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Niels Lohmann
4cad4e08a4
dump_escaped called std::snprintf(..., "\u%04x", ...) once per escaped code point in the string serialization hot path. snprintf re-parses the format string and pulls in locale/printf machinery on every call, which is far heavier than the fixed 6-/12-byte output warrants. This is hot for any string containing control characters, and for all non-ASCII text when ensure_ascii is set. Replace it with write_u_escape, a small helper that writes the escape directly into string_buffer via a nibble-to-hex lookup table, mirroring the existing hand-rolled dump_integer fast path in the same file. Signed-off-by: Niels Lohmann <mail@nlohmann.me>