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It's weird that this is just a side-effect of the way strtol works, but there's no way (that I can figure out) to get + or - involved.

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It can't only be that, or 127.1 would not work. It is doing some parsing beyond just calling a parseInt on each of them in order to recognize domain names and use name resolution rather than directly putting the bytes in the IP header. That must be why 0x9000000.-16250872 doesn't work (if negative worked, that should also resolve to 8.8.8.8).

All of this weird behavior is generally inet_aton. https://linux.die.net/man/3/inet_aton

I looked into this a while back, IIRC BSD added the "omit zeroes" as a nonstandard convenience feature and other OSes copied it. I'm far afk for I'd find my notes on this.

It's not "omit zeroes". It's, "represent the last three octets with just one integer".

127.256 is valid, and would be equivalent to 127.0.1.0. The last integer can be up to 16777215 (2²⁴-1).

Similarly, if you instead include three groups of integers, the first two represents one octet each, and the last represents two. 127.2.256 is equivalent to 127.2.1.0.

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