c++ SSE2的内在特性

我刚刚了解到有一种方法可以使用intrinsic实现一些并行化。我发现下面的代码，并想通过它，但我可以理解很多。我试图使运算达到单精度，但我怎么能做到呢?

#include <stdio.h>
#include <stdlib.h>
#include <xmmintrin.h>
inline double pi_4 (int n){
        int i;
        __m128d mypart2,x2, b, c, one;
        double *x = (double *)malloc(n*sizeof(double));
        double *mypart = (double *)malloc(n*sizeof(double));
        double sum = 0.0;
        double dx = 1.0/n;
        double x1[2] __attribute__((aligned(16)));
        one = _mm_set_pd1(1.0); // set one to (1,1)
        for (i = 0; i < n; i++){
                x[i] = dx/2 + dx*i;
        }
        for (i = 0; i < n; i+=2){
                x1[0]=x[i]; x1[1]=x[i+1];
                x2 = _mm_load_pd(x1);
                b = _mm_mul_pd(x2,x2);
                c = _mm_add_pd(b,one);
                mypart2 = _mm_div_pd(one,c); 
                _mm_store_pd(&mypart[i], mypart2);
        }
        for (i = 0; i < n; i++)
                sum += mypart[i];       
        return sum*dx;
}
int main(){
        double res;
        res=pi_4(128);
        printf("pi = %lfn", 4*res);
        return 0;
}

我正在考虑将一切从double改为float，并调用正确的内在函数，例如，而不是_mm_set_pd1 -> _mm_set_ps1。我不知道这是否会使程序从双精度变成单精度。

我尝试如下，但我得到一个分割错误

#include <stdio.h>
#include <stdlib.h>
#include <xmmintrin.h>
inline float pi_4 (int n){
        int i;
        __m128 mypart2,x2, b, c, one;
        float *x = (float *)malloc(n*sizeof(float));
        float *mypart = (float*)malloc(n*sizeof(float));
        float sum = 0.0;
        float dx = 1.0/n;
        float x1[2] __attribute__((aligned(16)));
        one = _mm_set_ps1(1.0); // set one to (1,1)
        for (i = 0; i < n; i++){
                x[i] = dx/2 + dx*i;
        }
        for (i = 0; i < n; i+=2){
                x1[0]=x[i]; x1[1]=x[i+1];
                x2 = _mm_load_ps(x1);
                b = _mm_mul_ps(x2,x2);
                c = _mm_add_ps(b,one);
                mypart2 = _mm_div_ps(one,c); 
                _mm_store_ps(&mypart[i], mypart2);
        }
        for (i = 0; i < n; i++)
                sum += mypart[i];       
        return sum*dx;
}
int main(){
        float res;
        res=pi_4(128);
        printf("pi = %lfn", 4*res);
        return 0;
}