/* $Id: rand.cpp 890 2007-02-14 09:35:02Z vboxsync $ */
/** @file
 * InnoTek Portable Runtime - Random Number
 */

/*
 * Copyright (C) 2006 InnoTek Systemberatung GmbH
 *
 * This file is part of VirtualBox Open Source Edition (OSE), as
 * available from http://www.virtualbox.org. This file is free software;
 * you can redistribute it and/or modify it under the terms of the GNU
 * General Public License as published by the Free Software Foundation,
 * in version 2 as it comes in the "COPYING" file of the VirtualBox OSE
 * distribution. VirtualBox OSE is distributed in the hope that it will
 * be useful, but WITHOUT ANY WARRANTY of any kind.
 *
 * If you received this file as part of a commercial VirtualBox
 * distribution, then only the terms of your commercial VirtualBox
 * license agreement apply instead of the previous paragraph.
 */


/*******************************************************************************
*   Header Files                                                               *
*******************************************************************************/
#include <iprt/rand.h>
#include <iprt/time.h>
#include <iprt/asm.h>
#include <iprt/err.h>
#include <iprt/assert.h>
#include <iprt/thread.h>
#include "internal/rand.h"


/*******************************************************************************
*   Global Variables                                                           *
*******************************************************************************/
/** Lazy init. */
static volatile bool    g_fInitialized = false;
/** The context variable for the fallback path. */
static uint32_t         g_u32Ctx;


/*******************************************************************************
*   Internal Functions                                                         *
*******************************************************************************/
static uint32_t rtRandGenBytesFallbackU31(uint32_t *pCtx);


/**
 * Lazy initialization of the native and fallback random byte sources.
 * 
 */
static void rtRandLazyInit(void)
{
    /*
     * Seed the fallback random code.
     */
    g_u32Ctx = (uint32_t)(ASMReadTSC() >> 8);

    /*
     * Call host specific init.
     */
    rtRandLazyInitNative();
    g_fInitialized = true;
}


/**
 * Internal wrapper for the native and generic random byte methods.
 *
 * @param   pv  Where to store the random bytes.
 * @param   cb  Number of bytes to generate.
 */
static void rtRandGenBytes(void *pv, size_t cb)
{
    Assert(cb);
    if (RT_UNLIKELY(!g_fInitialized))
        rtRandLazyInit();

    int rc = rtRandGenBytesNative(pv, cb);
    if (RT_FAILURE(rc))
        rtRandGenBytesFallback(pv, cb);
}


/**
 * Fills a buffer with random bytes.
 *
 * @param   pv  Where to store the random bytes.
 * @param   cb  Number of bytes to generate.
 */
RTDECL(void) RTRandBytes(void *pv, size_t cb)
{
    if (cb)
        rtRandGenBytes(pv, cb);
}


/**
 * Generate a 32-bit signed random number in the set [i32First..i32Last].
 * 
 * @returns The random number.
 * @param   i32First    First number in the set.
 * @param   i32Last     Last number in the set.
 */
RTDECL(int32_t) RTRandS32Ex(int32_t i32First, int32_t i32Last)
{
    /* get 4 random bytes. */
    union
    {
        uint32_t    off;
        uint8_t     ab[4];
    } u;
    rtRandGenBytes(&u.ab, sizeof(u));


    /* squeeze it into the requested range. */
    uint32_t offLast = i32Last - i32First;
    if (u.off > offLast)
    {
        do
        {
            u.off >>= 1;
        } while (u.off > offLast);
    }
    return i32First + u.off;
}


/**
 * Generate a 32-bit signed random number.
 * 
 * @returns The random number.
 */
RTDECL(int32_t) RTRandS32(void)
{
    return RTRandS32Ex(INT32_MIN, INT32_MAX);
}


/**
 * Generate a 32-bit unsigned random number in the set [u32First..u32Last].
 * 
 * @returns The random number.
 * @param   u32First    First number in the set.
 * @param   u32Last     Last number in the set.
 */
RTDECL(uint32_t) RTRandU32Ex(uint32_t u32First, uint32_t u32Last)
{
    /* get 4 random bytes. */
    union
    {
        uint32_t    off;
        uint8_t     ab[4];
    } u;
    rtRandGenBytes(&u.ab, sizeof(u));


    /* squeeze it into the requested range. */
    const uint32_t offLast = u32Last - u32First;
    if (u.off > offLast)
    {
        do
        {
            u.off >>= 1;
        } while (u.off > offLast);
    }
    return u32First + u.off;
}


/**
 * Generate a 32-bit unsigned random number.
 * 
 * @returns The random number.
 */
RTDECL(uint32_t) RTRandU32(void)
{
    return RTRandU32Ex(0, UINT32_MAX);
}


/**
 * Generate a 32-bit signed random number in the set [i32First..i32Last].
 * 
 * @returns The random number.
 * @param   i32First    First number in the set.
 * @param   i32Last     Last number in the set.
 */
RTDECL(int64_t) RTRandS64Ex(int64_t i64First, int64_t i64Last)
{
    /* get 8 random bytes. */
    union
    {
        uint64_t    off;
        uint8_t     ab[8];
    } u;
    rtRandGenBytes(&u.ab, sizeof(u));

    /* squeeze it into the requested range. */
    uint64_t offLast = i64Last - i64First;
    if (u.off > offLast)
    {
        do
        {
            u.off >>= 1;
        } while (u.off > offLast);
    }
    return i64First + u.off;
}


/**
 * Generate a 64-bit signed random number.
 * 
 * @returns The random number.
 */
RTDECL(int64_t) RTRandS64(void)
{
    return RTRandS64Ex(INT64_MIN, INT64_MAX);
}


/**
 * Generate a 64-bit unsigned random number in the set [u64First..u64Last].
 * 
 * @returns The random number.
 * @param   u64First    First number in the set.
 * @param   u64Last     Last number in the set.
 */
RTDECL(uint64_t) RTRandU64Ex(uint64_t u64First, uint64_t u64Last)
{
    /* get 8 random bytes. */
    union
    {
        uint64_t    off;
        uint8_t     ab[8];
    } u;
    rtRandGenBytes(&u.ab, sizeof(u));

    /* squeeze it into the requested range. */
    const uint64_t offLast = u64Last - u64First;
    if (u.off > offLast)
    {
        do
        {
            u.off >>= 1;
        } while (u.off > offLast);
    }
    return u64First + u.off;
}


/**
 * Generate a 64-bit unsigned random number.
 * 
 * @returns The random number.
 */
RTDECL(uint64_t) RTRandU64(void)
{
    return RTRandU64Ex(0, UINT64_MAX);
}


/**
 * Fallback random byte source.
 *
 * @param   pv  Where to store the random bytes.
 * @param   cb  Number of bytes to generate.
 */
void rtRandGenBytesFallback(void *pv, size_t cb)
{
    uint8_t *pb = (uint8_t *)pv;
    for (unsigned i = 0;; i++)
    {
        uint32_t u32 = rtRandGenBytesFallbackU31(&g_u32Ctx);

        *pb++ = (uint8_t)u32;
        if (!--cb)
            break;

        u32 >>= 8;
        *pb++ = (uint8_t)u32;
        if (!--cb)
            break;

        u32 >>= 8;
        *pb++ = (uint8_t)u32;
        if (!--cb)
            break;

        /* Is this really a good idea? */
        if (!(i % 3))
        {
            if (i)
                RTThreadYield();
            *pb++ = (uint8_t)ASMReadTSC();
            if (!--cb)
                break;
        }
    }

}


/*-
 * Copyright (c) 1990, 1993
 *	The Regents of the University of California.  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.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 */

/* The core of:
__FBSDID("$FreeBSD: /repoman/r/ncvs/src/lib/libc/stdlib/rand.c,v 1.16 2007/01/09 00:28:10 imp Exp $");
*/

/**
 * Generates an unsigned 31 bit pseudo random number.
 * 
 * @returns pseudo random number.
 * @param   pCtx    The context.
 */
static uint32_t rtRandGenBytesFallbackU31(uint32_t *pCtx)
{
    /*
     * Compute x = (7^5 * x) mod (2^31 - 1)
     * without overflowing 31 bits:
     *      (2^31 - 1) = 127773 * (7^5) + 2836
     *
     * From "Random number generators: good ones are hard to find",  Park and 
     * Miller, Communications of the ACM, vol. 31, no. 10, October 1988, p. 1195.
     */
    uint32_t Ctx = *pCtx;
    if (!Ctx) /* must not be zero. */
        Ctx = 0x20070212;
    uint32_t Hi = Ctx / 127773;
    uint32_t Lo = Ctx % 127773;
    int32_t x = 16807 * Lo  -  2836 * Hi;
    if (x < 0)
        x += INT32_MAX;
    *pCtx = x;
    return x % INT32_MAX;
}