Care to explain and show the details?

"Extraordinary claims require extraordinary evidence."

Your original claim "I've not checked but this guy, and by extension the C++ standards committee who worked on this new API, are probably full of shit" was pretty extraordinary.

Look at the compiler-generated instructions yourself if you don't believe the source that I linked; in the cases I've seen all the extra new stuff just adds another layer on top of existing functions and if the former are faster the latter must necessarily also be.

The standards committee's purpose is to justify their own existence by coming up with new stuff all the time. Of course they're going to try to spin it as better in some way.

How not?

It compiles from sources, can be better in-lined, benefits from dead code elimination when you don't use unusual radix. It also don't do locale based things.

I wrote this library once; https://github.com/ton/fast_int.

Removed `std::atoi` from the benchmarks since it was performing so poorly; not a contender. Should be easy to verify.

Rough results (last column is #iterations):

  BM_fast_int<std::int64_t>/10                  1961 ns         1958 ns       355081
  BM_fast_int<std::int64_t>/100                 2973 ns         2969 ns       233953
  BM_fast_int<std::int64_t>/1000                3636 ns         3631 ns       186585
  BM_fast_int<std::int64_t>/10000               4314 ns         4309 ns       161831
  BM_fast_int<std::int64_t>/100000              5184 ns         5179 ns       136308
  BM_fast_int<std::int64_t>/1000000             5867 ns         5859 ns       119398
  BM_fast_int_swar<std::int64_t>/10             2235 ns         2232 ns       316949
  BM_fast_int_swar<std::int64_t>/100            3446 ns         3441 ns       206437
  BM_fast_int_swar<std::int64_t>/1000           3561 ns         3556 ns       197795
  BM_fast_int_swar<std::int64_t>/10000          3650 ns         3646 ns       188613
  BM_fast_int_swar<std::int64_t>/100000         4248 ns         4243 ns       165313
  BM_fast_int_swar<std::int64_t>/1000000        4979 ns         4973 ns       140722
  BM_atoi<std::int64_t>/10                     10248 ns        10234 ns        69021
  BM_atoi<std::int64_t>/100                    10996 ns        10985 ns        63810
  BM_atoi<std::int64_t>/1000                   12238 ns        12225 ns        56556
  BM_atoi<std::int64_t>/10000                  13606 ns        13589 ns        51645
  BM_atoi<std::int64_t>/100000                 14984 ns        14964 ns        47046
  BM_atoi<std::int64_t>/1000000                16226 ns        16206 ns        43279
  BM_from_chars<std::int64_t>/10                2162 ns         2160 ns       302880
  BM_from_chars<std::int64_t>/100               2410 ns         2407 ns       282778
  BM_from_chars<std::int64_t>/1000              3309 ns         3306 ns       208070
  BM_from_chars<std::int64_t>/10000             5034 ns         5028 ns       100000
  BM_from_chars<std::int64_t>/100000            6282 ns         6275 ns       107023
  BM_from_chars<std::int64_t>/1000000           7267 ns         7259 ns        96114
  BM_fast_float<std::int64_t>/10                2670 ns         2666 ns       262721
  BM_fast_float<std::int64_t>/100               3547 ns         3542 ns       196704
  BM_fast_float<std::int64_t>/1000              4643 ns         4638 ns       154391
  BM_fast_float<std::int64_t>/10000             5056 ns         5050 ns       132722
  BM_fast_float<std::int64_t>/100000            6207 ns         6200 ns       111565
  BM_fast_float<std::int64_t>/1000000           7113 ns         7105 ns        98847