715127b63d
With std::from_chars we can parse subsecond durations much faster than with std::num_get, as shown in the microbenchmarks below. We were using std::num_get and std::numpunct in order to parse a number with the locale's decimal point character. But we copy the chars from the input stream into a new buffer anyway, so we can replace the locale's decimal point with '.' in that buffer, and then we can use std::from_chars on it. Benchmark Time CPU Iterations ---------------------------------------------------------- from_chars_millisec 158 ns 158 ns 4524046 num_get_millisec 192 ns 192 ns 3644626 from_chars_microsec 164 ns 163 ns 4330627 num_get_microsec 205 ns 205 ns 3413452 from_chars_nanosec 173 ns 173 ns 4072653 num_get_nanosec 227 ns 227 ns 3105161 libstdc++-v3/ChangeLog: * include/bits/chrono_io.h (_Parser::operator()): Use std::from_chars to parse fractional seconds. |
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