Benchmark results on my machine (Core i5-4200M):
running 16 tests
test check ... ignored
test test_fast_newlines ... bench: 2,175 ns/iter (+/- 57)
test test_fast_nonewlines ... bench: 2,175 ns/iter (+/- 348)
test test_fast_somenewlines ... bench: 16 ns/iter (+/- 3)
test test_faster_newlines ... bench: 2,944 ns/iter (+/- 416)
test test_faster_nonewlines ... bench: 2,946 ns/iter (+/- 76)
test test_faster_somenewlines ... bench: 25 ns/iter (+/- 6)
test test_fastest_newlines ... bench: 1,283 ns/iter (+/- 210)
test test_fastest_nonewlines ... bench: 1,283 ns/iter (+/- 357)
test test_fastest_somenewlines ... bench: 14 ns/iter (+/- 3)
test test_screaming_newlines ... bench: 1,180 ns/iter (+/- 290)
test test_screaming_nonewlines ... bench: 1,180 ns/iter (+/- 17)
test test_screaming_somenewlines ... bench: 10 ns/iter (+/- 2)
test test_slow_newlines ... bench: 5,695 ns/iter (+/- 1,304)
test test_slow_nonewlines ... bench: 3,725 ns/iter (+/- 463)
test test_slow_somenewlines ... bench: 29 ns/iter (+/- 1)
test result: ok. 0 passed; 0 failed; 1 ignored; 15 measured
I should note that this machine does have POPCNT, though it does not appear to make any difference. Please run the benchmark on your machine and report your finding as an issue on this project. Thank you!