Returns x such that incomplete_gamma(a, x) = y. It could be implemented by searching for the only root of a monotonic function on (0, infinity).

see gammaincinv

Seen with @arnetheduck.

for uint128, stint properly generates add + adc (see status-im/nim-stint#10)

But for uint256+, the way carry is done will loop multiple time on the low half
https://github.com/status-im/nim-stint/blob/9993b9dca4a2dbf76bc432252ad4e8db944ae831/stint/private/uint_addsub.nim#L17-L29

Important for WASM codesize optimization.