在GCC师SIMD（SSE）指令 [英] SIMD (SSE) instruction for division in GCC

问题描述

我想用最优化的SSE指令下面的代码片断如果可能的话：

I'd like to optimize the following snippet using SSE instructions if possible:

/*
 * the data structure
 */
typedef struct v3d v3d;
struct v3d {
    double x;
    double y;
    double z;
} tmp = { 1.0, 2.0, 3.0 };

/*
 * the part that should be "optimized"
 */
tmp.x /= 4.0;
tmp.y /= 4.0;
tmp.z /= 4.0;

这是可能的呢？

推荐答案

您正在寻找的内在是 _mm_div_pd 。这里是一个工作的例子应该是足够引导你在正确的方向：

The intrinsic you are looking for is _mm_div_pd. Here is a working example which should be enough to steer you in the right direction:

#include <stdio.h>

#include <emmintrin.h>

typedef struct
{
    double x;
    double y;
    double z;
} v3d;

typedef union __attribute__ ((aligned(16)))
{
    v3d a;
    __m128d v[2];
} u3d;

int main(void)
{
    const __m128d vd = _mm_set1_pd(4.0);
    u3d u = { { 1.0, 2.0, 3.0 } };

    printf("v (before) = { %g %g %g }\n", u.a.x, u.a.y, u.a.z);

    u.v[0] = _mm_div_pd(u.v[0], vd);
    u.v[1] = _mm_div_pd(u.v[1], vd);

    printf("v (after) = { %g %g %g }\n", u.a.x, u.a.y, u.a.z);

    return 0;
}

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