From: sawadatsuyoshi@...
Date: 2014-08-15T00:48:54+00:00
Subject: [ruby-core:64373] [ruby-trunk - Bug #10135] Time.at is inaccurate

Issue #10135 has been updated by Tsuyoshi Sawada.


Your way of presentation may not be clear. I suppose the division is irrelevant here. Your point seems to be that while `to_f` is idempotent with:

~~~ruby
    1381089302.195.to_f
    #=> 1381089302.195
~~~

it is not idempotent with:

~~~ruby
    Time.at(1381089302.195).to_f
    #=> 1381089302.1949997
~~~

----------------------------------------
Bug #10135: Time.at is inaccurate
https://bugs.ruby-lang.org/issues/10135#change-48342

* Author: John Smart
* Status: Open
* Priority: High
* Assignee: ruby-core
* Category: 
* Target version: current: 2.2.0
* ruby -v: ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-darwin13.0]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN
----------------------------------------
I believe I have found an issue with Time.at.  Many runtimes and DBs use milliseconds since epoch for recording time.  Currently, the only way to generate a Time in ruby with milliseconds is:

~~~
Time.at(milliseconds / 1000.0)
~~~

However, this is inaccurate:

~~~
> Time.at(1381089302195 / 1000.0).to_f
=> 1381089302.1949997
> Time.at(1381089302195 / 1000.0).strftime('%3N')
=> "194"
~~~

This doesn't make much sense because you would expect:

~~~
> 1381089302195 / 1000.0
=> 1381089302.195
> (1381089302195 / 1000.0).to_f
=> 1381089302.195
~~~

It seems that somewhere in the MRI, someone is using floating-point math to represent a Time.

Is there any other way (workaround) to construct Time with millisecond accuracy?




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