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799
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1 /* vi:set ts=8 sts=4 sw=4:
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2 *
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3 * VIM - Vi IMproved by Bram Moolenaar
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4 *
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5 * Do ":help uganda" in Vim to read copying and usage conditions.
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6 * Do ":help credits" in Vim to see a list of people who contributed.
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7 * See README.txt for an overview of the Vim source code.
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8 */
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9
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10 /*
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11 * hashtab.c: Handling of a hashtable with Vim-specific properties.
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12 *
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13 * Each item in a hashtable has a NUL terminated string key. A key can appear
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14 * only once in the table.
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15 *
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16 * A hash number is computed from the key for quick lookup. When the hashes
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17 * of two different keys point to the same entry an algorithm is used to
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18 * iterate over other entries in the table until the right one is found.
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19 * To make the iteration work removed keys are different from entries where a
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20 * key was never present.
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21 *
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22 * The mechanism has been partly based on how Python Dictionaries are
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23 * implemented. The algorithm is from Knuth Vol. 3, Sec. 6.4.
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24 *
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25 * The hashtable grows to accommodate more entries when needed. At least 1/3
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26 * of the entries is empty to keep the lookup efficient (at the cost of extra
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27 * memory).
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28 */
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29
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30 #include "vim.h"
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31
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32 #if defined(FEAT_EVAL) || defined(FEAT_SYN_HL) || defined(PROTO)
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33
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34 #if 0
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35 # define HT_DEBUG /* extra checks for table consistency and statistics */
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36
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37 static long hash_count_lookup = 0; /* count number of hashtab lookups */
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38 static long hash_count_perturb = 0; /* count number of "misses" */
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39 #endif
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40
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41 /* Magic value for algorithm that walks through the array. */
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42 #define PERTURB_SHIFT 5
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43
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44 static int hash_may_resize __ARGS((hashtab_T *ht, int minitems));
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45
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46 #if 0 /* currently not used */
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47 /*
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48 * Create an empty hash table.
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49 * Returns NULL when out of memory.
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50 */
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51 hashtab_T *
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52 hash_create()
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53 {
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54 hashtab_T *ht;
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55
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56 ht = (hashtab_T *)alloc(sizeof(hashtab_T));
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57 if (ht != NULL)
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58 hash_init(ht);
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59 return ht;
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60 }
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61 #endif
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62
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63 /*
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64 * Initialize an empty hash table.
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65 */
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66 void
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67 hash_init(ht)
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68 hashtab_T *ht;
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69 {
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70 /* This zeroes all "ht_" entries and all the "hi_key" in "ht_smallarray". */
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71 vim_memset(ht, 0, sizeof(hashtab_T));
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72 ht->ht_array = ht->ht_smallarray;
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73 ht->ht_mask = HT_INIT_SIZE - 1;
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74 }
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75
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76 /*
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77 * Free the array of a hash table. Does not free the items it contains!
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78 * If "ht" is not freed then you should call hash_init() next!
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79 */
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80 void
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81 hash_clear(ht)
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82 hashtab_T *ht;
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83 {
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84 if (ht->ht_array != ht->ht_smallarray)
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85 vim_free(ht->ht_array);
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86 }
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87
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88 /*
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89 * Free the array of a hash table and all the keys it contains. The keys must
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90 * have been allocated. "off" is the offset from the start of the allocate
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91 * memory to the location of the key (it's always positive).
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92 */
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93 void
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94 hash_clear_all(ht, off)
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95 hashtab_T *ht;
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96 int off;
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97 {
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835
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98 long todo;
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799
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99 hashitem_T *hi;
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100
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835
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101 todo = (long)ht->ht_used;
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799
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102 for (hi = ht->ht_array; todo > 0; ++hi)
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103 {
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104 if (!HASHITEM_EMPTY(hi))
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105 {
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106 vim_free(hi->hi_key - off);
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107 --todo;
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108 }
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109 }
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110 hash_clear(ht);
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111 }
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112
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113 /*
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114 * Find "key" in hashtable "ht". "key" must not be NULL.
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115 * Always returns a pointer to a hashitem. If the item was not found then
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116 * HASHITEM_EMPTY() is TRUE. The pointer is then the place where the key
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117 * would be added.
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118 * WARNING: The returned pointer becomes invalid when the hashtable is changed
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119 * (adding, setting or removing an item)!
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120 */
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121 hashitem_T *
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122 hash_find(ht, key)
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123 hashtab_T *ht;
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124 char_u *key;
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125 {
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126 return hash_lookup(ht, key, hash_hash(key));
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127 }
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128
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129 /*
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130 * Like hash_find(), but caller computes "hash".
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131 */
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132 hashitem_T *
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133 hash_lookup(ht, key, hash)
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134 hashtab_T *ht;
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135 char_u *key;
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136 hash_T hash;
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137 {
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138 hash_T perturb;
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139 hashitem_T *freeitem;
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140 hashitem_T *hi;
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141 int idx;
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142
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143 #ifdef HT_DEBUG
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144 ++hash_count_lookup;
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145 #endif
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146
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147 /*
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148 * Quickly handle the most common situations:
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149 * - return if there is no item at all
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150 * - skip over a removed item
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151 * - return if the item matches
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152 */
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835
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153 idx = (int)(hash & ht->ht_mask);
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799
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154 hi = &ht->ht_array[idx];
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155
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156 if (hi->hi_key == NULL)
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157 return hi;
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158 if (hi->hi_key == HI_KEY_REMOVED)
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159 freeitem = hi;
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160 else if (hi->hi_hash == hash && STRCMP(hi->hi_key, key) == 0)
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161 return hi;
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162 else
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163 freeitem = NULL;
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164
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165 /*
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166 * Need to search through the table to find the key. The algorithm
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167 * to step through the table starts with large steps, gradually becoming
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168 * smaller down to (1/4 table size + 1). This means it goes through all
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169 * table entries in the end.
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170 * When we run into a NULL key it's clear that the key isn't there.
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171 * Return the first available slot found (can be a slot of a removed
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172 * item).
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173 */
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174 for (perturb = hash; ; perturb >>= PERTURB_SHIFT)
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175 {
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176 #ifdef HT_DEBUG
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177 ++hash_count_perturb; /* count a "miss" for hashtab lookup */
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178 #endif
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835
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179 idx = (int)((idx << 2) + idx + perturb + 1);
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799
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180 hi = &ht->ht_array[idx & ht->ht_mask];
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181 if (hi->hi_key == NULL)
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182 return freeitem == NULL ? hi : freeitem;
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183 if (hi->hi_hash == hash
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184 && hi->hi_key != HI_KEY_REMOVED
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185 && STRCMP(hi->hi_key, key) == 0)
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186 return hi;
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187 if (hi->hi_key == HI_KEY_REMOVED && freeitem == NULL)
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188 freeitem = hi;
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189 }
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190 }
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191
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192 /*
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193 * Print the efficiency of hashtable lookups.
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194 * Useful when trying different hash algorithms.
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195 * Called when exiting.
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196 */
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197 void
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198 hash_debug_results()
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199 {
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200 #ifdef HT_DEBUG
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201 fprintf(stderr, "\r\n\r\n\r\n\r\n");
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202 fprintf(stderr, "Number of hashtable lookups: %ld\r\n", hash_count_lookup);
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203 fprintf(stderr, "Number of perturb loops: %ld\r\n", hash_count_perturb);
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204 fprintf(stderr, "Percentage of perturb loops: %ld%%\r\n",
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205 hash_count_perturb * 100 / hash_count_lookup);
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206 #endif
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207 }
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208
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209 /*
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210 * Add item with key "key" to hashtable "ht".
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211 * Returns FAIL when out of memory or the key is already present.
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212 */
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213 int
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214 hash_add(ht, key)
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215 hashtab_T *ht;
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216 char_u *key;
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217 {
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218 hash_T hash = hash_hash(key);
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219 hashitem_T *hi;
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220
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221 hi = hash_lookup(ht, key, hash);
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222 if (!HASHITEM_EMPTY(hi))
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223 {
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224 EMSG2(_(e_intern2), "hash_add()");
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225 return FAIL;
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226 }
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227 return hash_add_item(ht, hi, key, hash);
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228 }
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229
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230 /*
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231 * Add item "hi" with "key" to hashtable "ht". "key" must not be NULL and
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232 * "hi" must have been obtained with hash_lookup() and point to an empty item.
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233 * "hi" is invalid after this!
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234 * Returns OK or FAIL (out of memory).
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235 */
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236 int
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237 hash_add_item(ht, hi, key, hash)
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238 hashtab_T *ht;
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239 hashitem_T *hi;
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240 char_u *key;
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241 hash_T hash;
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242 {
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243 /* If resizing failed before and it fails again we can't add an item. */
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244 if (ht->ht_error && hash_may_resize(ht, 0) == FAIL)
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245 return FAIL;
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246
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247 ++ht->ht_used;
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248 if (hi->hi_key == NULL)
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249 ++ht->ht_filled;
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250 hi->hi_key = key;
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251 hi->hi_hash = hash;
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252
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253 /* When the space gets low may resize the array. */
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254 return hash_may_resize(ht, 0);
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255 }
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256
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257 #if 0 /* not used */
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258 /*
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259 * Overwrite hashtable item "hi" with "key". "hi" must point to the item that
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260 * is to be overwritten. Thus the number of items in the hashtable doesn't
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261 * change.
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262 * Although the key must be identical, the pointer may be different, thus it's
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263 * set anyway (the key is part of an item with that key).
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264 * The caller must take care of freeing the old item.
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265 * "hi" is invalid after this!
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266 */
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267 void
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268 hash_set(hi, key)
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269 hashitem_T *hi;
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270 char_u *key;
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271 {
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272 hi->hi_key = key;
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273 }
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274 #endif
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275
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276 /*
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277 * Remove item "hi" from hashtable "ht". "hi" must have been obtained with
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278 * hash_lookup().
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279 * The caller must take care of freeing the item itself.
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280 */
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281 void
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282 hash_remove(ht, hi)
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283 hashtab_T *ht;
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284 hashitem_T *hi;
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285 {
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286 --ht->ht_used;
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287 hi->hi_key = HI_KEY_REMOVED;
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288 hash_may_resize(ht, 0);
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289 }
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290
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291 /*
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292 * Lock a hashtable: prevent that ht_array changes.
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293 * Don't use this when items are to be added!
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294 * Must call hash_unlock() later.
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295 */
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296 void
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297 hash_lock(ht)
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298 hashtab_T *ht;
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299 {
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300 ++ht->ht_locked;
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301 }
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302
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303 #if 0 /* currently not used */
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304 /*
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305 * Lock a hashtable at the specified number of entries.
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306 * Caller must make sure no more than "size" entries will be added.
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307 * Must call hash_unlock() later.
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308 */
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309 void
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310 hash_lock_size(ht, size)
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311 hashtab_T *ht;
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312 int size;
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313 {
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314 (void)hash_may_resize(ht, size);
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315 ++ht->ht_locked;
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316 }
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317 #endif
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318
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319 /*
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320 * Unlock a hashtable: allow ht_array changes again.
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321 * Table will be resized (shrink) when necessary.
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322 * This must balance a call to hash_lock().
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323 */
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324 void
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325 hash_unlock(ht)
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326 hashtab_T *ht;
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327 {
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328 --ht->ht_locked;
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329 (void)hash_may_resize(ht, 0);
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330 }
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331
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332 /*
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333 * Shrink a hashtable when there is too much empty space.
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334 * Grow a hashtable when there is not enough empty space.
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335 * Returns OK or FAIL (out of memory).
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336 */
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337 static int
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338 hash_may_resize(ht, minitems)
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339 hashtab_T *ht;
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340 int minitems; /* minimal number of items */
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341 {
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342 hashitem_T temparray[HT_INIT_SIZE];
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343 hashitem_T *oldarray, *newarray;
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344 hashitem_T *olditem, *newitem;
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345 int newi;
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346 int todo;
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347 long_u oldsize, newsize;
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348 long_u minsize;
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349 long_u newmask;
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350 hash_T perturb;
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351
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352 /* Don't resize a locked table. */
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353 if (ht->ht_locked > 0)
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354 return OK;
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355
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356 #ifdef HT_DEBUG
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357 if (ht->ht_used > ht->ht_filled)
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358 EMSG("hash_may_resize(): more used than filled");
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359 if (ht->ht_filled >= ht->ht_mask + 1)
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360 EMSG("hash_may_resize(): table completely filled");
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361 #endif
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362
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363 if (minitems == 0)
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364 {
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365 /* Return quickly for small tables with at least two NULL items. NULL
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366 * items are required for the lookup to decide a key isn't there. */
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367 if (ht->ht_filled < HT_INIT_SIZE - 1
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368 && ht->ht_array == ht->ht_smallarray)
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369 return OK;
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370
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371 /*
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372 * Grow or refill the array when it's more than 2/3 full (including
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373 * removed items, so that they get cleaned up).
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374 * Shrink the array when it's less than 1/5 full. When growing it is
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375 * at least 1/4 full (avoids repeated grow-shrink operations)
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376 */
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377 oldsize = ht->ht_mask + 1;
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378 if (ht->ht_filled * 3 < oldsize * 2 && ht->ht_used > oldsize / 5)
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379 return OK;
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380
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381 if (ht->ht_used > 1000)
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382 minsize = ht->ht_used * 2; /* it's big, don't make too much room */
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383 else
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384 minsize = ht->ht_used * 4; /* make plenty of room */
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385 }
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386 else
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387 {
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388 /* Use specified size. */
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389 if ((long_u)minitems < ht->ht_used) /* just in case... */
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835
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390 minitems = (int)ht->ht_used;
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799
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391 minsize = minitems * 3 / 2; /* array is up to 2/3 full */
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392 }
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393
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394 newsize = HT_INIT_SIZE;
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395 while (newsize < minsize)
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396 {
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397 newsize <<= 1; /* make sure it's always a power of 2 */
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398 if (newsize == 0)
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399 return FAIL; /* overflow */
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400 }
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401
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402 if (newsize == HT_INIT_SIZE)
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403 {
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404 /* Use the small array inside the hashdict structure. */
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405 newarray = ht->ht_smallarray;
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406 if (ht->ht_array == newarray)
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407 {
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408 /* Moving from ht_smallarray to ht_smallarray! Happens when there
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409 * are many removed items. Copy the items to be able to clean up
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410 * removed items. */
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411 mch_memmove(temparray, newarray, sizeof(temparray));
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412 oldarray = temparray;
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413 }
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414 else
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415 oldarray = ht->ht_array;
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416 }
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417 else
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418 {
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419 /* Allocate an array. */
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420 newarray = (hashitem_T *)alloc((unsigned)
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421 (sizeof(hashitem_T) * newsize));
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422 if (newarray == NULL)
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423 {
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424 /* Out of memory. When there are NULL items still return OK.
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425 * Otherwise set ht_error, because lookup may result in a hang if
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426 * we add another item. */
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427 if (ht->ht_filled < ht->ht_mask)
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428 return OK;
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429 ht->ht_error = TRUE;
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430 return FAIL;
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431 }
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432 oldarray = ht->ht_array;
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433 }
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434 vim_memset(newarray, 0, (size_t)(sizeof(hashitem_T) * newsize));
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435
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436 /*
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437 * Move all the items from the old array to the new one, placing them in
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438 * the right spot. The new array won't have any removed items, thus this
|
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439 * is also a cleanup action.
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440 */
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|
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441 newmask = newsize - 1;
|
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835
|
442 todo = (int)ht->ht_used;
|
|
799
|
443 for (olditem = oldarray; todo > 0; ++olditem)
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444 if (!HASHITEM_EMPTY(olditem))
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|
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445 {
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|
|
446 /*
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|
|
447 * The algorithm to find the spot to add the item is identical to
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|
|
448 * the algorithm to find an item in hash_lookup(). But we only
|
|
|
449 * need to search for a NULL key, thus it's simpler.
|
|
|
450 */
|
|
835
|
451 newi = (int)(olditem->hi_hash & newmask);
|
|
799
|
452 newitem = &newarray[newi];
|
|
|
453
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|
|
454 if (newitem->hi_key != NULL)
|
|
|
455 for (perturb = olditem->hi_hash; ; perturb >>= PERTURB_SHIFT)
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|
|
456 {
|
|
835
|
457 newi = (int)((newi << 2) + newi + perturb + 1);
|
|
799
|
458 newitem = &newarray[newi & newmask];
|
|
|
459 if (newitem->hi_key == NULL)
|
|
|
460 break;
|
|
|
461 }
|
|
|
462 *newitem = *olditem;
|
|
|
463 --todo;
|
|
|
464 }
|
|
|
465
|
|
|
466 if (ht->ht_array != ht->ht_smallarray)
|
|
|
467 vim_free(ht->ht_array);
|
|
|
468 ht->ht_array = newarray;
|
|
|
469 ht->ht_mask = newmask;
|
|
|
470 ht->ht_filled = ht->ht_used;
|
|
|
471 ht->ht_error = FALSE;
|
|
|
472
|
|
|
473 return OK;
|
|
|
474 }
|
|
|
475
|
|
|
476 /*
|
|
|
477 * Get the hash number for a key.
|
|
|
478 * If you think you know a better hash function: Compile with HT_DEBUG set and
|
|
|
479 * run a script that uses hashtables a lot. Vim will then print statistics
|
|
|
480 * when exiting. Try that with the current hash algorithm and yours. The
|
|
|
481 * lower the percentage the better.
|
|
|
482 */
|
|
|
483 hash_T
|
|
|
484 hash_hash(key)
|
|
|
485 char_u *key;
|
|
|
486 {
|
|
|
487 hash_T hash;
|
|
|
488 char_u *p;
|
|
|
489
|
|
|
490 if ((hash = *key) == 0)
|
|
|
491 return (hash_T)0; /* Empty keys are not allowed, but we don't
|
|
|
492 want to crash if we get one. */
|
|
|
493 p = key + 1;
|
|
|
494
|
|
|
495 #if 0
|
|
|
496 /* ElfHash algorithm, which is supposed to have an even distribution.
|
|
|
497 * Suggested by Charles Campbell. */
|
|
|
498 hash_T g;
|
|
|
499
|
|
|
500 while (*p != NUL)
|
|
|
501 {
|
|
|
502 hash = (hash << 4) + *p++; /* clear low 4 bits of hash, add char */
|
|
|
503 g = hash & 0xf0000000L; /* g has high 4 bits of hash only */
|
|
|
504 if (g != 0)
|
|
|
505 hash ^= g >> 24; /* xor g's high 4 bits into hash */
|
|
|
506 }
|
|
|
507 #else
|
|
|
508
|
|
|
509 /* A simplistic algorithm that appears to do very well.
|
|
|
510 * Suggested by George Reilly. */
|
|
|
511 while (*p != NUL)
|
|
|
512 hash = hash * 101 + *p++;
|
|
|
513 #endif
|
|
|
514
|
|
|
515 return hash;
|
|
|
516 }
|
|
|
517
|
|
|
518 #endif
|
