Another simple bit-twiddling-hack (it has a proper name which I unfortunately forgot) is SIMD without SIMD instructions by masking out the top-level bits (which are essentially the carry-flags), e.g. doing eight 7-bit additions at once:

    uint64_t a = ((a0 & 0x7F) | ((a1 & 0x7F)<<8) ...;
    uint64_t b = ((b0 & 0x7F) | ((b1 & 0x7F)<<8) ...;
    uint64_t c = (a + b) & 0x7F7F7F7F7F7F7F7F;