C/C++使用__builtin_sqrt与__builtin_sqrtf。
这两个属于内置函数,使用硬件加速运算。
The __builtin_sqrt() and __builtin_sqrtf() functions are supported only when hardware floating point support is enabled. In addition, the __builtin_sqrt() function is not supported if --float_support is set to fpv4spd16.
意思是这两个函数需要硬件启用了浮点支持。
(来源:http://downloads.ti.com/docs/esd/SPNU151/built-in-functions-stdz0554909.html)
速度对比:
对1e8个数字进行根号运算。
普通sqrt:
#include <bits/stdc++.h>
using namespace std;
int main()
{
for (int i = 1; i <= 100000000; i++)
double num = sqrt(1.0 * i);
cout << clock() << "ms" << endl;
return 0;
}
__builtin_sqrt:
#include <bits/stdc++.h>
using namespace std;
int main()
{
for (int i = 1; i <= 100000000; i++)
double num = __builtin_sqrt(1.0 * i);
cout << clock() << "ms" << endl;
return 0;
}
__builtin_sqrtf:
#include <bits/stdc++.h>
using namespace std;
int main()
{
for (int i = 1; i <= 100000000; i++)
double num = __builtin_sqrtf(1.0 * i);
cout << clock() << "ms" << endl;
return 0;
}
两者都较普通sqrt快了近十倍。
__builtin_sqrt与__builtin_sqrtf的区别:
#include <bits/stdc++.h>
using namespace std;
int main()
{
cout << sizeof (__builtin_sqrt(9)) << endl;
cout << sizeof (__builtin_sqrtf(9)) << endl;
return 0;
}
一个返回8个字节的double型,另一个则返回4个字节的float型。