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1 // Copyright (c) 2006-2009 Nokia Corporation and/or its subsidiary(-ies). |
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2 // All rights reserved. |
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3 // This component and the accompanying materials are made available |
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4 // under the terms of "Eclipse Public License v1.0" |
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5 // which accompanies this distribution, and is available |
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6 // at the URL "http://www.eclipse.org/legal/epl-v10.html". |
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7 // |
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8 // Initial Contributors: |
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9 // Nokia Corporation - initial contribution. |
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10 // |
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11 // Contributors: |
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12 // |
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13 // Description: |
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14 // |
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15 |
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16 #include "parsers.h" |
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17 |
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18 // The ID3 tag has a 10 byte header. |
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19 static const TInt KID3HeaderSize = 10; |
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20 |
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21 |
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22 // |
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23 // Checks if an ID3 header is present at the current |
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24 // reader position, and skips over it if it is. |
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25 // Returns ETrue if a header was found, EFalse otherwise. |
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26 // |
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27 TBool TID3Parser::ReadAndSkipID3L(CReader& aReader) |
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28 { |
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29 TBuf8<KID3HeaderSize> header; |
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30 TUint8 a; |
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31 TUint8 b; |
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32 TUint8 c; |
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33 TUint8 d; |
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34 |
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35 header.SetLength(KID3HeaderSize); |
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36 aReader.ReadBytesL(header); |
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37 |
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38 do |
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39 { |
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40 // Look for the ID3 header. |
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41 if ((header[0] != 'I') || (header[1] != 'D') || (header[2] != '3')) |
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42 { |
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43 break; |
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44 } |
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45 |
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46 // The last 4 bits of byte[5] should be zero. |
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47 if ((header[5] & 0x0f)) // [00001111] |
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48 { |
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49 break; |
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50 } |
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51 |
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52 // Read the tag size. It's stored in a sync-safe manner |
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53 // (the highest bit is never set so it won't be confused |
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54 // with a frame-sync). If the highest bit is set, it's invalid. |
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55 a = header[6]; |
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56 b = header[7]; |
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57 c = header[8]; |
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58 d = header[9]; |
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59 |
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60 // OR the values together and check that the highest bit of |
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61 // the result isn't set. Saves on doing four individual checks. |
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62 if ((a | b | c | d) & 0x80) // [10000000] |
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63 { |
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64 break; |
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65 } |
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66 |
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67 // Convert from sync-safe format to normal format. |
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68 // [0aaaaaaa][0bbbbbbb][0ccccccc][0ddddddd] is changed to |
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69 // [0000aaaa][aaabbbbb][bbcccccc][cddddddd] |
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70 // |
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71 // Copy bit[0] of c into bit[7] of d. |
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72 d |= ((c & 0x01) << 7); |
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73 c >>= 1; |
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74 |
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75 // Copy bit[1,0] of b into bit[7,6] of c. |
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76 c |= ((b & 0x03) << 6); |
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77 b >>= 2; |
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78 |
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79 // Copy bit[2,1,0] of a into bit[7,6,5] of b. |
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80 b |= ((a & 0x07) << 5); |
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81 a >>= 3; |
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82 |
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83 TInt length = MAKE_INT32(a, b, c, d); |
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84 aReader.SeekL(length); |
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85 return ETrue; |
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86 } |
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87 while (EFalse); |
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88 |
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89 // It's not an ID3 header. |
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90 // Undo the header read. |
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91 aReader.SeekL(-KID3HeaderSize); |
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92 return EFalse; |
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93 } |