Intel提供了丰富的浮点运算指令,
fcos
就是其中之一。下面就来实际试试看吧。
#include <stdio.h>
int main(int argc, char** argv) {
if(argc != 2) {
puts("usage: cos number");
return 1;
}
double f;
sscanf(argv[1], "%lf", &f);
printf("cos(%lf) = ", f);
__asm__ ("fldl (%0)\n\tfcos\n\tfstl (%0)" : : "r" (&f));
printf("%lf\n", f);
return 0;
}
编译运行,结果如下:
$ gcc cos.c -o cos
$ ./cos 1
cos(1.000000) = 0.540302
$ ./cos 3.1415926
cos(3.141593) = -1.000000
$ ./cos 0
cos(0.000000) = 1.000000
$ ./cos -3.1415926
cos(-3.141593) = -1.000000
$ ./cos 1.5707963
cos(1.570796) = 0.000000
$ ./cos -1.5707963
cos(-1.570796) = 0.000000
还是很方便的