With seekable input, the lexer derives line and column on demand (#5809)
by counting the newlines in all input consumed so far. A SAX parser that
recovers from errors asks for the position once per error, so input with
an error at every character took quadratic time: "{" followed by 100000
commas took 85 s at -O0, and the parser tests timed out under Valgrind
(1500 s, was 69 s on develop).
get_position() now remembers what it counted and only scans the input
consumed since the previous call; count_consumed_lines() takes the start
of the range. The 100000 commas now take 0.17 s, unit-class_parser 0.9 s
instead of 86 s. Over 69284 error messages from random multi-line inputs,
the messages are identical to those before the change.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Niels Lohmann
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