I don't see great problem to write this algorithm in B4A language.
The core of all is here: In natural language it calculates: size + 64bit chksum of the first and last 64k (even if they overlap because the file is smaller than 128k)
So, you need to start with a Long variabile (64 bit), initialize it with file.lenght, then use a FOR on the first 64KB, the another FOR on the last 64KB and add the checksum.
What is the language that you know well ??
In the page there are many example for to understand how to write it.
I see that there is also a file for download (breakdance.avi movie) for to test if the program works.
Start to write some code and then we can help you
Sergio