2.3 hour duration gives 2h 17m (should be 2h 18m)

[afanasy]

//moment.js 2.11.2
moment.duration(0.3, 'h').minutes()
//18, as expected
moment.duration(2.3, 'h').minutes()
//17
//?!?

I understand that it's floating point problem, but can we work around this somehow, by not converting everything to milliseconds for instance?

[icambron]

Yeah, that seems like a bug. Caused by this, I assume:

> moment.duration(2.3, 'h').asMilliseconds()
8279999.999999999

[mattjohnsonpint]

Oh JavaScript floating point numbers, you're so funny...

2.3 * 60 * 60 * 1000 === 8280000
60 * 60 * 1000 === 3600000
2.3 * 3600000 === 8279999.999999999

WAT.

[mattjohnsonpint]

Actually I think this one may require some more detailed thought in how we apply large constants against multiplication and division. Probably not ideal for up-for-grabs, but if you think you have a good approach, still send a PR. Be sure to include a unit test with at least the above example.

[afanasy]

@mj1856 Initially the approach I'd take is to store duration values with units and use them directly for conversions in .units() calls, w/o converting to ms.

//2.3 hours to minutes
//current 2.11.2 version
2.3 * 3600000 / 60000 === 137.99999999999997 //minutes - wrong
//proposal
2.3 * 60 === 138 //minutes - correct

but now I don't know, may be it will produce new errors with some other floating point numbers, is it really the problem with division and/or large constants?

[mattjohnsonpint]

Note how there was no division in my examples.

[afanasy]

Then may be we should use some lib (or corresponding code subset) like https://github.com/infusion/Fraction.js for this?

[icambron]

Eh, floating point numbers are just painful in general. FWIW, Java behaves exactly like Matt's "WAT" example.

I propose we just change this line to

hours * 3600 * 1000

Does that suffice?

[mattjohnsonpint]

Works for me. We should have a test for that as well, as I could see someone accidently putting it back during a future cleanup.

Are there other areas like this?

[mnt]

Sorry I might be wrong but while playing around:
actual result:

4.1 * 3600 * 1000 === 14759999.999999998
4.17123 * 1000 * 60 * 60 === 15016428.000000002

expected result:

4.1 * 3600 * 1000 === 14760000
4.17123 * 1000 * 60 * 60 === 15016428

Perhaps a way to fix this is to make all floating point numbers to integers. Then dividing by the multiplier afterwards ?

(4.1 * 10 * 3600 * 1000) / 10 === 14760000
(4.17123 * 100000 * 1000 * 60 * 60) / 100000 === 15016428

[afanasy]

@mnt Looks interesting, but doesn't work for me for

(4.17123 * 100000 * 1000 * 60 * 60) / 100000
//outputs 15016428.000000002 in Google Chrome console

but still may be it covers more cases