One day while trawling through the Java language documentation, as you do, I found this little beauty lurking within Double:
0.25 == 0x1.0p-2
Now, obviously (!) this means take the number hexadecimal 1 and right shift it decimal 2 times. The rule seems to be to use base 16 on the integer side and base 2 on the real side.
Has anyone out there actually used the right hand syntax in a necessary context, not just as a way getting beers out of your fellow developers?