BSON stores an array as a document whose keys are the decimal indices. Both
passes built that key with std::to_string() and copied it into a string_t for
every element, and the size pass then validated it like an object key (a
search for U+0000 and the UTF-8 handler), though a decimal number cannot fail
either.
The index name now lives in the array's frame as digits that are incremented
in place, and the size pass adds 2 + the number of digits.
Instructions per call (Linux, GCC 13, thousands), to_bson: 20000 integers 16228 -> 6486, 20000 floats 16304 -> 6562, canada 109155 -> 55282, 20000 small objects 45513 -> 37171, citm_catalog 17269 -> 15026.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Niels Lohmann
135095d692