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

[David Plowman]

Hi Naush

Thank you for this patch.

On Tue, 18 May 2021 at 11:09, Naushir Patuck <naush at raspberrypi.com> 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";

I suppose I wonder slightly why we change the precision, I assume the
output is just a bit tidier like that? And a space before the "us"? I
guess, why not!

Reviewed-by: David Plowman <david.plowman at raspberrypi.com>

Thanks
David

> +        os << std::setprecision(ss) << std::defaultfloat;
> +        return os;
> +}
> +
> +} // namespace RPiController
> --
> 2.25.1
>