Bug #15023: Time precision (in microsecond) inaccurate after performing strftime

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-darwin17]
• Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN

[calvinchso (Calvin So)]

Please see the example below. I think we should expect the result to be "1486525793.995". Right?

OS version: MacOS High Sierra 10.13.6

Ruby version: 2.5.1

2.5.1 :005 > Time.at(1486525793.995).strftime("%s.%6N")
 => "1486525793.994999"

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Rejected

IEEE 754 floating point numbers are inexact, and cannot represent that value exactly.

printf("%.20f\n", 1486525793.995) #=> 1486525793.99499988555908203125

You can use the second argument to Time.at if you have accurate fraction seconds.

puts Time.at(1486525793, 995_000).strftime("%s.%6N") #=> 1486525793.995000

[nobu (Nobuyoshi Nakada)]

Time.at supports Rational numbers too.

puts Time.at(1486525793.995r).strftime("%s.%6N") #=> 1486525793.995000