Converting an Integer into Human Readable String

[Nordlöw]

I looking for the function that prints file size on the mode-line in 
size-indication-mode. I have searched for size-indication-mode in the source 
but cannot find a code-references to it. So where is the function that prints 
for example

22k

when file is approximately 22 kilobytes big?

What about difference between
- kilobytes (kB), 1000 bytes, and
- kibibytes (KiB), 1024 bytes, as defined at

Shouldn't Emacs support both?

This is of course not that hard to write but reinvent the wheel?

http://en.wikipedia.org/wiki/Kibibyte