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1 // Copyright (c) 2010 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 // dictionarycompression.cpp |
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15 // |
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16 /** |
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17 * @file dictionarycompression.cpp |
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18 * |
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19 * @internalComponent |
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20 * @released |
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21 */ |
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22 |
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23 #include "dictionarycompression.h" |
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24 |
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25 RDictionaryCompressionBitStream::RDictionaryCompressionBitStream() : |
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26 iNumberOfBitsUsedForDictionaryTokens(0), |
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27 iOffsetToFirstBit(-1), |
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28 iOffsetToCurrentBit(-1), |
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29 iOffsetOnePastLastBit(-1), |
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30 iOwnsBitBuffer(false), |
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31 iBuffer(NULL) |
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32 { |
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33 } |
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34 |
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35 void RDictionaryCompressionBitStream::OpenL( |
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36 TInt aNumberOfBitsUsedForDictionaryTokens, |
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37 TInt aOffsetToFirstBit, |
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38 TInt aOffsetOnePastLastBit, |
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39 TBool aTransferringOwnershipOfBuffer, |
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40 TUint8* aBuffer) |
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41 { |
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42 iNumberOfBitsUsedForDictionaryTokens = aNumberOfBitsUsedForDictionaryTokens; |
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43 iOffsetToFirstBit = aOffsetToFirstBit; |
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44 iOffsetToCurrentBit = aOffsetToFirstBit; |
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45 iOffsetOnePastLastBit = aOffsetOnePastLastBit; |
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46 iOwnsBitBuffer = aTransferringOwnershipOfBuffer; |
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47 iBuffer = aBuffer; |
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48 |
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49 assert(aBuffer!=NULL); |
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50 assert(aOffsetToFirstBit >= 0); |
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51 assert(aOffsetToFirstBit<=aOffsetOnePastLastBit); |
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52 } |
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53 |
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54 void RDictionaryCompressionBitStream::Close() |
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55 { |
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56 if (iOwnsBitBuffer) |
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57 { |
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58 iOwnsBitBuffer=EFalse; |
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59 delete [] iBuffer; |
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60 } |
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61 iBuffer=NULL; |
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62 } |
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63 |
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64 TBool RDictionaryCompressionBitStream::EndOfStreamL() const |
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65 { |
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66 assert(iBuffer!=NULL); |
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67 assert(iOffsetToFirstBit >= 0); |
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68 assert(iOffsetToCurrentBit>=iOffsetToFirstBit); |
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69 assert(iOffsetToCurrentBit<=iOffsetOnePastLastBit); |
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70 return iOffsetToCurrentBit>=iOffsetOnePastLastBit; |
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71 } |
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72 |
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73 TInt RDictionaryCompressionBitStream::IndexOfDictionaryEntryL() |
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74 { |
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75 // increments the current bit-position if it returns a value >=0; returns KErrNotFound if the next thing in the stream is plain data rather than the index of a dictionary entry |
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76 assert(iBuffer!=NULL); |
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77 assert(!EndOfStreamL()); |
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78 if (!CurrentBitIsOn()) |
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79 { |
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80 ++iOffsetToCurrentBit; |
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81 return ReadIntegerL(iNumberOfBitsUsedForDictionaryTokens); |
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82 } |
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83 return KErrNotFound; |
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84 } |
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85 |
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86 void RDictionaryCompressionBitStream::ReadL(Ptr8 aBufferToAppendTo,TBool aCalypsoFileFormat) |
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87 { |
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88 // can only be called if IndexOfDictionaryEntry returned a negative value |
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89 assert(iBuffer!=NULL); |
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90 assert(!EndOfStreamL()); |
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91 TInt numberOfConsecutivePrefixBits=0; |
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92 TInt i; |
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93 for (i=0; i<4; ++i) |
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94 { |
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95 const TBool currentBitIsOn=CurrentBitIsOn(); |
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96 ++iOffsetToCurrentBit; // increment this regardless whether the current bit is on |
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97 if (!currentBitIsOn) |
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98 { |
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99 break; |
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100 } |
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101 ++numberOfConsecutivePrefixBits; |
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102 } |
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103 assert(numberOfConsecutivePrefixBits>0); |
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104 assert(numberOfConsecutivePrefixBits<=4); |
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105 TInt numberOfBytesToRead = numberOfConsecutivePrefixBits; |
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106 if (numberOfConsecutivePrefixBits==3) |
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107 { |
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108 numberOfBytesToRead=3+ReadIntegerL(3); |
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109 } |
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110 else if (numberOfConsecutivePrefixBits==4) |
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111 { |
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112 numberOfBytesToRead=ReadIntegerL(8); |
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113 if (!aCalypsoFileFormat) |
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114 { |
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115 numberOfBytesToRead+=3+(1<<3); |
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116 } |
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117 } |
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118 |
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119 const TInt numberOfBitsOffByteBoundary=iOffsetToCurrentBit%8; |
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120 const TUint8* currentByte=iBuffer+(iOffsetToCurrentBit/8); |
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121 assert((numberOfBytesToRead + aBufferToAppendTo.GetLength()) <= aBufferToAppendTo.GetMaxLength()); |
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122 for (i=0; i<numberOfBytesToRead; ++i, ++currentByte) |
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123 { |
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124 TUint byte=*currentByte; |
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125 assert(numberOfBitsOffByteBoundary>=0); |
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126 if (numberOfBitsOffByteBoundary>0) |
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127 { |
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128 byte>>=numberOfBitsOffByteBoundary; |
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129 byte|=(*(currentByte+1)<<(8-numberOfBitsOffByteBoundary)); |
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130 byte&=0xff; |
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131 } |
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132 aBufferToAppendTo.Append(byte,1); |
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133 } |
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134 iOffsetToCurrentBit+=numberOfBytesToRead*8; |
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135 assert(numberOfBitsOffByteBoundary==iOffsetToCurrentBit%8); |
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136 } |
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137 |
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138 TBool RDictionaryCompressionBitStream::CurrentBitIsOn() const |
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139 { |
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140 // does not increment the current bit-position |
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141 assert(iBuffer!=NULL); |
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142 return iBuffer[iOffsetToCurrentBit/8]&(1<<(iOffsetToCurrentBit%8)); |
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143 } |
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144 |
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145 TUint RDictionaryCompressionBitStream::ReadIntegerL(TInt aNumberOfBits) |
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146 { |
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147 // increments the current bit-position |
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148 assert(iBuffer!=NULL); |
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149 TInt integer=0; |
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150 TInt numberOfBitsLeftToRead=aNumberOfBits; |
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151 // FOREVER |
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152 while(1) |
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153 { |
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154 const TInt offsetToFirstBitToReadInCurrentByte=iOffsetToCurrentBit%8; |
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155 const TInt offsetOnePastLastBitToReadInCurrentByte=Min(8,offsetToFirstBitToReadInCurrentByte+numberOfBitsLeftToRead); |
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156 const TInt numberOfBitsReadFromCurrentByte=offsetOnePastLastBitToReadInCurrentByte-offsetToFirstBitToReadInCurrentByte; |
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157 assert(numberOfBitsReadFromCurrentByte>0); |
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158 const TUint bitsReadFromCurrentByte=((iBuffer[iOffsetToCurrentBit/8]>>offsetToFirstBitToReadInCurrentByte)&((1<<numberOfBitsReadFromCurrentByte)-1)); |
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159 integer|=(bitsReadFromCurrentByte<<(aNumberOfBits-numberOfBitsLeftToRead)); |
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160 iOffsetToCurrentBit+=numberOfBitsReadFromCurrentByte; |
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161 numberOfBitsLeftToRead-=numberOfBitsReadFromCurrentByte; |
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162 assert(numberOfBitsLeftToRead>=0); |
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163 if (numberOfBitsLeftToRead<=0) |
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164 { |
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165 break; |
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166 } |
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167 } |
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168 return integer; |
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169 } |
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170 |