InitArray(dst, src1, src2);
gettimeofday(&start,NULL);
AddFloatC(dst, src1, src2, ARRAY_NUMS);
gettimeofday(&end,NULL);
dt=(end.tv_sec-start.tv_sec) * 1000 + (end.tv_usec-start.tv_usec) / 1000.0;
cout<<"Time used of Normal C code: "<<dt<<"ms"<<"\t\tcheck dst[52] value: "<<dst[52]<<endl;
return 0;
}
```

其中的bgt跳转指令会去读取NZCV系统寄存器中相应的NZCV标记位以判断是否满足跳转条件，关键在于subs指令不同于普通的sub指令，在做减法时，会对相应condition flags位进行操作。

“bgt 1b”中的b的含义是：避免bgt把后面的1当成立即数处理，所以在1后加了b，告知编译器前面的1表示label，而不是立即数。

C语言执行时间为3.062ms，而NEON内嵌汇编的版本执行时间为0.331ms。