AS3 charset charset detecting library

Question

Is there any library to detect charset of the string?

Here is how i'm converting strings

var b:ByteArray = new ByteArray();
b.writeMultiByte(str,to_charset);
return b.toString();

The problem starts when str is already windows-1251 and to_charset is windows-1251 as well. After second conversion it's doing something strange:

Русский -> Ðóññêèé

http://www.artlebedev.ru/tools/decoder/

Decoder here shows Ðóññêèé it's CP1252 → CP1251