json_document::parse(FILE*) (and read(), accept(), parse_copy()) went through the
library's file input adapter and appended the text character by character
with fgetc. Read it with fread in blocks instead, like the std::istream
overload already does.
Parsing citm_catalog.json (1.7 MB) from a FILE*:
Apple M1: 80.6 M -> 8.4 M instructions, 4.8 ms -> 0.55 ms (parse of the same text from a std::string: 8.7 M)
Linux x86-64 Ir (whole run), GCC 13 / Clang 18: 47.0 M -> 13.7 M / 45.8 M -> 14.2 M
The parsed documents and the error cases are identical (checked over the test corpus
and 30 mutants of each file). A null FILE* is handled as before (by the library's adapter).
Belongs to the PR "json_view: read-side speedups".
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Niels Lohmann
c9deb30150