[libcamera-devel] [PATCH v4 1/4] libcamera: utils: Add helper class for std::chrono::duration

[Naushir Patuck]

Hi Jacopo,

Thank you for your review feedback.

On Mon, 24 May 2021 at 12:58, Jacopo Mondi <jacopo at jmondi.org> wrote:

> Hi Naush,
>
> On Mon, May 24, 2021 at 09:48:19AM +0100, Naushir Patuck wrote:
> > A new utils::Duration class is defined to represent a
> > std::chrono::duration type with double precision nanosecond timebase.
> > Using a double minimises the loss of precision when converting timebases.
> > This helper class may be used by IPAs to represent variables such as
> frame
> > durations and exposure times.
> >
> > An operator << overload is define to help with displaying
> > utils::Duration value in stream objects. Currently, this will display
> > the duration value in microseconds.
> >
> > Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> > Reviewed-by: David Plowman <david.plowman at raspberrypi.com>
> > ---
> >  include/libcamera/internal/utils.h | 42 ++++++++++++++++++++++++++++++
> >  src/libcamera/utils.cpp            | 41 +++++++++++++++++++++++++++++
> >  2 files changed, 83 insertions(+)
> >
> > diff --git a/include/libcamera/internal/utils.h
> b/include/libcamera/internal/utils.h
> > index 83dada7cc16c..f536f2267d70 100644
> > --- a/include/libcamera/internal/utils.h
> > +++ b/include/libcamera/internal/utils.h
> > @@ -316,8 +316,50 @@ auto enumerate(T (&iterable)[N]) ->
> details::enumerate_adapter<T *>
> >  }
> >  #endif
> >
> > +class Duration : public std::chrono::duration<double, std::nano>
> > +{
> > +     using BaseDuration = std::chrono::duration<double, std::nano>;
> > +
> > +public:
> > +     Duration() = default;
> > +
> > +     template<typename Rep, typename Period>
> > +     constexpr Duration(const std::chrono::duration<Rep, Period> &d)
> > +             : BaseDuration(d)
> > +     {
> > +     }
> > +
> > +     template<typename Period>
> > +     double get() const
> > +     {
> > +             auto const c =
> std::chrono::duration_cast<std::chrono::duration<double, Period>>(*this);
> > +             return c.count();
> > +     }
> > +
> > +     explicit constexpr operator bool() const
> > +     {
> > +             return *this != BaseDuration::zero();
> > +     }
> > +};
> > +
> >  } /* namespace utils */
> >
> > +#ifndef __DOXYGEN__
> > +template<class CharT, class Traits>
> > +static inline std::basic_ostream<CharT, Traits>
> &operator<<(std::basic_ostream<CharT, Traits> &os,
> > +                                                         const
> utils::Duration &d)
> > +{
> > +     std::basic_ostringstream<CharT, Traits> s;
> > +
> > +     s.flags(os.flags());
> > +     s.imbue(os.getloc());
> > +     s.setf(std::ios_base::fixed, std::ios_base::floatfield);
> > +     s.precision(2);
> > +     s << d.get<std::micro>() << "us";
> > +     return os << s.str();
> > +}
> > +#endif
> > +
> >  } /* namespace libcamera */
> >
> >  #endif /* __LIBCAMERA_INTERNAL_UTILS_H__ */
> > diff --git a/src/libcamera/utils.cpp b/src/libcamera/utils.cpp
> > index 826144d3c837..480284c6c2c9 100644
> > --- a/src/libcamera/utils.cpp
> > +++ b/src/libcamera/utils.cpp
> > @@ -506,6 +506,47 @@ std::string libcameraSourcePath()
> >   * loop, iterates over an indexed view of the \a iterable
> >   */
> >
> > +/**
> > + * \class Duration
> > + * \brief Helper class for std::chrono::duration types
>
> Helper class derived from std::chrono::duration that represents a time
> duration in nanoseconds with double precision
>

Ack.


>
> > + */
> > +
> > +/**
> > + * \typedef Duration::BaseDuration
> > + * \brief Base struct for the \a Duration helper class
> > + */
>
> Isn't this private ? does it need documentation ? It's just a
> syntactic sugar used in the class definition, isn't it ?
>

It is private/syntactic sugar - I was not sure what the rule was for
private members with regards to documentation.  I can remove
it.


>
>
> > +
> > +/**
> > + * \fn Duration::Duration(const std::chrono::duration<Rep, Period> &d)
> > + * \brief Copy constructor from a \a std::chrono::duration type
> > + * \param[in] d The std::chrono::duration object to convert from
> > + *
> > + * Constructs a \a Duration object from a \a std::chrono::duration
> object,
> > + * internally converting the representation to \a
> Duration::BaseDuration type
> > + */
> > +
> > +/**
> > + * \fn Duration::get<Period>()
> > + * \brief Retrieve the tick count, converted to the timebase provided
> by the
> > + * template argument Period of type \a std::ratio
> > + *
> > + * A typical usage example is given below:
> > + *
> > + * \code{.cpp}
> > + * utils::Duration d = 5s;
> > + * double d_in_ms = d.get<std::milli>();
> > + * \endcode
> > + *
> > + * \return The tick count of the Duration expressed in \a Period
> > + */
> > +
> > +/**
> > + * \fn Duration::operator bool()
> > + * \brief Boolean operator to test if a \a Duration holds a non-zero
> time value.
> > + *
> > + * \return True if \a Duration is a non-zero time value, False
> otherwise.
> > + */
>
> All minor, which if not other comments, can be changed with your ack
> when applying
> Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>
>

Thank's for the tag.  I will submit a v5 revision with the updates once you
and
others have a chance to comment on  all the other patches in the series.

Regards,
Naush


>
> Thanks
>   j
>
> > +
> >  } /* namespace utils */
> >
> >  } /* namespace libcamera */
> > --
> > 2.25.1
> >
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.libcamera.org/pipermail/libcamera-devel/attachments/20210524/9cb29a0c/attachment.htm>