[snip]
>
>>... Hence, log10(2^52) yields 15.65 digits of precision.
>
>This is incorrect, because any mantissa+exponent rapresentation have the first bit of mantissa set to
>1, but it is not stored on the memory.
>Hence log10(2^(52+1)) -> 15.95
[snip]

Fabio,
I forgot the (so called) ghostbit
Sorry