Issue #16470 has been updated by mame (Yusuke Endoh).


Interesting, I can reproduce the performance difference:

```
$ time ./miniruby -e '100000.times { Time.utc(2007, 11, 1, 15, 25, 0, 123456.789.to_r) }'

real    0m0.633s
user    0m0.622s
sys     0m0.011s

$ time ./miniruby -e '100000.times { Time.utc(2007, 11, 1, 15, 25, 0, 123456.789.rationalize) }'

real    0m0.607s
user    0m0.587s
sys     0m0.020s
```

Note that `#to_r` is 10 times faster than `#rationalize`:

```
$ time ./miniruby -e '100000.times { 123456.789.to_r }'

real    0m0.059s
user    0m0.039s
sys     0m0.020s

$ time ./miniruby -e '100000.times { 123456.789.rationalize }'

real    0m0.598s
user    0m0.587s
sys     0m0.010s
```

I think that this is because `#to_r` produces relatively big denominator, which makes addition slower during `Time.utc` calculation.

(I have no opinion about the `Time.utc` issue itself.  Sorry.)

----------------------------------------
Feature #16470: Issue with nanoseconds in Time#inspect
https://bugs.ruby-lang.org/issues/16470#change-86297

* Author: andrykonchin (Andrew Konchin)
* Status: Open
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
----------------------------------------
Ruby 2.7 added nanosecond representation to the return value of `Time#inspect` method.

Nanosecond is displayed as `Rational` as in the following example:

```ruby
t = Time.utc(2007, 11, 1, 15, 25, 0, 123456.789)
t.inspect # => "2007-11-01 15:25:00 8483885939586761/68719476736000000 UTC"
```

The nanosecond value `8483885939586761/68719476736000000` can be expanded to `0.12345678900000001`. This is different from the stored nanosecond:

```ruby
t.nsec # => 123456789
t.strftime("%N") # => "123456789"
```

I assume it isn't expected, and will be fixed.



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