XmStringByteCompare(3) on Linux
The text e88e8f89a16c, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A compound string function that indicates the results of a byte-by-byte comparison "XmStringByteCompare" "compound string functions" "XmStringByteCompare"