"it would be quicker to tell us what it does, then write *that* for you."

Yes, that'd be my approach.

One way to do this is to put comments alongside the assembler which describe what it's doing in a C-like "pseudo code"
Then implement your "pseudo code" in real 'C'.

This, of course, requires that you understand the assembler - hence my original question!

Lots of different coloured highlighter pens can also be invaluable!