Why the maximum and minimum exp values are 1024 and -1021?:

```
>>> sys.float_info
sys.float_info(max=1.7976931348623157e+308, max_exp=1024,
max_10_exp=308, min=2.2250738585072014e-308, min_exp=-1021,
min_10_exp=-307, dig=15, mant_dig=53, epsilon=2.220446049250313e-16,
radix=2, rounds=1)
```

The values (in double precision) 0 and 2047 are reserved for zero, infinity and NaN (in combination with the fraction), so I was expecting -1022 and 1023...