ladybird/AK/Endian.h

/*
 * Copyright (c) 2020, the SerenityOS developers.
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include <AK/Format.h>
#include <AK/Forward.h>
#include <AK/Platform.h>

namespace AK {

#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
inline constexpr static bool HostIsLittleEndian = true;
#else
inline constexpr static bool HostIsLittleEndian = false;
#endif

enum class Endianness {
    Host,
    Big,
    Little,
};

template<typename T>
ALWAYS_INLINE constexpr T convert_between_host_and_little_endian(T value)
{
    if constexpr (HostIsLittleEndian || sizeof(T) == 1)
        return value;
    else if constexpr (sizeof(T) == 8)
        return static_cast<T>(__builtin_bswap64(static_cast<u64>(value)));
    else if constexpr (sizeof(T) == 4)
        return static_cast<T>(__builtin_bswap32(static_cast<u32>(value)));
    else if constexpr (sizeof(T) == 2)
        return static_cast<T>(__builtin_bswap16(static_cast<u16>(value)));
    else
        static_assert(DependentFalse<T>, "Cannot byte-swap values larger than 64-bits");
}

template<typename T>
ALWAYS_INLINE constexpr T convert_between_host_and_big_endian(T value)
{
    if constexpr (sizeof(T) == 1 || !HostIsLittleEndian)
        return value;
    else if constexpr (sizeof(T) == 8)
        return static_cast<T>(__builtin_bswap64(static_cast<u64>(value)));
    else if constexpr (sizeof(T) == 4)
        return static_cast<T>(__builtin_bswap32(static_cast<u32>(value)));
    else if constexpr (sizeof(T) == 2)
        return static_cast<T>(__builtin_bswap16(static_cast<u16>(value)));
    else
        static_assert(DependentFalse<T>, "Cannot byte-swap values larger than 64-bits");
}

template<typename T>
ALWAYS_INLINE T convert_between_host_and_network_endian(T value)
{
    return convert_between_host_and_big_endian(value);
}

template<typename T>
class [[gnu::packed]] LittleEndian {
public:
    constexpr LittleEndian() = default;

    constexpr LittleEndian(T value)
        : m_value(convert_between_host_and_little_endian(value))
    {
    }

    constexpr operator T() const { return convert_between_host_and_little_endian(m_value); }

private:
    T m_value { 0 };
};

template<typename T>
class [[gnu::packed]] BigEndian {
public:
    constexpr BigEndian() = default;

    constexpr BigEndian(T value)
        : m_value(convert_between_host_and_big_endian(value))
    {
    }

    constexpr operator T() const { return convert_between_host_and_big_endian(m_value); }

private:
    T m_value { 0 };
};

template<typename T>
using NetworkOrdered = BigEndian<T>;

template<typename T>
requires(HasFormatter<T>) struct Formatter<LittleEndian<T>> : Formatter<T> {
};

template<typename T>
requires(HasFormatter<T>) struct Formatter<BigEndian<T>> : Formatter<T> {
};

template<typename T>
struct Traits<LittleEndian<T>> : public DefaultTraits<LittleEndian<T>> {
    static constexpr bool is_trivially_serializable() { return Traits<T>::is_trivially_serializable(); }
};

template<typename T>
struct Traits<BigEndian<T>> : public DefaultTraits<BigEndian<T>> {
    static constexpr bool is_trivially_serializable() { return Traits<T>::is_trivially_serializable(); }
};

constexpr u16 bitswap(u16 v)
{
    v = ((v >> 1) & 0x5555) | ((v & 0x5555) << 1);    // even & odd bits
    v = ((v >> 2) & 0x3333) | ((v & 0x3333) << 2);    // pairs
    v = ((v >> 4) & 0x0F0F) | ((v & 0x0F0F) << 4);    // nibbles
    return ((v >> 8) & 0x00FF) | ((v & 0x00FF) << 8); // bytes
}

}

#if USING_AK_GLOBALLY
using AK::BigEndian;
using AK::bitswap;
using AK::LittleEndian;
using AK::NetworkOrdered;
#endif