GeoHex (https://geohex.org/) v3.2 C99 implementation.
Require: CMake, Make, C99 compiler (gcc, clang)
$ git clone "https://github.com/zeriyoshi/libgeohex.git" "libgeohex"
$ cd "libgeohex"
$ mkdir "build"
$ cd "build"
$ cmake ..
$ make -j"$(nproc)"
$ sudo make install
include geohex/geohex.h
and link -lgeohex