# Re: [css-values] Rounding a real number to an integer

From: Simon Fraser <smfr@me.com>
Date: Tue, 18 Dec 2018 22:29:38 -0800
Message-Id: <8770E66E-A85F-443F-B3E7-CCB512CAE7F7@me.com>
Cc: fantasai <fantasai.lists@inkedblade.net>, W3C www-style mailing list <www-style@w3.org>
To: Gérard Talbot <www-style@gtalbot.org>
```> On Dec 18, 2018, at 6:15 PM, Gérard Talbot <www-style@gtalbot.org> wrote:
>
> Le 2018-12-18 19:58, fantasai a écrit :
>> On 12/15/18 6:46 PM, Gérard Talbot wrote:
>>> Le 2018-12-15 19:46, Gérard Talbot a écrit :
>>>> Hello,
>>>> "
>>>> (...) interpolation happens in the real number space as for <number>s,
>>>> and the result is converted to an <integer> by rounding to the nearest
>>>> integer, with *_values halfway between adjacent integers rounded
>>>> towards positive infinity_*.
>>>> "
>>>> CSS4 Values, section 5.1.1. Combination of <integer>
>>>> https://www.w3.org/TR/css-values-4/#combine-integers
>>>> So
>>>> 'z-index: -1.5'
>>>> should be converted to 'z-index: -1' and not to 'z-index: -2'
>>>> while
>>>> 'z-index: 1.5'
>>>> should be converted to 'z-index: 2'.
>>> Oops.. I meant
>>> 'z-index: calc(-1.5)'
>>> should compute to 'z-index: -1' and not to 'z-index: -2'
>>> while
>>> 'z-index: calc(1.5)'
>>> should compute to 'z-index: 2'.
>>>> Is my interpretation of the spec correct?
>> Afaict it is correct. If that's not what implementations do,
>> though, let us know as we may need to adjust the spec. :)
>> ~fantasai
>
> Firefox 66 buildID=20181218191030 resolves 'z-index: calc(-3 / 2)' to 'z-index: -2' not as 'z-index: -1' in:
> http://www.gtalbot.org/BrowserBugsSection/CSS3Values/calc-negative-fraction-001.html
>
> Chromium 73.0.3645.0 passes (false positive)
> http://www.gtalbot.org/BrowserBugsSection/CSS3Values/calc-negative-fraction-001.html
> but that is because 'z-index: calc(-3 / 2)' is not resolved, is not handled at all.
>
> - - - - -
>
> Chromium 71, Chromium 73.0.3645.0 and Epiphany 3.31.3-3-g64a3330ce (WebKitGTK+ 2.23.1) fail
> http://www.gtalbot.org/BrowserBugsSection/CSS3Values/calc-positive-fraction-001.html
>
> Firefox 66 buildID=20181218191030 passes
> http://www.gtalbot.org/BrowserBugsSection/CSS3Values/calc-positive-fraction-001.html <http://www.gtalbot.org/BrowserBugsSection/CSS3Values/calc-positive-fraction-001.html>

Be careful with your test case. Chrome and WebKit treat the calc as invalid (for some reason they don’t accept <number> / <number>), so the used value for z-index ends up as auto, but your testcase shows green in that case.

Simon
```
Received on Wednesday, 19 December 2018 06:30:03 UTC

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