1 | /* -*- C++ -*- */ |
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2 | |
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3 | /* |
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4 | |
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5 | Heap Layers: An Extensible Memory Allocation Infrastructure |
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6 | |
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7 | Copyright (C) 2000-2003 by Emery Berger |
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8 | http://www.cs.umass.edu/~emery |
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9 | emery@cs.umass.edu |
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10 | |
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11 | This program is free software; you can redistribute it and/or modify |
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12 | it under the terms of the GNU General Public License as published by |
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13 | the Free Software Foundation; either version 2 of the License, or |
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14 | (at your option) any later version. |
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15 | |
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16 | This program is distributed in the hope that it will be useful, |
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17 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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18 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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19 | GNU General Public License for more details. |
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20 | |
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21 | You should have received a copy of the GNU General Public License |
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22 | along with this program; if not, write to the Free Software |
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23 | Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
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24 | |
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25 | */ |
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26 | |
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27 | // An "Obstack". |
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28 | |
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29 | #ifndef _HLOBSTACK_H_ |
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30 | #define _HLOBSTACK_H_ |
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31 | |
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32 | #ifdef __cplusplus |
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33 | |
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34 | #include <assert.h> |
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35 | #include <new> |
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36 | |
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37 | namespace HL { |
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38 | |
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39 | template <int ChunkSize, class SuperHeap> |
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40 | class ObstackHeap : public SuperHeap { |
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41 | public: |
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42 | |
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43 | ObstackHeap (void) |
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44 | { |
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45 | // Get one chunk and set the current position marker. |
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46 | currentChunk = makeChunk (NULL, ChunkSize); |
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47 | currentBase = nextPos = (char *) (currentChunk + 1); |
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48 | assert (isValid()); |
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49 | } |
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50 | |
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51 | ~ObstackHeap (void) { |
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52 | // Free every chunk. |
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53 | assert (isValid()); |
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54 | ChunkHeader * ch = currentChunk; |
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55 | while (ch != NULL) { |
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56 | ChunkHeader * pch = ch->getPrevChunk(); |
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57 | // cout << "Freeing chunk " << ch << endl; |
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58 | SuperHeap::free (ch); |
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59 | ch = pch; |
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60 | } |
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61 | } |
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62 | |
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63 | // "Grow" the current object. |
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64 | // Returns a point in the object just before the current "grow". |
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65 | inline void * grow (size_t sz) { |
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66 | // If we've grown beyond the confines of this chunk, |
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67 | // get a new one. |
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68 | assert (isValid()); |
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69 | if ((int) ((char *) currentChunk->getLimit() - (char *) nextPos) < sz) { |
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70 | ChunkHeader * newCurrent = copyToNew(sz); |
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71 | if (newCurrent == NULL) |
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72 | return NULL; |
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73 | #if 0 |
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74 | // Now delete the previous chunk if this was the only object in it. |
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75 | if (deleteChunk != NULL) { |
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76 | SuperHeap::free (deleteChunk); |
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77 | } |
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78 | #endif |
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79 | assert (isValid()); |
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80 | } |
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81 | assert (((int) ((char *) currentChunk->getLimit() - (char *) nextPos) >= sz)); |
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82 | assert ((char *) (sz + nextPos) <= currentChunk->getLimit()); |
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83 | // Bump the pointer for the next object. |
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84 | void * prevNextPos = nextPos; |
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85 | nextPos += sz; |
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86 | assert (isValid()); |
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87 | return prevNextPos; |
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88 | } |
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89 | |
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90 | |
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91 | inline void * malloc (size_t sz) { |
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92 | assert (isValid()); |
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93 | if (currentChunk == NULL) { |
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94 | return NULL; |
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95 | } |
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96 | //sz = align(sz > 0 ? sz : 1); |
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97 | // If this object can't fit in the current chunk, |
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98 | // get another one. |
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99 | if ((int) ((char *) currentChunk->getLimit() - (char *) nextPos) < sz) { |
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100 | // Allocate a chunk that's large enough to hold the requested size. |
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101 | currentChunk = makeChunk (currentChunk, sz); |
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102 | if (currentChunk == NULL) { |
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103 | return NULL; |
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104 | } |
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105 | currentBase = nextPos = (char *) (currentChunk + 1); |
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106 | assert (isValid()); |
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107 | } |
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108 | assert (((int) ((char *) currentChunk->getLimit() - (char *) nextPos) >= sz)); |
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109 | assert ((char *) (sz + nextPos) <= currentChunk->getLimit()); |
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110 | // Bump the pointers forward. |
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111 | currentBase = nextPos; |
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112 | nextPos += sz; |
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113 | void * ptr = currentBase; |
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114 | finalize(); |
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115 | assert (isValid()); |
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116 | return (void *) ptr; |
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117 | } |
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118 | |
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119 | // Free everything allocated "after" ptr. |
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120 | // NB: Freeing NULL safely empties the entire obstack. |
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121 | inline void free (void * ptr) { |
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122 | assert (isValid()); |
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123 | // Free every chunk until we find the one that this pointer is in. |
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124 | // Then reset the current position to ptr. |
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125 | while (currentChunk != NULL && |
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126 | (((char *) currentChunk > (char *) ptr) || |
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127 | ((char *) currentChunk->getLimit() < (char *) ptr))) { |
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128 | ChunkHeader * pch = currentChunk; |
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129 | currentChunk = currentChunk->getPrevChunk(); |
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130 | SuperHeap::free (pch); |
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131 | } |
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132 | if (currentChunk != NULL) { |
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133 | currentBase = nextPos = (char *) ptr; |
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134 | assert (isValid()); |
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135 | } else { |
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136 | if (ptr != NULL) { |
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137 | // Something bad has happened -- we tried to free an item that |
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138 | // wasn't in any chunk. |
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139 | abort(); |
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140 | } else { |
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141 | // Get one chunk. |
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142 | currentChunk = makeChunk (NULL, ChunkSize); |
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143 | currentBase = nextPos = (char *) (currentChunk + 1); |
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144 | assert (isValid()); |
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145 | } |
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146 | } |
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147 | } |
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148 | |
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149 | |
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150 | inline void * getObjectBase (void) { |
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151 | assert (isValid()); |
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152 | return currentBase; |
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153 | } |
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154 | |
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155 | |
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156 | inline void finalize (void) { |
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157 | assert (isValid()); |
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158 | nextPos = (char *) align((int) nextPos); |
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159 | currentBase = nextPos; |
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160 | assert (isValid()); |
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161 | } |
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162 | |
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163 | |
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164 | private: |
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165 | |
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166 | |
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167 | inline int objectSize (void) { |
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168 | int diff = (int) (nextPos - currentBase); |
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169 | assert (diff >= 0); |
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170 | return diff; |
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171 | } |
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172 | |
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173 | |
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174 | int isValid (void) { |
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175 | // Verify class invariants. |
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176 | #ifndef NDEBUG |
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177 | bool c1 = (currentBase <= nextPos); |
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178 | assert (c1); |
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179 | bool c2 = (nextPos <= currentChunk->getLimit()); |
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180 | assert (c2); |
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181 | bool c3 = ((char *) currentChunk <= currentChunk->getLimit()); |
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182 | assert (c3); |
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183 | bool c4 = ((char *) currentChunk <= currentBase); |
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184 | assert (c4); |
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185 | bool c5 = (currentChunk != currentChunk->getPrevChunk()); |
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186 | assert (c5); |
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187 | bool c6 = (objectSize() >= 0); |
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188 | assert (c6); |
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189 | return (c1 && c2 && c3 && c4 && c5 && c6); |
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190 | #else |
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191 | return 1; |
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192 | #endif |
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193 | } |
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194 | |
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195 | // The header for every chunk. |
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196 | class ChunkHeader { |
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197 | public: |
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198 | inline ChunkHeader (ChunkHeader * prev, size_t sz) |
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199 | : _pastEnd ((char *) (this + 1) + sz), |
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200 | _prevChunk (prev) |
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201 | {} |
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202 | |
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203 | // Return the end of the current chunk. |
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204 | inline char * getLimit (void) { return _pastEnd; } |
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205 | |
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206 | // Return the previous chunk. |
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207 | inline ChunkHeader * getPrevChunk (void) { return _prevChunk; } |
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208 | |
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209 | private: |
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210 | // Just past the end of this chunk. |
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211 | char * _pastEnd; |
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212 | |
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213 | // Address of prior chunk. |
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214 | ChunkHeader * _prevChunk; |
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215 | }; |
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216 | |
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217 | |
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218 | inline static size_t align (int sz) { |
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219 | return (sz + (sizeof(double) - 1)) & ~(sizeof(double) - 1); |
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220 | } |
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221 | |
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222 | // Make a new chunk of at least sz bytes. |
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223 | inline ChunkHeader * makeChunk (ChunkHeader * ch, size_t sz) { |
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224 | // Round up the allocation size to at least one chunk. |
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225 | size_t allocSize |
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226 | = align((sz > ChunkSize - sizeof(ChunkHeader)) ? sz : ChunkSize - sizeof(ChunkHeader)); |
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227 | // Make a new chunk. |
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228 | void * ptr = SuperHeap::malloc (sizeof(ChunkHeader) + allocSize); |
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229 | if (ptr == NULL) { |
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230 | return NULL; |
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231 | } |
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232 | ChunkHeader * newChunk |
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233 | = new (ptr) ChunkHeader (ch, allocSize); |
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234 | return newChunk; |
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235 | } |
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236 | |
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237 | |
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238 | // Copy the current object to a new chunk. |
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239 | // sz = the minimum amount of extra space we need. |
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240 | inline ChunkHeader * copyToNew (size_t sz) { |
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241 | size_t obj_size = objectSize(); |
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242 | size_t new_size = obj_size + sz + (obj_size >> 3) + 100; |
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243 | //size_t new_size = 2 * (obj_size + sz); |
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244 | ChunkHeader * newChunk; |
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245 | #if 0 |
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246 | // This variable will hold the chunk to be deleted (if any). |
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247 | ChunkHeader * deleteChunk = NULL; |
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248 | // If this object was the only one in the chunk, |
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249 | // link back past this chunk. |
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250 | if (currentBase == (char *) (currentChunk + 1)) { |
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251 | newChunk = makeChunk (currentChunk->getPrevChunk(), new_size); |
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252 | deleteChunk = currentChunk; |
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253 | } else { |
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254 | newChunk = makeChunk (currentChunk, new_size); |
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255 | } |
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256 | #else |
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257 | newChunk = makeChunk (currentChunk, new_size); |
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258 | #endif |
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259 | if (newChunk == NULL) { |
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260 | currentChunk = NULL; |
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261 | return NULL; |
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262 | } |
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263 | // Copy the current object to the new chunk. |
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264 | memcpy ((char *) (newChunk + 1), currentBase, obj_size); |
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265 | currentChunk = newChunk; |
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266 | currentBase = (char *) (currentChunk + 1); |
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267 | nextPos = currentBase + obj_size; |
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268 | #if 0 |
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269 | if (deleteChunk != NULL) { |
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270 | SuperHeap::free (deleteChunk); |
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271 | } |
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272 | #endif |
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273 | return currentChunk; |
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274 | } |
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275 | |
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276 | |
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277 | // Current position in the current chunk. |
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278 | char * currentBase; |
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279 | |
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280 | // Where to add the next character to the current object. |
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281 | char * nextPos; |
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282 | |
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283 | // My current chunk. |
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284 | ChunkHeader * currentChunk; |
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285 | |
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286 | }; |
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287 | |
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288 | }; |
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289 | |
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290 | #endif // __cplusplus |
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291 | |
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292 | #endif // _HLOBSTACK_H_ |
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