Take the string tree out behind the shed and shoot until dead.
It's possible it's CRC32 with an exceptionally bad choice of polynomial, but it looks broken in am extremely BYOND way (everything being truncated into shorts).
Ahh, fair enough. For what it's worth, then, I've used the following (boost) with nothing but success for all of my BYOND-related projects: https://github.com/kevans91/Savefile/blob/master/src/crc.h