Niels Lohmann b6f0daf319 Write compact dumps of json_view without a library call per token ...

The default dump() (no indentation, no ensure_ascii) gets its own
writer: the same walk and output, with the write position in a local
variable (stores through char pointers would otherwise force a reload
of the buffer's members after each one), strings and number tokens of
the source copied by fixed-size moves of 32 bytes where the source has
that many bytes left (the buffer keeps 64 bytes of slack), and decoded
strings copied in runs up to the next quote, backslash, or control
character. Documents that are not edited are walked through the node
array in order, so that a frame only needs the end of its container,
and integer tokens are read from the source directly. The innermost
open container is kept in local variables, and the stack holds only
the ones around it; the stack starts in a local array of 32 and moves
to the heap only for deeper nesting (its address does not escape, so
its pointers stay in registers). Dumps of shallow documents thus
allocate only the output, whose first size includes the slack, so it
does not grow just before the end.

The long copies are out of line: otherwise, the compiler merges the
fixed-size moves into the same library call.

These techniques come from the prototype; the writer lost them when the
view was split into pull requests, which made dump() 2 to 3 times
slower.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

2026-09-30 15:09:23 +02:00

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nlohmann

Write compact dumps of json_view without a library call per token

2026-09-30 15:09:23 +02:00