if (bytes > 0) {
    __m128i       x_0, x_1, x_2, x_3;
    __m128i       t_1;
    const __m128i rot16 =
        _mm_set_epi8(13, 12, 15, 14, 9, 8, 11, 10, 5, 4, 7, 6, 1, 0, 3, 2);
    const __m128i rot8 =
        _mm_set_epi8(14, 13, 12, 15, 10, 9, 8, 11, 6, 5, 4, 7, 2, 1, 0, 3);
    uint8_t partialblock[64];

    unsigned int i;

    x_0 = _mm_loadu_si128((__m128i*) (x + 0));
    x_1 = _mm_loadu_si128((__m128i*) (x + 4));
    x_2 = _mm_loadu_si128((__m128i*) (x + 8));
    x_3 = _mm_loadu_si128((__m128i*) (x + 12));

    for (i = 0; i < ROUNDS; i += 2) {
        x_0 = _mm_add_epi32(x_0, x_1);
        x_3 = _mm_xor_si128(x_3, x_0);
        x_3 = _mm_shuffle_epi8(x_3, rot16);

        x_2 = _mm_add_epi32(x_2, x_3);
        x_1 = _mm_xor_si128(x_1, x_2);

        t_1 = x_1;
        x_1 = _mm_slli_epi32(x_1, 12);
        t_1 = _mm_srli_epi32(t_1, 20);
        x_1 = _mm_xor_si128(x_1, t_1);

        x_0 = _mm_add_epi32(x_0, x_1);
        x_3 = _mm_xor_si128(x_3, x_0);
        x_0 = _mm_shuffle_epi32(x_0, 0x93);
        x_3 = _mm_shuffle_epi8(x_3, rot8);

        x_2 = _mm_add_epi32(x_2, x_3);
        x_3 = _mm_shuffle_epi32(x_3, 0x4e);
        x_1 = _mm_xor_si128(x_1, x_2);
        x_2 = _mm_shuffle_epi32(x_2, 0x39);

        t_1 = x_1;
        x_1 = _mm_slli_epi32(x_1, 7);
        t_1 = _mm_srli_epi32(t_1, 25);
        x_1 = _mm_xor_si128(x_1, t_1);

        x_0 = _mm_add_epi32(x_0, x_1);
        x_3 = _mm_xor_si128(x_3, x_0);
        x_3 = _mm_shuffle_epi8(x_3, rot16);

        x_2 = _mm_add_epi32(x_2, x_3);
        x_1 = _mm_xor_si128(x_1, x_2);

        t_1 = x_1;
        x_1 = _mm_slli_epi32(x_1, 12);
        t_1 = _mm_srli_epi32(t_1, 20);
        x_1 = _mm_xor_si128(x_1, t_1);

        x_0 = _mm_add_epi32(x_0, x_1);
        x_3 = _mm_xor_si128(x_3, x_0);
        x_0 = _mm_shuffle_epi32(x_0, 0x39);
        x_3 = _mm_shuffle_epi8(x_3, rot8);

        x_2 = _mm_add_epi32(x_2, x_3);
        x_3 = _mm_shuffle_epi32(x_3, 0x4e);
        x_1 = _mm_xor_si128(x_1, x_2);
        x_2 = _mm_shuffle_epi32(x_2, 0x93);

        t_1 = x_1;
        x_1 = _mm_slli_epi32(x_1, 7);
        t_1 = _mm_srli_epi32(t_1, 25);
        x_1 = _mm_xor_si128(x_1, t_1);
    }
    x_0 = _mm_add_epi32(x_0, _mm_loadu_si128((__m128i*) (x + 0)));
    x_1 = _mm_add_epi32(x_1, _mm_loadu_si128((__m128i*) (x + 4)));
    x_2 = _mm_add_epi32(x_2, _mm_loadu_si128((__m128i*) (x + 8)));
    x_3 = _mm_add_epi32(x_3, _mm_loadu_si128((__m128i*) (x + 12)));
    _mm_storeu_si128((__m128i*) (partialblock + 0), x_0);
    _mm_storeu_si128((__m128i*) (partialblock + 16), x_1);
    _mm_storeu_si128((__m128i*) (partialblock + 32), x_2);
    _mm_storeu_si128((__m128i*) (partialblock + 48), x_3);

    for (i = 0; i < bytes; i++) {
        c[i] = m[i] ^ partialblock[i];
    }

    sodium_memzero(partialblock, sizeof partialblock);
}