Hello!
I need two procs: converting from double fpu to string and back.
I will be very glad if you give me a good realisations of these procs.
Thank you.

You can use C's printf, or if you share FASMers' spirit, you can create your own. You can also check out the Example & Tutorial section. Lots of examples there. Good luck.

Depending on requirements, this is often a non-trivial task... in my own library, I implemented the http://www.cs.indiana.edu/~dyb/pubs/FP-Printing-PLDI96.pdf method, which is slower than the "standard method" but provides string <-> double <-> string <-> double without rounding/loss issues (a messy but required bit that I needed).

The guts of mine are from_double and to_double at https://2ton.com.au/library_as_html/string32.inc.html

Cheers