The compact writer of dump() (cursor in a register, fixed-size copies of
tokens) served dump(-1) only; every dump(indent), and everything with
ensure_ascii that was indented, went through a generic walk that calls put()
for each token and put_repeated() (a memset call) for each line break. The
fast writer now writes indented output, too, with or without ensure_ascii, and
the generic walk is gone. A line break is a copy of a 64-byte ruler (a line
break and 63 indentation characters) when the line is at most 64 bytes, and a
store plus memset beyond that. The depth is counted only in the indented
instantiations (counting it in the compact one cost an editable document 5 %
with Clang). The indented walks are out of line (dump_pretty()): inlined
into dump() next to the compact ones, they made compact dumps of integer
arrays 7 % slower.
A decoded string (one with escape sequences) of a damaged image loaded with
image_check::bounds can contain invalid UTF-8. As before, the compact dump
writes such bytes unchanged, and the indented dump throws type_error.316; its
runs are found by the lexer's validating scan (a scalar validation of every
sequence made dump(2) of decoded CJK text twice as slow as before).
dump(2) instructions per call, macOS arm64 (before -> after):
twitter citm canada jeopardy(4k)
json 3.75M -> 1.85M 8.28M -> 3.93M 67.1M -> 56.0M 9.56M -> 4.81M
editable 3.82M -> 1.84M 8.48M -> 4.02M 68.1M -> 56.2M 9.66M -> 4.75M
Linux instructions (GCC 13 / Clang 18), dump(2) and dump(2, ' ', true):
twitter -25 % / -30 % -11 % / -11 %
citm -29 % / -28 % -24 % / -24 %
jeopardy(4k) -25 % / -32 % -20 % / -24 %
CJK text with \u escapes -6 % / -11 % -2 % / -2 %
The compact dump is unchanged (within +0.4 % on Linux, within noise on the Mac).
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Niels Lohmann
ef45593bda