static
void
test_add(uint8_t acc[4], uint8_t addend[4])
{
    uint8_t carry = 0;
    for (int i = 0; i < 4; ++i)
    {
        acc[i] = acc[i] + addend[i] + carry;
        carry = (acc[i] < addend[i]); // RISCV overflow check
    }
}