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### 946. `duration_cast` improperly specified

Section: 27.5.8 [time.duration.cast] Status: NAD Submitter: Pete Becker Opened: 2008-12-20 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

27.5.8 [time.duration.cast]/3:

> .... All intermediate computations shall be carried out in the widest possible representation... .

So ignoring floating-point types for the moment, all this arithmetic has to be done using the implementation's largest integral type, even if both arguments use `int` for their representation. This seems excessive. And it's not at all clear what this means if we don't ignore floating-point types.

This issue is related to 952.

[ Howard adds: ]

> The intent of this remark is that intermediate computations are carried out using:

> >     common_type<typename ToDuration::rep, Rep, intmax_t>::type

> The Remark was intended to be clarifying prose supporting the rather algorithmic description of the previous paragraph. I'm open to suggestions. Perhaps the entire paragraph 3 (Remarks) would be better dropped?

[ Batavia (2009-05): ]

> We view this as a specific case of issue 952, and should be resolved when that issue is resolved.

> Move to NAD.

Proposed resolution: