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/* $Id: randparkmiller.cpp $ */
/** @file
* IPRT - Random Numbers, Park-Miller Pseudo Random.
*/
/*
* Copyright (C) 2008-2023 Oracle and/or its affiliates.
*
* This file is part of VirtualBox base platform packages, as
* available from https://www.virtualbox.org.
*
* This program 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 3 of the
* License.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <https://www.gnu.org/licenses>.
*
* The contents of this file may alternatively be used under the terms
* of the Common Development and Distribution License Version 1.0
* (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
* in the VirtualBox distribution, in which case the provisions of the
* CDDL are applicable instead of those of the GPL.
*
* You may elect to license modified versions of this file under the
* terms and conditions of either the GPL or the CDDL or both.
*
* SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
*/
/*********************************************************************************************************************************
* Header Files *
*********************************************************************************************************************************/
#include <iprt/rand.h>
#include "internal/iprt.h"
#include <iprt/asm-math.h>
#include <iprt/mem.h>
#include <iprt/string.h>
#include <iprt/errcore.h>
#include "internal/rand.h"
#include "internal/magics.h"
DECLINLINE(uint32_t) rtRandParkMillerU31(uint32_t *pu32Ctx)
{
/*
* Park-Miller random number generator:
* X2 = X1 * g mod n.
*
* We use the constants suggested by Park and Miller:
* n = 2^31 - 1 = INT32_MAX
* g = 7^5 = 16807
*
* This will produce numbers in the range [0..INT32_MAX-1], which is
* almost 31-bits. We'll ignore the missing number for now and settle
* for just filling in the missing bit instead (the caller does this).
*/
uint32_t x1 = *pu32Ctx;
if (!x1)
x1 = 20080806;
/*uint32_t x2 = ((uint64_t)x1 * 16807) % INT32_MAX;*/
uint32_t x2 = ASMModU64ByU32RetU32(ASMMult2xU32RetU64(x1, 16807), INT32_MAX);
return *pu32Ctx = x2;
}
/** @copydoc RTRANDINT::pfnGetU32 */
static DECLCALLBACK(uint32_t) rtRandParkMillerGetU32(PRTRANDINT pThis, uint32_t u32First, uint32_t u32Last)
{
uint32_t off;
uint32_t offLast = u32Last - u32First;
if (offLast == UINT32_MAX)
{
/* 30 + 2 bit (make up for the missing INT32_MAX value) */
off = rtRandParkMillerU31(&pThis->u.ParkMiller.u32Ctx);
if (pThis->u.ParkMiller.cBits < 2)
{
pThis->u.ParkMiller.u32Bits = rtRandParkMillerU31(&pThis->u.ParkMiller.u32Ctx);
pThis->u.ParkMiller.cBits = 30;
}
off >>= 1;
off |= (pThis->u.ParkMiller.u32Bits & 3) << 30;
pThis->u.ParkMiller.u32Bits >>= 2;
pThis->u.ParkMiller.cBits -= 2;
}
else if (offLast == (uint32_t)INT32_MAX - 1)
/* The exact range. */
off = rtRandParkMillerU31(&pThis->u.ParkMiller.u32Ctx);
else if (offLast < UINT32_C(0x07ffffff))
{
/* Requested 23 or fewer bits, just lose the lower bit. */
off = rtRandParkMillerU31(&pThis->u.ParkMiller.u32Ctx);
off >>= 1;
off %= (offLast + 1);
}
else
{
/*
* 30 + 6 bits.
*/
uint64_t off64 = rtRandParkMillerU31(&pThis->u.ParkMiller.u32Ctx);
if (pThis->u.ParkMiller.cBits < 6)
{
pThis->u.ParkMiller.u32Bits = rtRandParkMillerU31(&pThis->u.ParkMiller.u32Ctx);
pThis->u.ParkMiller.cBits = 30;
}
off64 >>= 1;
off64 |= (uint64_t)(pThis->u.ParkMiller.u32Bits & 0x3f) << 30;
pThis->u.ParkMiller.u32Bits >>= 6;
pThis->u.ParkMiller.cBits -= 6;
off = ASMModU64ByU32RetU32(off64, offLast + 1);
}
return off + u32First;
}
/** @copydoc RTRANDINT::pfnSeed */
static DECLCALLBACK(int) rtRandParkMillerSeed(PRTRANDINT pThis, uint64_t u64Seed)
{
pThis->u.ParkMiller.u32Ctx = (uint32_t)u64Seed;
pThis->u.ParkMiller.u32Bits = 0;
pThis->u.ParkMiller.cBits = 0;
return VINF_SUCCESS;
}
/** @copydoc RTRANDINT::pfnSaveState */
static DECLCALLBACK(int) rtRandParkMillerSaveState(PRTRANDINT pThis, char *pszState, size_t *pcbState)
{
#define RTRAND_PARKMILLER_STATE_SIZE (3+8+1+8+1+2+1+1)
if (*pcbState < RTRAND_PARKMILLER_STATE_SIZE)
{
*pcbState = RTRAND_PARKMILLER_STATE_SIZE;
return VERR_BUFFER_OVERFLOW;
}
RTStrPrintf(pszState, *pcbState, "PM:%08RX32,%08RX32,%02x;",
pThis->u.ParkMiller.u32Ctx,
pThis->u.ParkMiller.u32Bits,
pThis->u.ParkMiller.cBits);
return VINF_SUCCESS;
}
/** @copydoc RTRANDINT::pfnRestoreState */
static DECLCALLBACK(int) rtRandParkMillerRestoreState(PRTRANDINT pThis, char const *pszState)
{
/* marker */
if ( pszState[0] != 'P'
|| pszState[1] != 'M'
|| pszState[2] != ':')
return VERR_PARSE_ERROR;
pszState += 3;
/* u32Ctx */
char *pszNext = NULL;
uint32_t u32Ctx;
int rc = RTStrToUInt32Ex(pszState, &pszNext, 16, &u32Ctx);
if ( rc != VWRN_TRAILING_CHARS
|| pszNext != pszState + 8
|| *pszNext != ',')
return VERR_PARSE_ERROR;
pszState += 8 + 1;
/* u32Bits */
uint32_t u32Bits;
rc = RTStrToUInt32Ex(pszState, &pszNext, 16, &u32Bits);
if ( rc != VWRN_TRAILING_CHARS
|| pszNext != pszState + 8
|| *pszNext != ',')
return VERR_PARSE_ERROR;
pszState += 8 + 1;
/* cBits */
uint32_t cBits;
rc = RTStrToUInt32Ex(pszState, &pszNext, 16, &cBits);
if ( rc != VWRN_TRAILING_CHARS
|| pszNext != pszState + 2
|| *pszNext != ';'
|| pszNext[1] != '\0')
return VERR_PARSE_ERROR;
/* commit */
pThis->u.ParkMiller.u32Ctx = u32Ctx;
pThis->u.ParkMiller.u32Bits = u32Bits;
pThis->u.ParkMiller.cBits = cBits;
return VINF_SUCCESS;
}
RTDECL(int) RTRandAdvCreateParkMiller(PRTRAND phRand) RT_NO_THROW_DEF
{
PRTRANDINT pThis = (PRTRANDINT)RTMemAlloc(sizeof(*pThis));
if (!pThis)
return VERR_NO_MEMORY;
pThis->u32Magic = RTRANDINT_MAGIC;
pThis->pfnGetBytes= rtRandAdvSynthesizeBytesFromU32;
pThis->pfnGetU32 = rtRandParkMillerGetU32;
pThis->pfnGetU64 = rtRandAdvSynthesizeU64FromU32;
pThis->pfnSeed = rtRandParkMillerSeed;
pThis->pfnSaveState = rtRandParkMillerSaveState;
pThis->pfnRestoreState = rtRandParkMillerRestoreState;
pThis->pfnDestroy = rtRandAdvDefaultDestroy;
pThis->u.ParkMiller.u32Ctx = 0x20080806;
pThis->u.ParkMiller.u32Bits = 0;
pThis->u.ParkMiller.cBits = 0;
*phRand = pThis;
return VINF_SUCCESS;
}
RT_EXPORT_SYMBOL(RTRandAdvCreateParkMiller);
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