[libcamera-devel] [PATCH 1/4] ipa: raspberrypi: Add helper macros for std::chrono::duration

[Laurent Pinchart]

Hi Naush,

Thank you for the patch.

On Tue, May 18, 2021 at 11:07:03AM +0100, Naushir Patuck wrote:
> A new RPiController::Duration typedef is defined to represent a
> std::chrono::duration type with double precision nanosecond timebase
> that will be used throughout. This minimises the loss of precision when
> converting timebases. A function for returning the duration count in any
> timebase is also provided.
> 
> An operator << overload is define to help with displaying
> RPiController::Duration value in stream objects.
> 
> Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> ---
>  src/ipa/raspberrypi/controller/duration.hpp | 33 +++++++++++++++++++++
>  1 file changed, 33 insertions(+)
>  create mode 100644 src/ipa/raspberrypi/controller/duration.hpp
> 
> diff --git a/src/ipa/raspberrypi/controller/duration.hpp b/src/ipa/raspberrypi/controller/duration.hpp
> new file mode 100644
> index 000000000000..98aa3d78f52f
> --- /dev/null
> +++ b/src/ipa/raspberrypi/controller/duration.hpp
> @@ -0,0 +1,33 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */
> +/*
> + * Copyright (C) 2021, Raspberry Pi (Trading) Limited
> + *
> + * duration.hpp - Helper macros for std::chrono::duration handling.
> + */
> +#pragma once
> +
> +#include <chrono>
> +#include <iomanip>
> +#include <iostream>
> +
> +namespace RPiController {
> +
> +using Duration = std::chrono::duration<double, std::nano>;
> +
> +// Helper to convert and return the count of any std::chrono::duration type to
> +// another timebase.  Use a double rep type to try and preserve precision.
> +template <typename P, typename T>
> +static constexpr double DurationValue(T const &d)
> +{
> +	return std::chrono::duration_cast<std::chrono::duration<double, P>>(d).count();
> +};
> +
> +static inline std::ostream &operator<<(std::ostream &os, const Duration &duration)
> +{
> +        std::streamsize ss = os.precision();
> +        os << std::fixed << std::setprecision(2) << DurationValue<std::micro>(duration) << " us";
> +        os << std::setprecision(ss) << std::defaultfloat;

This will reset to std::defaultfloat, while the stream may already be in
std::fixed.

> +        return os;
> +}

Would it be too much yak-shaving to ask for the implementation to be
closer to
https://en.cppreference.com/w/cpp/chrono/duration/operator_ltlt, and
moved to utils.h ? It could be useful more widely in libcamera than just
in the RPi IPA.

> +
> +} // namespace RPiController

-- 
Regards,

Laurent Pinchart