* doublest.c (FLOATFORMAT_LARGEST_BYTES): New define.

* doublest.c (FLOATFORMAT_LARGEST_BYTES): New define.
(get_field, put_field): Assert that the format is one we can handle.
Simplify logic accordingly.
(floatformat_normalize_byteorder): New function.
(convert_floatformat_to_doublest): Use floatformat_normalize_byteorder
to normalize and select modified byte order. Pass modified byte order
to get_field.
(floatformat_is_negative, floatformat_is_nan, floatformat_mantissa):
Likewise.
(convert_doublest_to_floatformat): Select an appropriate intermediate
byte order if necessary.  Always convert to the final format before
returning.