[racket] numbers/bytes in r6rs

At Sun, 26 Dec 2010 09:52:20 +0100, Wolfgang De Meuter wrote:
> I'm struggling with chapter 2 of the R6RS libraries (relation between Scheme 
> data objects and bytevectors). Does anyone know a clean&simple way for
> - determining the number of bytes needed to push an arbitrary-sized number in a 
> bytevector;  (log nbr 256) is not good enough :-)

`bitwise-length' ? 

> - determining whether a floating point number is a double or a single.

I don't think there's any predicate for that.