Source code of Bashicu matrix calculator is now available at GitHub repository. The main program is basmat.c and there is a Reader's guide of the source code because the definition of Bashicu Matrix is written in the C code.
The web interface internally uses this C program with some limitations on parameters. You can follow the installation instruction and run the offline version on your PC. In this way you can run the program up to the limit of your system resources and time.
Bashicu Matrix Calculator (offline version) by Fish