ladybird/AK/Random.h

/*
 * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include <AK/Platform.h>
#include <AK/StdLibExtras.h>
#include <AK/Types.h>

#if defined(AK_OS_SERENITY) || defined(AK_OS_ANDROID)
#    include <stdlib.h>
#endif

#if defined(__unix__)
#    include <unistd.h>
#endif

#if defined(AK_OS_MACOS)
#    include <sys/random.h>
#endif

#if defined(AK_OS_WINDOWS)
#    include <stdlib.h>
#endif

namespace AK {

inline void fill_with_random([[maybe_unused]] void* buffer, [[maybe_unused]] size_t length)
{
#if defined(AK_OS_SERENITY) || defined(AK_OS_ANDROID)
    arc4random_buf(buffer, length);
#elif defined(OSS_FUZZ)
#elif defined(__unix__) or defined(AK_OS_MACOS)
    [[maybe_unused]] int rc = getentropy(buffer, length);
#else
    char* char_buffer = static_cast<char*>(buffer);
    for (size_t i = 0; i < length; i++) {
        char_buffer[i] = rand();
    }
#endif
}

template<typename T>
inline T get_random()
{
    T t;
    fill_with_random(&t, sizeof(T));
    return t;
}

u32 get_random_uniform(u32 max_bounds);

template<typename Collection>
inline void shuffle(Collection& collection)
{
    // Fisher-Yates shuffle
    for (size_t i = collection.size() - 1; i >= 1; --i) {
        size_t j = get_random_uniform(i + 1);
        AK::swap(collection[i], collection[j]);
    }
}

// shuffle() implementation for NonnullPtrVector, since its operator[] returns a reference to the pointed-at value
// instead of the pointer itself.
template<typename Collection>
requires(requires(Collection collection) { collection.ptr_at(0); })
inline void shuffle(Collection& collection)
{
    // Fisher-Yates shuffle
    for (size_t i = collection.size() - 1; i >= 1; --i) {
        size_t j = get_random_uniform(i + 1);
        AK::swap(collection.ptr_at(i), collection.ptr_at(j));
    }
}

}

#if USING_AK_GLOBALLY
using AK::fill_with_random;
using AK::get_random;
using AK::get_random_uniform;
using AK::shuffle;
#endif