""" uint32_t a = ..., b = ...; uint32_t res = a + b; uint32_t carry = res < a; """ But note well: this trick doesn't work when there is also a

""" uint32_t a = ..., b = ...; uint32_t res = a + b; uint32_t carry = res < a; """ But note well: this trick doesn't work when there is also a carry-in. That is, uint32_t res = a + b + carry; carry = res < a; won't work when b = 0xFFFFFFFF and carry = 1, so you have to check for carries twice, or set `carry = res < a || (res == a && carry);` or similar. So if you are implementing bignums on an architecture that doesn't have ADC (such as RISC-V), or on a vector architecture where the performance would be bad, then you often need an alternative strategy such as using less than 32/64 bits per limb (whether that's half-size, or 30 bits or 51 bits or whatever).