horizontal sum of 8 packed 32bit floats [duplicate]

Answer 1

union ymm {
    __m256 m256;
    struct {
        __m128 m128lo;
        __m128 m128hi;
    };
};

union ymm result = {1,2,3,4,5,6,7,8};
__m256 a = {9,10,11,12,13,14,15,16};

result.m256 = _mm256_add_ps (result.m256, a);
result.m128lo = _mm_hadd_ps (result.m128lo, result.m128hi);
result.m128lo = _mm_hadd_ps (result.m128lo, result.m128hi);
result.m128lo = _mm_hadd_ps (result.m128lo, result.m128hi);