basic_json stores number_integer and number_unsigned in a union, and
number_unsigned_t only has to be at least as wide as number_integer_t
(with the default types, both are 64-bit and have the same
representation). When number_integer_t is narrower, write_msgpack()
read the wrong union member in two places:
- The number_unsigned case wrote number_integer's bits instead of
number_unsigned's, silently writing the wrong value whenever it
did not fit in number_integer_t.
- The number_integer case (non-negative branch) picked the encoded
width by comparing number_unsigned's bits, which is undefined
behavior, though the value written was still number_integer's, so
at worst a too-wide encoding was chosen.
Read the active member in both cases, like the other binary writers
(CBOR, UBJSON, BJData, BSON, BON8) already do.
Fixes#5644.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Niels Lohmann
4b027c9ea3