ladybird/Libraries/LibWeb/HTML/NavigatorDeviceMemory.h

/*
 * Copyright (c) 2024, Jelle Raaijmakers <jelle@ladybird.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include <AK/BuiltinWrappers.h>
#include <LibCore/System.h>
#include <LibWeb/WebIDL/Types.h>

namespace Web::HTML {

class NavigatorDeviceMemoryMixin {
public:
    // https://www.w3.org/TR/device-memory/#computing-device-memory-value
    WebIDL::Double device_memory() const
    {
        // The value is calculated by using the actual device memory in MiB then rounding it to the
        // nearest number where only the most signicant bit can be set and the rest are zeros
        // (nearest power of two).
        auto memory_in_bytes = Core::System::physical_memory_bytes();
        auto memory_in_mib = memory_in_bytes / MiB;
        auto required_bits = AK::count_required_bits(memory_in_mib);
        auto lower_memory_in_mib = static_cast<u64>(1) << (required_bits - 1);
        auto upper_memory_in_mib = static_cast<u64>(1) << required_bits;
        auto rounded_memory_in_mib = upper_memory_in_mib - memory_in_mib <= memory_in_mib - lower_memory_in_mib
            ? upper_memory_in_mib
            : lower_memory_in_mib;

        // Then dividing that number by 1024.0 to get the value in GiB.
        auto memory_in_gib = static_cast<WebIDL::Double>(rounded_memory_in_mib) / 1024.0;

        // An upper bound and a lower bound should be set on the list of values.
        return AK::clamp(memory_in_gib, 1.0, 4.0);
    }
};

}