// Copyright (c) 2006-2009 Nokia Corporation and/or its subsidiary(-ies).

// All rights reserved.

// This component and the accompanying materials are made available

// under the terms of "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:

//

#include "parsers.h"

// The ID3 tag has a 10 byte header.

static const TInt KID3HeaderSize = 10;

//

// Checks if an ID3 header is present at the current

// reader position, and skips over it if it is.

// Returns ETrue if a header was found, EFalse otherwise.

//

TBool TID3Parser::ReadAndSkipID3L(CReader& aReader)

	{

	TBuf8<KID3HeaderSize> header;

	TUint8 a;

	TUint8 b;

	TUint8 c;

	TUint8 d;

	header.SetLength(KID3HeaderSize);

	aReader.ReadBytesL(header);

	do

		{

		// Look for the ID3 header.

		if ((header[0] != 'I') || (header[1] != 'D') || (header[2] != '3'))

			{

			break;

			}

		// The last 4 bits of byte[5] should be zero.

		if ((header[5] & 0x0f))	// [00001111]

			{

			break;

			}

		// Read the tag size. It's stored in a sync-safe manner

		// (the highest bit is never set so it won't be confused

		// with a frame-sync). If the highest bit is set, it's invalid.

		a = header[6];

		b = header[7];

		c = header[8];

		d = header[9];

		// OR the values together and check that the highest bit of

		// the result isn't set. Saves on doing four individual checks.

		if ((a | b | c | d) & 0x80) // [10000000]

			{

			break;

			}

		// Convert from sync-safe format to normal format.

		// [0aaaaaaa][0bbbbbbb][0ccccccc][0ddddddd] is changed to

		// [0000aaaa][aaabbbbb][bbcccccc][cddddddd]

		//

		// Copy bit[0] of c into bit[7] of d.

		d |= ((c & 0x01) << 7);

		c >>= 1;

		// Copy bit[1,0] of b into bit[7,6] of c.

		c |= ((b & 0x03) << 6);

		b >>= 2;

		// Copy bit[2,1,0] of a into bit[7,6,5] of b.

		b |= ((a & 0x07) << 5);

		a >>= 3;

		TInt length = MAKE_INT32(a, b, c, d);

		aReader.SeekL(length);

		return ETrue;

		}

	while (EFalse);

	// It's not an ID3 header.

	// Undo the header read.

	aReader.SeekL(-KID3HeaderSize);

	return EFalse;

	}