[libcamera-devel] [PATCH v2 1/5] libcamera: flags: Add type-safe enum-based flags
Jacopo Mondi
jacopo at jmondi.org
Mon Jul 26 11:42:23 CEST 2021
Hi Laurent
On Sun, Jul 25, 2021 at 08:18:23PM +0300, Laurent Pinchart wrote:
> Add a Flags template class that provide type-safe bitwise operators on
> enum values. This allows using enum types for bit fields, without giving
> away type-safety as usually done when storing combined flags in integer
> variables.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> Reviewed-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
> ---
> include/libcamera/base/flags.h | 195 +++++++++++++++++++++++++++++
> include/libcamera/base/meson.build | 1 +
> src/libcamera/base/flags.cpp | 192 ++++++++++++++++++++++++++++
> src/libcamera/base/meson.build | 1 +
> 4 files changed, 389 insertions(+)
> create mode 100644 include/libcamera/base/flags.h
> create mode 100644 src/libcamera/base/flags.cpp
>
> diff --git a/include/libcamera/base/flags.h b/include/libcamera/base/flags.h
> new file mode 100644
> index 000000000000..adec549dccc9
> --- /dev/null
> +++ b/include/libcamera/base/flags.h
> @@ -0,0 +1,195 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2020, Google Inc.
> + *
> + * flags.h - Type-safe enum-based bitfields
> + */
> +#ifndef __LIBCAMERA_BASE_FLAGS_H__
> +#define __LIBCAMERA_BASE_FLAGS_H__
> +
> +#include <type_traits>
> +
> +namespace libcamera {
> +
> +template<typename E>
> +class Flags
> +{
> +public:
> + static_assert(std::is_enum<E>::value,
> + "Flags<> template parameter must be an enum");
> +
> + using Type = std::underlying_type_t<E>;
> +
> + constexpr Flags()
> + : value_(0)
> + {
> + }
> +
> + constexpr Flags(E flag)
> + : value_(static_cast<Type>(flag))
> + {
> + }
> +
> + constexpr Flags &operator&=(E flag)
> + {
> + value_ &= static_cast<Type>(flag);
> + return *this;
> + }
> +
> + constexpr Flags &operator&=(Flags other)
Should other be const ?
> + {
> + value_ &= other.value_;
> + return *this;
> + }
> +
> + constexpr Flags &operator|=(E flag)
> + {
> + value_ |= static_cast<Type>(flag);
> + return *this;
> + }
> +
> + constexpr Flags &operator|=(Flags other)
> + {
> + value_ |= other.value_;
> + return *this;
> + }
> +
> + constexpr Flags &operator^=(E flag)
> + {
> + value_ ^= static_cast<Type>(flag);
> + return *this;
> + }
> +
> + constexpr Flags &operator^=(Flags other)
> + {
> + value_ ^= other.value_;
> + return *this;
> + }
> +
> + constexpr bool operator==(E flag)
> + {
> + return value_ == static_cast<Type>(flag);
> + }
> +
> + constexpr bool operator==(Flags other)
> + {
> + return value_ == static_cast<Type>(other);
> + }
> +
> + constexpr bool operator!=(E flag)
> + {
> + return value_ != static_cast<Type>(flag);
> + }
> +
> + constexpr bool operator!=(Flags other)
> + {
> + return value_ != static_cast<Type>(other);
> + }
> +
> + constexpr explicit operator Type() const
> + {
> + return value_;
> + }
> +
> + constexpr explicit operator bool() const
> + {
> + return !!value_;
> + }
> +
> + constexpr Flags operator&(E flag) const
> + {
> + return Flags(static_cast<E>(value_ & static_cast<Type>(flag)));
> + }
> +
> + constexpr Flags operator&(Flags other) const
> + {
> + return Flags(static_cast<E>(value_ & other.value_));
> + }
> +
> + constexpr Flags operator|(E flag) const
> + {
> + return Flags(static_cast<E>(value_ | static_cast<Type>(flag)));
> + }
> +
> + constexpr Flags operator|(Flags other) const
> + {
> + return Flags(static_cast<E>(value_ | other.value_));
> + }
> +
> + constexpr Flags operator^(E flag) const
> + {
> + return Flags(static_cast<E>(value_ ^ static_cast<Type>(flag)));
> + }
> +
> + constexpr Flags operator^(Flags other) const
> + {
> + return Flags(static_cast<E>(value_ ^ other.value_));
> + }
> +
> + constexpr Flags operator~() const
> + {
> + return Flags(static_cast<E>(~value_));
> + }
> +
> + constexpr bool operator!() const
> + {
> + return !value_;
> + }
> +
> +private:
> + Type value_;
> +};
> +
> +#ifndef __DOXYGEN__
> +template<typename E>
> +struct flags_enable_operators {
> + static const bool enable = false;
> +};
> +
> +template<typename E>
> +typename std::enable_if_t<flags_enable_operators<E>::enable, Flags<E>>
> +operator|(E lhs, E rhs)
> +{
> + using type = std::underlying_type_t<E>;
> + return Flags<E>(static_cast<E>(static_cast<type>(lhs) | static_cast<type>(rhs)));
> +}
> +
> +template<typename E>
> +typename std::enable_if_t<flags_enable_operators<E>::enable, Flags<E>>
> +operator&(E lhs, E rhs)
> +{
> + using type = std::underlying_type_t<E>;
> + return Flags<E>(static_cast<E>(static_cast<type>(lhs) & static_cast<type>(rhs)));
> +}
> +
> +template<typename E>
> +typename std::enable_if_t<flags_enable_operators<E>::enable, Flags<E>>
> +operator^(E lhs, E rhs)
> +{
> + using type = std::underlying_type_t<E>;
> + return Flags<E>(static_cast<E>(static_cast<type>(lhs) ^ static_cast<type>(rhs)));
> +}
> +
> +template<typename E>
> +typename std::enable_if_t<flags_enable_operators<E>::enable, Flags<E>>
> +operator~(E rhs)
> +{
> + using type = std::underlying_type_t<E>;
> + return Flags<E>(static_cast<E>(~static_cast<type>(rhs)));
> +}
> +
> +#define LIBCAMERA_FLAGS_ENABLE_OPERATORS(_enum) \
> +template<> \
> +struct flags_enable_operators<_enum> { \
> + static const bool enable = true; \
> +};
> +
> +#else /* __DOXYGEN__ */
> +
> +#define LIBCAMERA_FLAGS_ENABLE_OPERATORS(_enum)
> +
> +#endif /* __DOXYGEN__ */
> +
> +} /* namespace libcamera */
> +
> +#endif /* __LIBCAMERA_BASE_FLAGS_H__ */
> diff --git a/include/libcamera/base/meson.build b/include/libcamera/base/meson.build
> index 7c499b558fb0..9feb4b9346d5 100644
> --- a/include/libcamera/base/meson.build
> +++ b/include/libcamera/base/meson.build
> @@ -9,6 +9,7 @@ libcamera_base_headers = files([
> 'event_dispatcher_poll.h',
> 'event_notifier.h',
> 'file.h',
> + 'flags.h',
> 'log.h',
> 'message.h',
> 'object.h',
> diff --git a/src/libcamera/base/flags.cpp b/src/libcamera/base/flags.cpp
> new file mode 100644
> index 000000000000..3e4320ace7c8
> --- /dev/null
> +++ b/src/libcamera/base/flags.cpp
> @@ -0,0 +1,192 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2020, Google Inc.
> + *
> + * flags.cpp - Type-safe enum-based bitfields
> + */
> +
> +#include <libcamera/base/flags.h>
> +
> +/**
> + * \file base/flags.h
> + * \brief Enum-based bit fields
> + */
> +
> +namespace libcamera {
> +
> +/**
> + * \class Flags
> + * \brief Type-safe container for enum-based bitfields
> + *
> + * The Flags template class provides type-safe bitwise operators on enum values.
> + * It allows using enum types for bitfields, while preventing unsafe casts from
> + * integer types and mixing of flags from different enum types.
> + *
> + * To use the Flags class, declare an enum containing the desired bit flags, and
> + * use the Flags<enum> class to store bitfields based on the enum. If bitwise
> + * operators on the underlying enum are also desired, they can be enabled with
> + * the LIBCAMERA_FLAGS_ENABLE_OPERATORS(enum) macro.
> + */
> +
> +/**
> + * \typedef Flags::Type
> + * \brief The underlying data type of the enum
> + */
> +
> +/**
> + * \fn Flags::Flags()
> + * \brief Construct a Flags instance with a zero value
> + */
> +
> +/**
> + * \fn Flags::Flags(E flag)
> + * \brief Construct a Flags instance storing the \a flag
> + * \param[in] flag The initial value
> + */
> +
> +/**
> + * \fn Flags &Flags::operator&=(E flag)
> + * \brief Store the bitwise AND of this Flags and the \a flag in this Flags
> + * \param[in] flag The second operand
> + * \return A reference to this Flags
> + */
> +
> +/**
> + * \fn Flags &Flags::operator&=(Flags other)
> + * \brief Store the bitwise AND of this Flags and the \a other Flags in this Flags
> + * \param[in] other The second operand
> + * \return A reference to this Flags
> + */
> +
> +/**
> + * \fn Flags &Flags::operator|=(E flag)
> + * \brief Store the bitwise OR of this Flags and the \a flag in this Flags
> + * \param[in] flag The second operand
> + * \return A reference to this Flags
> + */
> +
> +/**
> + * \fn Flags &Flags::operator|=(Flags other)
> + * \brief Store the bitwise OR of this Flags and the \a other Flags in this Flags
> + * \param[in] other The second operand
> + * \return A reference to this Flags
> + */
> +
> +/**
> + * \fn Flags &Flags::operator^=(E flag)
> + * \brief Store the bitwise XOR of this Flags and the \a flag in this Flags
> + * \param[in] flag The second operand
> + * \return A reference to this Flags
> + */
> +
> +/**
> + * \fn Flags &Flags::operator^=(Flags other)
> + * \brief Store the bitwise XOR of this Flags and the \a other Flags in this Flags
> + * \param[in] other The second operand
> + * \return A reference to this Flags
> + */
> +
> +/**
> + * \fn bool Flags::operator==(E flag)
> + * \brief Compare flags for equality
> + * \param[in] flag The second operand
> + * \return True if the Flags and \a flag are equal, false otherwise
> + */
> +
> +/**
> + * \fn bool Flags::operator==(Flags other)
> + * \brief Compare flags for equality
> + * \param[in] other The second operand
> + * \return True if the Flags and \a other are equal, false otherwise
> + */
> +
> +/**
> + * \fn bool Flags::operator!=(E flag)
> + * \brief Compare flags for non-equality
> + * \param[in] flag The second operand
> + * \return True if the Flags and \a flag are not equal, false otherwise
> + */
> +
> +/**
> + * \fn bool Flags::operator!=(Flags other)
> + * \brief Compare flags for non-equality
> + * \param[in] other The second operand
> + * \return True if the Flags and \a other are not equal, false otherwise
> + */
> +
> +/**
> + * \fn Flags::operator Type() const
> + * \brief Convert the Flags to the underlying integer type
> + * \return The Flags value as an integer
> + */
> +
> +/**
> + * \fn Flags::operator bool() const
> + * \brief Convert the Flags to a boolean
> + * \return True if at least one flag is set, false otherwise
> + */
> +
> +/**
> + * \fn Flags Flags::operator&(E flag) const
> + * \brief Compute the bitwise AND of this Flags and the \a flag
> + * \param[in] flag The second operand
> + * \return A Flags containing the result of the AND operation
> + */
> +
> +/**
> + * \fn Flags Flags::operator&(Flags other) const
> + * \brief Compute the bitwise AND of this Flags and the \a other Flags
> + * \param[in] other The second operand
> + * \return A Flags containing the result of the AND operation
> + */
> +
> +/**
> + * \fn Flags Flags::operator|(E flag) const
> + * \brief Compute the bitwise OR of this Flags and the \a flag
> + * \param[in] flag The second operand
> + * \return A Flags containing the result of the OR operation
> + */
> +
> +/**
> + * \fn Flags Flags::operator|(Flags other) const
> + * \brief Compute the bitwise OR of this Flags and the \a other Flags
> + * \param[in] other The second operand
> + * \return A Flags containing the result of the OR operation
> + */
> +
> +/**
> + * \fn Flags Flags::operator^(E flag) const
> + * \brief Compute the bitwise XOR of this Flags and the \a flag
> + * \param[in] flag The second operand
> + * \return A Flags containing the result of the XOR operation
> + */
> +
> +/**
> + * \fn Flags Flags::operator^(Flags other) const
> + * \brief Compute the bitwise XOR of this Flags and the \a other Flags
> + * \param[in] other The second operand
> + * \return A Flags containing the result of the XOR operation
> + */
> +
> +/**
> + * \fn Flags Flags::operator~() const
> + * \brief Compute the bitwise NOT of this Flags
> + * \return A Flags containing the result of the NOT operation
> + */
> +
> +/**
> + * \fn bool Flags::operator!() const
> + * \brief Check if flags are set
> + * \return True if no flags is set, false otherwise
> + */
> +
> +/**
> + * \def LIBCAMERA_FLAGS_ENABLE_OPERATORS(enum)
> + * \brief Enable bitwise operations on the \a enum enumeration
> + *
> + * This macro enables the bitwise AND, OR, XOR and NOT operators on the given
> + * \a enum. This allows the enum values to be safely used in bitwise operations
> + * with the Flags<> class.
> + */
> +
> +} /* namespace libcamera */
> diff --git a/src/libcamera/base/meson.build b/src/libcamera/base/meson.build
> index 871721571e98..d799c66d8b3a 100644
> --- a/src/libcamera/base/meson.build
> +++ b/src/libcamera/base/meson.build
> @@ -7,6 +7,7 @@ libcamera_base_sources = files([
> 'event_dispatcher_poll.cpp',
> 'event_notifier.cpp',
> 'file.cpp',
> + 'flags.cpp',
> 'log.cpp',
> 'message.cpp',
> 'object.cpp',
Great!
Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>
Thanks
j
> --
> Regards,
>
> Laurent Pinchart
>
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