This library exist, the author Aleksey Vaneev is basically a DSP greek semi-god.https://github.com/avaneev/r8brain-free-srcBy the same author: https://github.com/avaneev/avir
Hm, looks like an upsampled sinc filter. Have you compared it to these?
https://ccrma.stanford.edu/~jos/resample/Free_Resampling_Software.html
