SSE版本的结果不同

我正在尝试重写一些代码以利用SSE。然而，由于某种原因，我的SSE版本产生了与原始版本不同的结果，例如209.1而不是1.47等

为什么？整个函数可以在这里找到。

struct vec_ps
{
    __m128 value;
    vec_ps(){}  
    vec_ps(float value)         : value(_mm_set1_ps(value)) {}
    vec_ps(__m128 value)        : value(value)              {}
    vec_ps(const vec_ps& other) : value(other.value)        {}
    vec_ps& operator=(const vec_ps& other)
    {
        value = other.value;
        return *this;
    }
    vec_ps& operator+=(const vec_ps& other)
    {
        value = _mm_add_ps(value, other.value);
        return *this;
    }
    vec_ps& operator-=(const vec_ps& other)
    {
        value = _mm_sub_ps(value, other.value);
        return *this;
    }
    vec_ps& operator*=(const vec_ps& other)
    {
        value = _mm_mul_ps(value, other.value);
        return *this;
    }
    vec_ps& operator/=(const vec_ps& other)
    {
        value = _mm_div_ps(value, other.value);
        return *this;
    }
    static vec_ps load(float* ptr)
    {
        return vec_ps(_mm_load_ps(ptr));
    }
    static void stream(float* ptr, const vec_ps& other)
    {
        _mm_stream_ps(ptr, other.value);
    }
    void stream(float* ptr)
    {
        _mm_stream_ps(ptr, value);
    }
};
vec_ps operator+(const vec_ps& lhs, const vec_ps& rhs)
{       
    return vec_ps(lhs) += rhs;
}
vec_ps operator-(const vec_ps& lhs, const vec_ps& rhs)
{       
    return vec_ps(lhs) -= rhs;
}
vec_ps operator*(const vec_ps& lhs, const vec_ps& rhs)
{       
    return vec_ps(lhs) *= rhs;
}
vec_ps operator/(const vec_ps& lhs, const vec_ps& rhs)
{       
    return vec_ps(lhs) /= rhs;
}
void foo(/*...*/)
{   
        std::vector<float, tbb::cache_aligned_allocator<float>> ref_mu(w*h);
        std::vector<float, tbb::cache_aligned_allocator<float>> cmp_mu(w*h);
        std::vector<float, tbb::cache_aligned_allocator<float>> ref_sigma_sqd(w*h);
        std::vector<float, tbb::cache_aligned_allocator<float>> cmp_sigma_sqd(w*h);
        std::vector<float, tbb::cache_aligned_allocator<float>> sigma_both(w*h);
        int size    = w*h*sizeof(float);
        /*...*/
        float ssim_sum  = 0.0;
        float ssim_sum2 = 0.0;
        vec_ps ssim_sum_ps(0.0f);       
        for(int n = 0; n < size/16; ++n)
        {
            auto ref_mu_ps          = vec_ps::load(ref_mu.data()        + n*4);
            auto cmp_mu_ps          = vec_ps::load(cmp_mu.data()        + n*4);
            auto sigma_both_ps      = vec_ps::load(sigma_both.data()    + n*4);
            auto ref_sigma_sqd_ps   = vec_ps::load(ref_sigma_sqd.data() + n*4);
            auto cmp_sigma_sqd_ps   = vec_ps::load(cmp_sigma_sqd.data() + n*4);
            auto numerator   = (2.0f * ref_mu_ps * cmp_mu_ps + C1) * (2.0f * sigma_both_ps + C2);
            auto denominator = (ref_mu_ps*ref_mu_ps + cmp_mu_ps*cmp_mu_ps + C1) * (ref_sigma_sqd_ps + cmp_sigma_sqd_ps + C2);
            ssim_sum_ps += numerator / denominator; 
        }
        for(int n = 0; n < 4; ++n)
            ssim_sum2 += ssim_sum_ps.value.m128_f32[n];
        for (int y = 0; y < h; ++y)
        {
            int offset = y*w;
            for (int x = 0; x < w; ++x, ++offset) 
            {           
                float numerator   = (2.0f * ref_mu[offset] * cmp_mu[offset] + C1) * (2.0f * sigma_both[offset] + C2);
                float denominator = (ref_mu[offset]*ref_mu[offset] + cmp_mu[offset]*cmp_mu[offset] + C1) * (ref_sigma_sqd[offset] + cmp_sigma_sqd[offset] + C2);
                ssim_sum += numerator / denominator;                
            }
        }
        assert(ssim_sum2 == ssim_sum); // FAILS!
}