[libcamera-devel] [PATCH v6 1/4] libcamera: utils: Add helper class for std::chrono::duration

[Laurent Pinchart]

Hi Naush,

Thank you for the patch.

On Tue, Jun 08, 2021 at 12:03:32PM +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 defined 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>
> Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  include/libcamera/internal/utils.h | 32 +++++++++++++++++
>  src/libcamera/utils.cpp            | 58 ++++++++++++++++++++++++++++++
>  test/utils.cpp                     | 45 +++++++++++++++++++++++
>  3 files changed, 135 insertions(+)
> 
> diff --git a/include/libcamera/internal/utils.h b/include/libcamera/internal/utils.h
> index 83dada7cc16c..15beb0f44172 100644
> --- a/include/libcamera/internal/utils.h
> +++ b/include/libcamera/internal/utils.h
> @@ -316,8 +316,40 @@ 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>
> +std::basic_ostream<CharT, Traits> &operator<<(std::basic_ostream<CharT, Traits> &os,
> +					      const utils::Duration &d);
> +#endif
> +
>  } /* namespace libcamera */
>  
>  #endif /* __LIBCAMERA_INTERNAL_UTILS_H__ */
> diff --git a/src/libcamera/utils.cpp b/src/libcamera/utils.cpp
> index 826144d3c837..2e7d35fb1173 100644
> --- a/src/libcamera/utils.cpp
> +++ b/src/libcamera/utils.cpp
> @@ -506,6 +506,64 @@ std::string libcameraSourcePath()
>   * loop, iterates over an indexed view of the \a iterable
>   */
>  
> +/**
> + * \class Duration
> + * \brief Helper class from std::chrono::duration that represents a time
> + * duration in nanoseconds with double precision
> + */
> +
> +/**
> + * \fn Duration::Duration(const std::chrono::duration<Rep, Period> &d)
> + * \brief Construct a Duration by converting an arbitrary std::chrono::duration
> + * \param[in] d The std::chrono::duration object to convert from
> + *
> + * The constructed \a Duration object is internally represented in double
> + * precision with nanoseconds ticks.
> + */
> +
> +/**
> + * \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
> + */
> +
>  } /* namespace utils */
>  
> +#ifndef __DOXYGEN__
> +template<class CharT, class Traits>
> +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();
> +}
> +
> +template
> +std::basic_ostream<char, std::char_traits<char>> &
> +operator<< <char, std::char_traits<char>>(std::basic_ostream<char, std::char_traits<char>> &os,
> +					  const utils::Duration &d);
> +#endif
> +
>  } /* namespace libcamera */
> diff --git a/test/utils.cpp b/test/utils.cpp
> index 7e24c71e4775..f170ae4c2f35 100644
> --- a/test/utils.cpp
> +++ b/test/utils.cpp
> @@ -20,6 +20,7 @@
>  
>  using namespace std;
>  using namespace libcamera;
> +using namespace std::literals::chrono_literals;
>  
>  class UtilsTest : public Test
>  {
> @@ -128,6 +129,46 @@ protected:
>  		return TestPass;
>  	}
>  
> +	int testDuration()
> +	{
> +		std::ostringstream os;
> +		utils::Duration exposure;
> +		double ratio;
> +
> +		exposure = 25ms + 25ms;
> +		if (exposure.get<std::micro>() != 50000.0) {
> +			cerr << "utils::Duration failed to return microsecond count";
> +			return TestFail;
> +		}
> +
> +		exposure = 1.0s / 4;
> +		if (exposure != 250ms) {
> +			cerr << "utils::Duration failed scalar divide test";
> +			return TestFail;
> +		}
> +
> +		exposure = 5000.5us;
> +		if (!exposure) {
> +			cerr << "utils::Duration failed boolean test";
> +			return TestFail;
> +		}
> +
> +		os << exposure;
> +		if (os.str() != "5000.50us") {
> +			cerr << "utils::Duration operator << failed";

I'll s/operator <</operator<</ and push the series after the tests
complete.

> +			return TestFail;
> +		}
> +
> +		exposure = 100ms;
> +		ratio = exposure / 25ms;
> +		if (ratio != 4.0) {
> +			cerr << "utils::Duration failed ratio test";
> +			return TestFail;
> +		}
> +
> +		return TestPass;
> +	}
> +
>  	int run()
>  	{
>  		/* utils::hex() test. */
> @@ -236,6 +277,10 @@ protected:
>  		if (testEnumerate() != TestPass)
>  			return TestFail;
>  
> +		/* utils::Duration test. */
> +		if (testDuration() != TestPass)
> +			return TestFail;
> +
>  		return TestPass;
>  	}
>  };

-- 
Regards,

Laurent Pinchart