Niels Lohmann cc946adf68 Find the end of the plain run of a decoded string 16 bytes at a time with SSE2 ...

The strings of a document that had escape sequences are written in runs
without a quote, backslash, or control character; the compact dump found the
end of a run 8 bytes at a time with a SWAR test. With SSE2 (x86-64) it now
compares 16 bytes per step. NEON keeps the SWAR code: there the mask of a
step costs more than it saves on the short runs that are typical here.

Instructions of dump(), Linux (GCC 13 / Clang 18):

  twitter.json                  1.99M -> 1.88M (-5.2 %) / 1.97M -> 1.92M (-3.0 %)
  CJK text with \u escapes      5.98M -> 4.52M (-24.5 %) / 5.30M -> 4.25M (-19.9 %)
  ASCII text with a few escapes 4.28M -> 4.09M (-4.4 %) / 4.24M -> 4.11M (-3.2 %)
  jeopardy (4,000 questions)    5.08M -> 4.78M (-5.8 %) / 4.97M -> 4.80M (-3.4 %)

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

2026-10-22 09:30:39 +02:00

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nlohmann

Find the end of the plain run of a decoded string 16 bytes at a time with SSE2

2026-10-22 09:30:39 +02:00