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1 /*******************************************************************************
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2 * Copyright (c) 2000, 2008 IBM Corporation and others.
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3 * All rights reserved. This program and the accompanying materials
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4 * are made available under the terms of the Eclipse Public License v1.0
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5 * which accompanies this distribution, and is available at
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6 * http://www.eclipse.org/legal/epl-v10.html
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7 *
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8 * Contributors:
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9 * IBM Corporation - initial API and implementation
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10 * Port to the D programming language:
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11 * Frank Benoit <benoit@tionex.de>
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12 *******************************************************************************/
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13 module dwtx.jface.text.GapTextStore;
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14
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15 import dwt.dwthelper.utils;
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16
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17 import dwtx.core.runtime.Assert;
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18
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19
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20 /**
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21 * Implements a gap managing text store. The gap text store relies on the assumption that
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22 * consecutive changes to a document are co-located. The start of the gap is always moved to the
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23 * location of the last change.
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24 * <p>
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25 * <strong>Performance:</strong> Typing-style changes perform in constant time unless re-allocation
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26 * becomes necessary. Generally, a change that does not cause re-allocation will cause at most one
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27 * {@linkplain System#arraycopy(Object, int, Object, int, int) arraycopy} operation of a length of
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28 * about <var>d</var>, where <var>d</var> is the distance from the previous change. Let <var>a(x)</var>
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29 * be the algorithmic performance of an <code>arraycopy</code> operation of the length <var>x</var>,
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30 * then such a change then performs in <i>O(a(x))</i>,
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31 * {@linkplain #get(int, int) get(int, <var>length</var>)} performs in <i>O(a(length))</i>,
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32 * {@link #get(int)} in <i>O(1)</i>.
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33 * <p>
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34 * How frequently the array needs re-allocation is controlled by the constructor parameters.
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35 * </p>
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36 * <p>
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37 * This class is not intended to be subclassed.
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38 * </p>
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39 *
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40 * @see CopyOnWriteTextStore for a copy-on-write text store wrapper
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41 * @noextend This class is not intended to be subclassed by clients.
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42 */
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43 public class GapTextStore : ITextStore {
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44 /**
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45 * The minimum gap size allocated when re-allocation occurs.
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46 * @since 3.3
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47 */
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48 private final int fMinGapSize;
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49 /**
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50 * The maximum gap size allocated when re-allocation occurs.
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51 * @since 3.3
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52 */
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53 private final int fMaxGapSize;
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54 /**
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55 * The multiplier to compute the array size from the content length
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56 * (1 <= fSizeMultiplier <= 2).
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57 *
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58 * @since 3.3
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59 */
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60 private final float fSizeMultiplier;
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61
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62 /** The store's content */
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63 private char[] fContent= new char[0];
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64 /** Starting index of the gap */
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65 private int fGapStart= 0;
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66 /** End index of the gap */
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67 private int fGapEnd= 0;
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68 /**
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69 * The current high water mark. If a change would cause the gap to grow larger than this, the
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70 * array is re-allocated.
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71 * @since 3.3
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72 */
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73 private int fThreshold= 0;
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74
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75 /**
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76 * Creates a new empty text store using the specified low and high watermarks.
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77 *
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78 * @param lowWatermark unused - at the lower bound, the array is only resized when the content
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79 * does not fit
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80 * @param highWatermark if the gap is ever larger than this, it will automatically be shrunken
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81 * (>= 0)
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82 * @deprecated use {@link GapTextStore#GapTextStore(int, int, float)} instead
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83 */
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84 public GapTextStore(int lowWatermark, int highWatermark) {
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85 /*
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86 * Legacy constructor. The API contract states that highWatermark is the upper bound for the
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87 * gap size. Albeit this contract was not previously adhered to, it is now: The allocated
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88 * gap size is fixed at half the highWatermark. Since the threshold is always twice the
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89 * allocated gap size, the gap will never grow larger than highWatermark. Previously, the
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90 * gap size was initialized to highWatermark, causing re-allocation if the content length
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91 * shrunk right after allocation. The fixed gap size is now only half of the previous value,
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92 * circumventing that problem (there was no API contract specifying the initial gap size).
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93 *
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94 * The previous implementation did not allow the gap size to become smaller than
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95 * lowWatermark, which doesn't make any sense: that area of the gap was simply never ever
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96 * used.
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97 */
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98 this(highWatermark / 2, highWatermark / 2, 0f);
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99 }
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100
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101 /**
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102 * Equivalent to
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103 * {@linkplain GapTextStore#GapTextStore(int, int, float) new GapTextStore(256, 4096, 0.1f)}.
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104 *
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105 * @since 3.3
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106 */
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107 public GapTextStore() {
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108 this(256, 4096, 0.1f);
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109 }
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110
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111 /**
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112 * Creates an empty text store that uses re-allocation thresholds relative to the content
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113 * length. Re-allocation is controlled by the <em>gap factor</em>, which is the quotient of
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114 * the gap size and the array size. Re-allocation occurs if a change causes the gap factor to go
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115 * outside <code>[0, maxGapFactor]</code>. When re-allocation occurs, the array is sized
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116 * such that the gap factor is <code>0.5 * maxGapFactor</code>. The gap size computed in this
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117 * manner is bounded by the <code>minSize</code> and <code>maxSize</code> parameters.
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118 * <p>
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119 * A <code>maxGapFactor</code> of <code>0</code> creates a text store that never has a gap
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120 * at all (if <code>minSize</code> is 0); a <code>maxGapFactor</code> of <code>1</code>
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121 * creates a text store that doubles its size with every re-allocation and that never shrinks.
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122 * </p>
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123 * <p>
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124 * The <code>minSize</code> and <code>maxSize</code> parameters are absolute bounds to the
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125 * allocated gap size. Use <code>minSize</code> to avoid frequent re-allocation for small
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126 * documents. Use <code>maxSize</code> to avoid a huge gap being allocated for large
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127 * documents.
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128 * </p>
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129 *
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130 * @param minSize the minimum gap size to allocate (>= 0; use 0 for no minimum)
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131 * @param maxSize the maximum gap size to allocate (>= minSize; use
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132 * {@link Integer#MAX_VALUE} for no maximum)
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133 * @param maxGapFactor is the maximum fraction of the array that is occupied by the gap (<code>0 <= maxGapFactor <= 1</code>)
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134 * @since 3.3
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135 */
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136 public GapTextStore(int minSize, int maxSize, float maxGapFactor) {
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137 Assert.isLegal(0f <= maxGapFactor && maxGapFactor <= 1f);
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138 Assert.isLegal(0 <= minSize && minSize <= maxSize);
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139 fMinGapSize= minSize;
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140 fMaxGapSize= maxSize;
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141 fSizeMultiplier= 1 / (1 - maxGapFactor / 2);
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142 }
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143
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144 /*
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145 * @see dwtx.jface.text.ITextStore#get(int)
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146 */
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147 public final char get(int offset) {
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148 if (offset < fGapStart)
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149 return fContent[offset];
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150
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151 return fContent[offset + gapSize()];
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152 }
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153
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154 /*
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155 * @see dwtx.jface.text.ITextStore#get(int, int)
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156 */
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157 public final String get(int offset, int length) {
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158 if (fGapStart <= offset)
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159 return new String(fContent, offset + gapSize() , length);
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160
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161 final int end= offset + length;
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162
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163 if (end <= fGapStart)
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164 return new String(fContent, offset, length);
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165
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166 StringBuffer buf= new StringBuffer(length);
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167 buf.append(fContent, offset, fGapStart - offset);
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168 buf.append(fContent, fGapEnd, end - fGapStart);
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169 return buf.toString();
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170 }
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171
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172 /*
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173 * @see dwtx.jface.text.ITextStore#getLength()
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174 */
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175 public final int getLength() {
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176 return fContent.length - gapSize();
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177 }
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178
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179 /*
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180 * @see dwtx.jface.text.ITextStore#set(java.lang.String)
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181 */
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182 public final void set(String text) {
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183 /*
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184 * Moves the gap to the end of the content. There is no sensible prediction of where the
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185 * next change will occur, but at least the next change will not trigger re-allocation. This
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186 * is especially important when using the GapTextStore within a CopyOnWriteTextStore, where
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187 * the GTS is only initialized right before a modification.
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188 */
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189 replace(0, getLength(), text);
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190 }
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191
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192 /*
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193 * @see dwtx.jface.text.ITextStore#replace(int, int, java.lang.String)
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194 */
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195 public final void replace(int offset, int length, String text) {
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196 if (text is null) {
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197 adjustGap(offset, length, 0);
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198 } else {
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199 int textLength= text.length();
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200 adjustGap(offset, length, textLength);
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201 if (textLength !is 0)
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202 text.getChars(0, textLength, fContent, offset);
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203 }
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204 }
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205
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206 /**
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207 * Moves the gap to <code>offset + add</code>, moving any content after
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208 * <code>offset + remove</code> behind the gap. The gap size is kept between 0 and
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209 * {@link #fThreshold}, leading to re-allocation if needed. The content between
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210 * <code>offset</code> and <code>offset + add</code> is undefined after this operation.
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211 *
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212 * @param offset the offset at which a change happens
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213 * @param remove the number of character which are removed or overwritten at <code>offset</code>
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214 * @param add the number of character which are inserted or overwriting at <code>offset</code>
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215 */
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216 private void adjustGap(int offset, int remove, int add) {
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217 final int oldGapSize= gapSize();
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218 final int newGapSize= oldGapSize - add + remove;
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219 final bool reuseArray= 0 <= newGapSize && newGapSize <= fThreshold;
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220
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221 final int newGapStart= offset + add;
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222 final int newGapEnd;
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223
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224 if (reuseArray)
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225 newGapEnd= moveGap(offset, remove, oldGapSize, newGapSize, newGapStart);
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226 else
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227 newGapEnd= reallocate(offset, remove, oldGapSize, newGapSize, newGapStart);
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228
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229 fGapStart= newGapStart;
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230 fGapEnd= newGapEnd;
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231 }
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232
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233 /**
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234 * Moves the gap to <code>newGapStart</code>.
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235 *
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236 * @param offset the change offset
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237 * @param remove the number of removed / overwritten characters
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238 * @param oldGapSize the old gap size
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239 * @param newGapSize the gap size after the change
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240 * @param newGapStart the offset in the array to move the gap to
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241 * @return the new gap end
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242 * @since 3.3
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243 */
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244 private int moveGap(int offset, int remove, int oldGapSize, int newGapSize, int newGapStart) {
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245 /*
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246 * No re-allocation necessary. The area between the change offset and gap can be copied
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247 * in at most one operation. Don't copy parts that will be overwritten anyway.
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248 */
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249 final int newGapEnd= newGapStart + newGapSize;
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250 if (offset < fGapStart) {
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251 int afterRemove= offset + remove;
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252 if (afterRemove < fGapStart) {
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253 final int betweenSize= fGapStart - afterRemove;
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254 arrayCopy(afterRemove, fContent, newGapEnd, betweenSize);
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255 }
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256 // otherwise, only the gap gets enlarged
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257 } else {
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258 final int offsetShifted= offset + oldGapSize;
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259 final int betweenSize= offsetShifted - fGapEnd; // in the typing case, betweenSize is 0
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260 arrayCopy(fGapEnd, fContent, fGapStart, betweenSize);
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261 }
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262 return newGapEnd;
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263 }
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264
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265 /**
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266 * Reallocates a new array and copies the data from the previous one.
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267 *
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268 * @param offset the change offset
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269 * @param remove the number of removed / overwritten characters
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270 * @param oldGapSize the old gap size
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271 * @param newGapSize the gap size after the change if no re-allocation would occur (can be negative)
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272 * @param newGapStart the offset in the array to move the gap to
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273 * @return the new gap end
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274 * @since 3.3
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275 */
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276 private int reallocate(int offset, int remove, final int oldGapSize, int newGapSize, final int newGapStart) {
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277 // the new content length (without any gap)
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278 final int newLength= fContent.length - newGapSize;
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279 // the new array size based on the gap factor
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280 int newArraySize= (int) (newLength * fSizeMultiplier);
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281 newGapSize= newArraySize - newLength;
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282
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283 // bound the gap size within min/max
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284 if (newGapSize < fMinGapSize) {
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285 newGapSize= fMinGapSize;
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286 newArraySize= newLength + newGapSize;
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287 } else if (newGapSize > fMaxGapSize) {
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288 newGapSize= fMaxGapSize;
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289 newArraySize= newLength + newGapSize;
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290 }
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291
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292 // the upper threshold is always twice the gapsize
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293 fThreshold= newGapSize * 2;
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294 final char[] newContent= allocate(newArraySize);
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295 final int newGapEnd= newGapStart + newGapSize;
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296
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297 /*
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298 * Re-allocation: The old content can be copied in at most 3 operations to the newly allocated
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299 * array. Either one of change offset and the gap may come first.
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300 * - unchanged area before the change offset / gap
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301 * - area between the change offset and the gap (either one may be first)
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302 * - rest area after the change offset / after the gap
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303 */
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304 if (offset < fGapStart) {
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305 // change comes before gap
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306 arrayCopy(0, newContent, 0, offset);
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307 int afterRemove= offset + remove;
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308 if (afterRemove < fGapStart) {
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309 // removal is completely before the gap
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310 final int betweenSize= fGapStart - afterRemove;
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311 arrayCopy(afterRemove, newContent, newGapEnd, betweenSize);
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312 final int restSize= fContent.length - fGapEnd;
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313 arrayCopy(fGapEnd, newContent, newGapEnd + betweenSize, restSize);
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314 } else {
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315 // removal encompasses the gap
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316 afterRemove += oldGapSize;
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317 final int restSize= fContent.length - afterRemove;
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318 arrayCopy(afterRemove, newContent, newGapEnd, restSize);
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319 }
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320 } else {
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321 // gap comes before change
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322 arrayCopy(0, newContent, 0, fGapStart);
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323 final int offsetShifted= offset + oldGapSize;
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324 final int betweenSize= offsetShifted - fGapEnd;
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325 arrayCopy(fGapEnd, newContent, fGapStart, betweenSize);
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326 final int afterRemove= offsetShifted + remove;
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327 final int restSize= fContent.length - afterRemove;
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328 arrayCopy(afterRemove, newContent, newGapEnd, restSize);
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329 }
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330
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331 fContent= newContent;
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332 return newGapEnd;
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333 }
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334
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335 /**
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336 * Allocates a new <code>char[size]</code>.
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337 *
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338 * @param size the length of the new array.
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339 * @return a newly allocated char array
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340 * @since 3.3
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341 */
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342 private char[] allocate(int size) {
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343 return new char[size];
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344 }
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345
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346 /*
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347 * Executes System.arraycopy if length !is 0. A length < 0 cannot happen -> don't hide coding
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348 * errors by checking for negative lengths.
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349 * @since 3.3
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350 */
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351 private void arrayCopy(int srcPos, char[] dest, int destPos, int length) {
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352 if (length !is 0)
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353 System.arraycopy(fContent, srcPos, dest, destPos, length);
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354 }
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355
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356 /**
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357 * Returns the gap size.
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358 *
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359 * @return the gap size
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360 * @since 3.3
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361 */
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362 private int gapSize() {
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363 return fGapEnd - fGapStart;
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364 }
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365
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366 /**
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367 * Returns a copy of the content of this text store.
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368 * For internal use only.
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369 *
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370 * @return a copy of the content of this text store
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371 */
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372 protected String getContentAsString() {
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373 return new String(fContent);
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374 }
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375
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376 /**
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377 * Returns the start index of the gap managed by this text store.
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378 * For internal use only.
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379 *
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380 * @return the start index of the gap managed by this text store
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381 */
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382 protected int getGapStartIndex() {
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383 return fGapStart;
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384 }
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385
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386 /**
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387 * Returns the end index of the gap managed by this text store.
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388 * For internal use only.
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389 *
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390 * @return the end index of the gap managed by this text store
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391 */
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392 protected int getGapEndIndex() {
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393 return fGapEnd;
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394 }
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395 }
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