The parser records where the integer digits, the fraction digits, and the
exponent of a float token are. For doubles with at most 19 digits, the
value is now read from that layout: the digits eight at a time, without
scanning the token, and rounded with Clinger's fast path where both
operands are exact, else with the Eisel-Lemire algorithm (which needs no
fallback for up to 19 digits). Both round correctly, so the values are
those of parse(); other tokens and types keep the library's conversion.
get<double>(), materialize(), dump(), and comparisons use it. Traversing
canada.json (111,000 floats, every number converted): 0.53 -> 0.86 GB/s.
Tests add tokens around the limits (19 and 20 digits, 2^53, 10^22) to the
bit-for-bit comparison with parse().
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
get<T>() of arithmetic types is inlined down to the conversion, so that
its checks of the node kind merge with those of the caller, and reading
an integer needs no call. Traversing every value: citm_catalog -6%,
marine_ik -5%, numbers and twitter -3%, mesh -2.5%, canada -1% (and
more above the float conversion from the digit layout: citm_catalog
-14%, marine_ik -11%).
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
basic_json_view gains get<T>(), get_to(), value() with keys and JSON
pointers, and operator[], at(), and contains() with JSON pointers, plus
two functions basic_json has no counterpart for:
- get_string(): the string without a copy (a string_view into the source,
or into the decoded strings for strings with escapes)
- number_token(): the text of a number as it appears in the source
get<T>() converts arithmetic types, strings (also string_view_t),
std::nullptr_t, std::vector, maps with string keys, and views directly;
floats are converted from the digit layout recorded by the parser with the
library's conversion chain, so the values are bit-identical to parse().
Other types, including user types with from_json(), go through
materialize().
The exceptions are those of basic_json, message included. Where const
basic_json has undefined behavior (a missing key or an index out of range
with operator[] and a JSON pointer), the result is a discarded view;
value() returns the default wherever basic_json catches out_of_range, and
contains() never throws. Array indices of JSON pointers follow
json_pointer's rules (parse_error.106/109, out_of_range.404/410).
Tests compare the conversions of 2,000 generated documents, 20,000 float
tokens (double and float, bit for bit), and every JSON pointer of 1,000
documents with basic_json, and the exceptions for malformed pointers.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
