chars_format::javascript follows the strict-mode grammar, which rejects
any leading zero. In sloppy mode, JavaScript also accepts a leading zero
when one of the digits is 8 or 9 ("08.5" is 8.5, Annex B's
NonOctalDecimalIntegerLiteral). A leading zero followed only by octal
digits is a LegacyOctalIntegerLiteral ("0775"), which is not a decimal
number: it is rejected with the new parse_error::legacy_octal_integer_part
so the caller can parse it in base 8.
javascript_sloppy sets one extra bit on top of javascript, and the check
lives inside the existing runtime JavaScript branch of
parse_number_string<false>, so the general path is unchanged. An
interleaved A/B with realbenchmark on canada.txt and mesh.txt (ASCII and
UTF-16, 32/64-bit) shows identical instructions per float and cycles
within noise.
Document both formats in the README.
The JSON format rejects leading zeros, which JavaScript also rejects,
but it further requires digits on both sides of the decimal point,
which JavaScript does not: ".5", "5." and "5.e3" are all valid
DecimalLiteral productions. Users lexing JavaScript therefore could not
use chars_format::json and had to re-check the integer span themselves
after a general-mode parse.
chars_format::javascript is general mode plus the leading-zero rule
(reported as leading_zeros_in_integer_part), with no_infnan. It is a
runtime check on the format, like fortran, so it reuses the existing
parse_number_string<false> instantiation. A leading minus sign is
accepted, and a leading plus sign with allow_leading_plus.
Claude-Session: https://claude.ai/code/session_01KbAWRBpE3MPy5cXECc5vWZ
