What do these Xcursor names mean?

I have a plan to make my own Xcursor theme. I'm looking at existing themes and found some strange names such as 08e8e1c95fe2fc01f976f1e063a24ccd. I found a piece of code that contain this name. https://vimsky.com/examples/detail/cpp-ex---QHash-reserve-method.html According to the comment, it seems to be an MD5 hash of something hardcoded. But I failed to produce this hash. Which programs need these names? All the themes installed on my system are symbolic links to these names, but I can't find any documentation for this. And there are two cursors named size_bdiag for top-right/bottom-left window resizing and size_fdiag for top-left/bottom-right window resizing. But I failed to understand what these names mean. Maybe 'diag' means 'diagonal' but still I can't guess what 'b' and 'f' mean. I googled several times but I can't find any documentation. Do those have no meaning? Is the original author just playing with me?