sl@0: // Copyright (c) 2006-2009 Nokia Corporation and/or its subsidiary(-ies).
sl@0: // All rights reserved.
sl@0: // This component and the accompanying materials are made available
sl@0: // under the terms of "Eclipse Public License v1.0"
sl@0: // which accompanies this distribution, and is available
sl@0: // at the URL "http://www.eclipse.org/legal/epl-v10.html".
sl@0: //
sl@0: // Initial Contributors:
sl@0: // Nokia Corporation - initial contribution.
sl@0: //
sl@0: // Contributors:
sl@0: //
sl@0: // Description:
sl@0: //
sl@0: 
sl@0: #include "parsers.h"
sl@0: 
sl@0: // The ID3 tag has a 10 byte header.
sl@0: static const TInt KID3HeaderSize = 10;
sl@0: 
sl@0: 
sl@0: //
sl@0: // Checks if an ID3 header is present at the current
sl@0: // reader position, and skips over it if it is.
sl@0: // Returns ETrue if a header was found, EFalse otherwise.
sl@0: //
sl@0: TBool TID3Parser::ReadAndSkipID3L(CReader& aReader)
sl@0: 	{
sl@0: 	TBuf8<KID3HeaderSize> header;
sl@0: 	TUint8 a;
sl@0: 	TUint8 b;
sl@0: 	TUint8 c;
sl@0: 	TUint8 d;
sl@0: 	
sl@0: 	header.SetLength(KID3HeaderSize);
sl@0: 	aReader.ReadBytesL(header);
sl@0: 	
sl@0: 	do
sl@0: 		{
sl@0: 		// Look for the ID3 header.
sl@0: 		if ((header[0] != 'I') || (header[1] != 'D') || (header[2] != '3'))
sl@0: 			{
sl@0: 			break;
sl@0: 			}
sl@0: 			
sl@0: 		// The last 4 bits of byte[5] should be zero.
sl@0: 		if ((header[5] & 0x0f))	// [00001111]
sl@0: 			{
sl@0: 			break;
sl@0: 			}
sl@0: 			
sl@0: 		// Read the tag size. It's stored in a sync-safe manner
sl@0: 		// (the highest bit is never set so it won't be confused
sl@0: 		// with a frame-sync). If the highest bit is set, it's invalid.
sl@0: 		a = header[6];
sl@0: 		b = header[7];
sl@0: 		c = header[8];
sl@0: 		d = header[9];
sl@0: 		
sl@0: 		// OR the values together and check that the highest bit of
sl@0: 		// the result isn't set. Saves on doing four individual checks.
sl@0: 		if ((a | b | c | d) & 0x80) // [10000000]
sl@0: 			{
sl@0: 			break;
sl@0: 			}
sl@0: 		
sl@0: 		// Convert from sync-safe format to normal format.
sl@0: 		// [0aaaaaaa][0bbbbbbb][0ccccccc][0ddddddd] is changed to
sl@0: 		// [0000aaaa][aaabbbbb][bbcccccc][cddddddd]
sl@0: 		//
sl@0: 		// Copy bit[0] of c into bit[7] of d.
sl@0: 		d |= ((c & 0x01) << 7);
sl@0: 		c >>= 1;
sl@0: 		
sl@0: 		// Copy bit[1,0] of b into bit[7,6] of c.
sl@0: 		c |= ((b & 0x03) << 6);
sl@0: 		b >>= 2;
sl@0: 		
sl@0: 		// Copy bit[2,1,0] of a into bit[7,6,5] of b.
sl@0: 		b |= ((a & 0x07) << 5);
sl@0: 		a >>= 3;
sl@0: 		
sl@0: 		TInt length = MAKE_INT32(a, b, c, d);
sl@0: 		aReader.SeekL(length);
sl@0: 		return ETrue;
sl@0: 		}
sl@0: 	while (EFalse);
sl@0: 	
sl@0: 	// It's not an ID3 header.
sl@0: 	// Undo the header read.
sl@0: 	aReader.SeekL(-KID3HeaderSize);
sl@0: 	return EFalse;
sl@0: 	}