/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <Kernel/Arch/i386/CPU.h>
#include <Kernel/Devices/RandomDevice.h>
#include <Kernel/Random.h>

namespace Kernel {

static u32 random32()
{
    if (g_cpu_supports_rdrand) {
        u32 value = 0;
        asm volatile(
            "1%=:\n"
            "rdrand %0\n"
            "jnc 1%=\n"
            : "=r"(value));
        return value;
    }
    // FIXME: This sucks lol
    static u32 next = 1;
    next = next * 1103515245 + 12345;
    return next;
}

void get_good_random_bytes(u8* buffer, size_t buffer_size)
{
    union {
        u8 bytes[4];
        u32 value;
    } u;
    size_t offset = 4;
    for (size_t i = 0; i < buffer_size; ++i) {
        if (offset >= 4) {
            u.value = random32();
            offset = 0;
        }
        buffer[i] = u.bytes[offset++];
    }
}

void get_fast_random_bytes(u8* buffer, size_t buffer_size)
{
    return get_good_random_bytes(buffer, buffer_size);
}

}