>> 52 bits of significand.

As I sit listening to Professor Kahan on tape while reading "52", I see
on the other monitor the number 53.  The larger number is actually the
right one, despite the fact that 53+11+1 > 64, because, for normal
numbers, the leading bit of the significand is boring.  It is always on.
That's what normalization does, after all.  Since it is so boring, we
need not even store it.

Dick