Source/WTF/wtf/GenericTimeMixin.h

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 * Copyright (C) 2021 Apple Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 * 1. Redistributions of source code must retain the above copyright
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 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
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#pragma once

#include <wtf/Seconds.h>

namespace WTF {

template<typename DerivedTime>
class GenericTimeMixin {
    WTF_MAKE_FAST_ALLOCATED;
public:
    // Call this if you know for sure that the double represents the time according to the
    // same time source as DerivedTime. It must be in seconds.
    static constexpr DerivedTime fromRawSeconds(double value)
    {
        return DerivedTime(value);
    }

    static constexpr DerivedTime infinity() { return fromRawSeconds(std::numeric_limits<double>::infinity()); }
    static constexpr DerivedTime nan() { return fromRawSeconds(std::numeric_limits<double>::quiet_NaN()); }

    constexpr Seconds secondsSinceEpoch() const { return Seconds(m_value); }

    explicit constexpr operator bool() const { return !!m_value; }

    constexpr DerivedTime operator+(Seconds other) const
    {
        return fromRawSeconds(m_value + other.value());
    }

    constexpr DerivedTime operator-(Seconds other) const
    {
        return fromRawSeconds(m_value - other.value());
    }

    Seconds operator%(Seconds other) const
    {
        return Seconds { fmod(m_value, other.value()) };
    }

    // Time is a scalar and scalars can be negated as this could arise from algebraic
    // transformations. So, we allow it.
    constexpr DerivedTime operator-() const
    {
        return fromRawSeconds(-m_value);
    }

    DerivedTime operator+=(Seconds other)
    {
        return *static_cast<DerivedTime*>(this) = *static_cast<DerivedTime*>(this) + other;
    }

    DerivedTime operator-=(Seconds other)
    {
        return *static_cast<DerivedTime*>(this) = *static_cast<DerivedTime*>(this) - other;
    }

    constexpr Seconds operator-(DerivedTime other) const
    {
        return Seconds(m_value - other.m_value);
    }

    constexpr bool operator==(DerivedTime other) const
    {
        return m_value == other.m_value;
    }

    constexpr bool operator!=(DerivedTime other) const
    {
        return m_value != other.m_value;
    }

    constexpr bool operator<(DerivedTime other) const
    {
        return m_value < other.m_value;
    }

    constexpr bool operator>(DerivedTime other) const
    {
        return m_value > other.m_value;
    }

    constexpr bool operator<=(DerivedTime other) const
    {
        return m_value <= other.m_value;
    }

    constexpr bool operator>=(DerivedTime other) const
    {
        return m_value >= other.m_value;
    }

    DerivedTime isolatedCopy() const
    {
        return *static_cast<const DerivedTime*>(this);
    }

    template<class Encoder>
    void encode(Encoder& encoder) const
    {
        encoder << m_value;
    }

    template<class Decoder>
    static std::optional<DerivedTime> decode(Decoder& decoder)
    {
        std::optional<double> time;
        decoder >> time;
        if (!time)
            return std::nullopt;
        return DerivedTime::fromRawSeconds(*time);
    }

    template<class Decoder>
    static WARN_UNUSED_RETURN bool decode(Decoder& decoder, DerivedTime& time)
    {
        double value;
        if (!decoder.decode(value))
            return false;

        time = DerivedTime::fromRawSeconds(value);
        return true;
    }

protected:
    // This is the epoch. So, x.secondsSinceEpoch() should be the same as x - DerivedTime().
    constexpr GenericTimeMixin() = default;

    constexpr GenericTimeMixin(double rawValue)
        : m_value(rawValue)
    {
    }

    double m_value { 0 };
};

} // namespace WTF