How to calculate the x in 1/x format when all i got is decimal floating point representation of the shutter speed ( for example 0.0101316 and possibly other data in exif )?
Just invert and then round to the nearest "well known" shutter speed - e.g. 0.0101316s = (just about) 1/98 s, and then round to 1/100 s.
You'll probably need a table of shutter speeds to look up into as the traditional speeds aren't quite a geometric progression. This answer contains a list of the standard shutter speeds (for both half and third stop increments), but note that my 550D flips over to the "0.3 s" notation at that point, rather than at 1 s as in the table (i.e. a shutter speed of 0.25 s is displayed as
4 in the viewfinder and
1/4 in playback, but 0.3 s is displayed as
0"3 in both the viewfinder and playback). Other cameras may vary on this point.