// Copyright (c) 1994-2009 Nokia Corporation and/or its subsidiary(-ies).

// All rights reserved.

// This component and the accompanying materials are made available

// under the terms of the License "Eclipse Public License v1.0"

// which accompanies this distribution, and is available

// at the URL "http://www.eclipse.org/legal/epl-v10.html".

//

// Initial Contributors:

// Nokia Corporation - initial contribution.

//

// Contributors:

//

// Description:

// e32\kernel\random.cpp

// 

//

#include <kernel/kern_priv.h>

//

// Generate nth random number using the following algorithm

//

// X[n] = ((X[n-j] rotl r1) + (X[n-k] rotl r2)) modulo 2^b               

//

// k=17, j=10, r1=5, r2=3

//

const TInt KBufferSize=17;

const TInt KBufferSizeInBits=KBufferSize*32;

const TInt KPointer2Offset=10;  // Must be less than KBufferSize

TUint32 RandomBuffer[KBufferSize];

TInt RandomPointer=1;

TInt RandomSaltPointer=KBufferSizeInBits-1;

inline TUint32 RotateLeft5(TUint32 aVal)

	{ return (aVal << 5) | (aVal >> 27); }

inline TUint32 RotateLeft3(TUint32 aVal)

	{ return (aVal << 3) | (aVal >> 29); }

void K::Randomize()

//

// Initialise the random pool

//

	{

	TUint64 seed=K::TickQ->iRtc;

	TInt i;

	for (i=0; i<KBufferSize; i++)

		{

		RandomBuffer[i] = TUint32(seed);

		seed= ((seed<<5) + (seed>>59)) + 97;

		}

	NKern::LockSystem();

	for (i=0; i<50; i++)

		Kern::Random();

	NKern::UnlockSystem();

	}

/**

	Generate the next random number.

	@return The generated random number.

	@pre Kernel Lock must not be held.

	@pre No fast mutex should be held

	@pre Interrupts should be enabled

	@pre Can be used in a device driver.

*/

EXPORT_C TUint32 Kern::Random()

	{

	TBool alreadyLocked = TheScheduler.iLock.HeldByCurrentThread();

	if (!alreadyLocked)

		NKern::LockSystem();

	TInt p1 = RandomPointer;

	if(--p1<0)

		p1 = KBufferSize-1;

	RandomPointer = p1;

	TInt p2 = p1+KPointer2Offset;

	if(p2>KBufferSize-1)

		p2 -= KBufferSize-1;

	TUint32 r = RandomBuffer[p1] = RotateLeft5(RandomBuffer[p2])+RotateLeft3(RandomBuffer[p1]);

	if (!alreadyLocked)

		NKern::UnlockSystem();

	return r;

	}

/**

	Adds a bit to the random pool used to generate random numbers.

	This method should be used by any sources of entropy to improve the quality of

	random number generation.

	@param aBitOfSalt The least significant bit of this value is added to the random pool.

  	@pre Can be used in a device driver.

*/

EXPORT_C void Kern::RandomSalt(TUint32 aBitOfSalt)

	{

	TInt p=RandomSaltPointer; // protect RandomSaltPointer from re-entrantrancy

	if (aBitOfSalt&=1)

		{

		TInt word=p >> 5;

		TInt bit=p & 0x1f;

		RandomBuffer[word] ^= aBitOfSalt << bit;

		}

	if (--p<0)

		p=KBufferSizeInBits-1;

	RandomSaltPointer=p;

	}