rgb2yuv with sse3

void
videoconvert_convert_matrix8 (VideoConvert * convert, gpointer pixels)
{
    int i;
    guint8 *p = pixels;

    __m128i v_byte1 = _mm_set1_epi32(0x000000ff);
    __m128i v_byte3 = _mm_set1_epi32(0x00ff0000);
    __m128i v_mat_yr = _mm_set1_epi16(47);
    __m128i v_mat_yg = _mm_set1_epi16(157);
    __m128i v_mat_yb = _mm_set1_epi16(16);
    __m128i v_mat_ur = _mm_set1_epi16(-26);
    __m128i v_mat_ug = _mm_set1_epi16(-87);
    __m128i v_mat_ub_vr = _mm_set1_epi16(112);
    __m128i v_mat_vg = _mm_set1_epi16(-102);
    __m128i v_mat_vb = _mm_set1_epi16(-10);

    __m128i cnst128 = _mm_set1_epi16(128);
    __m128i cnst4096  = _mm_set1_epi16(4096);
    __m128i cnst32768 = _mm_set1_epi16((short int)32768);

    __m128i mask2   = _mm_set1_epi32(0x00ff00ff);

    __m128i mask_y1 = _mm_set_epi8((char)128, (char)128, 12, (char)128,   (char)128, (char)128, 8, (char)128,
                    (char)128, (char)128, 4, (char)128,   (char)128, (char)128, 0, (char)128);

    __m128i mask_y2 = _mm_set_epi8((char)128, (char)128, 14,  (char)128,  (char)128, (char)128, 10, (char)128,
                    (char)128, (char)128, 6, (char)128,   (char)128, (char)128, 2, (char)128);

    __m128i mask_u1 = _mm_set_epi8((char)128, 12, (char)128, (char)128,   (char)128, 8, (char)128, (char)128,
                    (char)128, 4, (char)128, (char)128,   (char)128, 0, (char)128, (char)128);

    __m128i mask_u2 = _mm_set_epi8((char)128, 14, (char)128, (char)128,   (char)128, 10, (char)128, (char)128,
                    (char)128, 6, (char)128, (char)128,   (char)128, 2, (char)128, (char)128);

    __m128i mask_v1 = _mm_set_epi8(12, (char)128, (char)128, (char)128,   8, (char)128, (char)128, (char)128,
                    4, (char)128, (char)128, (char)128,   0, (char)128, (char)128, (char)128);

    __m128i mask_v2 = _mm_set_epi8(14, (char)128, (char)128, (char)128,   10, (char)128, (char)128, (char)128,
                    6, (char)128, (char)128, (char)128,   2, (char)128, (char)128, (char)128);

    #pragma omp parallel for
    for (i=0; i<convert->width / 8; i++) {
        __m128i a1, a2, r, g, b, y, u, v, res;

        a1 = _mm_loadu_si128((__m128i *)&p[i*32]);
        a2 = _mm_loadu_si128((__m128i *)&p[i*32 + 16]);

        r = _mm_or_si128(_mm_and_si128(_mm_srli_si128(a1, 1), v_byte1), _mm_and_si128(_mm_slli_si128(a2, 1), v_byte3));
        g = _mm_or_si128(_mm_and_si128(_mm_srli_si128(a1, 2), v_byte1), _mm_and_si128(a2, v_byte3));
        b = _mm_or_si128(_mm_and_si128(_mm_srli_si128(a1, 3), v_byte1), _mm_and_si128(_mm_srli_si128(a2, 1), v_byte3));


        y = _mm_add_epi16(
            _mm_add_epi16(
                _mm_mullo_epi16(r, v_mat_yr),
                _mm_mullo_epi16(g, v_mat_yg)),
            _mm_add_epi16(
                _mm_mullo_epi16(b, v_mat_yb),
                cnst4096));

        y = _mm_and_si128(_mm_srai_epi16(y, 8), mask2);

        u = _mm_add_epi16(
            _mm_add_epi16(
                _mm_mullo_epi16(r, v_mat_ur),
                _mm_mullo_epi16(g, v_mat_ug)),
            _mm_add_epi16(
                _mm_mullo_epi16(b, v_mat_ub_vr),
                cnst32768));

        u = _mm_and_si128(
            _mm_add_epi16(
                _mm_srai_epi16(u, 8),
                cnst128),
            mask2);

        v = _mm_add_epi16(
            _mm_add_epi16(
                _mm_mullo_epi16(r, v_mat_ub_vr),
                _mm_mullo_epi16(g, v_mat_vg)),
            _mm_add_epi16(
                _mm_mullo_epi16(b, v_mat_vb),
                cnst32768));

        v = _mm_and_si128(
            _mm_add_epi16(
                _mm_srai_epi16(v, 8),
                cnst128),
            mask2);


        res = _mm_or_si128(_mm_shuffle_epi8(y, mask_y1), _mm_shuffle_epi8(u, mask_u1));
        res = _mm_or_si128(res, _mm_shuffle_epi8(v, mask_v1));

        _mm_storeu_si128((__m128i *)&p[i*32], res);

        res = _mm_or_si128(_mm_shuffle_epi8(y, mask_y2), _mm_shuffle_epi8(u, mask_u2));
        res = _mm_or_si128(res, _mm_shuffle_epi8(v, mask_v2));

        _mm_storeu_si128((__m128i *)&p[i*32 + 16], res);
    }
}