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1 /* Hash tables.
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2 Copyright (C) 2000, 2001, 2003, 2004, 2008, 2009
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3 Free Software Foundation, Inc.
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4
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5 This program is free software; you can redistribute it and/or modify it
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6 under the terms of the GNU General Public License as published by the
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7 Free Software Foundation; either version 3, or (at your option) any
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8 later version.
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9
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10 This program is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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13 GNU General Public License for more details.
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14
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15 You should have received a copy of the GNU General Public License
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16 along with this program; see the file COPYING3. If not see
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17 <http://www.gnu.org/licenses/>.
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18
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19 In other words, you are welcome to use, share and improve this program.
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20 You are forbidden to forbid anyone else to use, share and improve
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21 what you give them. Help stamp out software-hoarding! */
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22
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23 #include "config.h"
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24 #include "system.h"
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25 #include "symtab.h"
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26
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27 /* The code below is a specialization of Vladimir Makarov's expandable
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28 hash tables (see libiberty/hashtab.c). The abstraction penalty was
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29 too high to continue using the generic form. This code knows
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30 intrinsically how to calculate a hash value, and how to compare an
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31 existing entry with a potential new one. */
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32
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33 static unsigned int calc_hash (const unsigned char *, size_t);
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34 static void ht_expand (hash_table *);
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35 static double approx_sqrt (double);
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36
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37 /* A deleted entry. */
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38 #define DELETED ((hashnode) -1)
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39
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40 /* Calculate the hash of the string STR of length LEN. */
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41
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42 static unsigned int
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43 calc_hash (const unsigned char *str, size_t len)
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44 {
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45 size_t n = len;
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46 unsigned int r = 0;
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47
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48 while (n--)
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49 r = HT_HASHSTEP (r, *str++);
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50
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51 return HT_HASHFINISH (r, len);
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52 }
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53
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54 /* Initialize an identifier hashtable. */
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55
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56 hash_table *
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57 ht_create (unsigned int order)
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58 {
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59 unsigned int nslots = 1 << order;
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60 hash_table *table;
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61
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62 table = XCNEW (hash_table);
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63
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64 /* Strings need no alignment. */
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65 _obstack_begin (&table->stack, 0, 0,
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66 (void *(*) (long)) xmalloc,
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67 (void (*) (void *)) free);
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68
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69 obstack_alignment_mask (&table->stack) = 0;
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70
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71 table->entries = XCNEWVEC (hashnode, nslots);
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72 table->entries_owned = true;
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73 table->nslots = nslots;
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74 return table;
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75 }
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76
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77 /* Frees all memory associated with a hash table. */
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78
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79 void
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80 ht_destroy (hash_table *table)
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81 {
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82 obstack_free (&table->stack, NULL);
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83 if (table->entries_owned)
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84 free (table->entries);
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85 free (table);
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86 }
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87
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88 /* Returns the hash entry for the a STR of length LEN. If that string
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89 already exists in the table, returns the existing entry. If the
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90 identifier hasn't been seen before, and INSERT is CPP_NO_INSERT,
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91 returns NULL. Otherwise insert and returns a new entry. A new
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92 string is allocated. */
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93 hashnode
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94 ht_lookup (hash_table *table, const unsigned char *str, size_t len,
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95 enum ht_lookup_option insert)
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96 {
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97 return ht_lookup_with_hash (table, str, len, calc_hash (str, len),
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98 insert);
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99 }
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100
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101 hashnode
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102 ht_lookup_with_hash (hash_table *table, const unsigned char *str,
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103 size_t len, unsigned int hash,
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104 enum ht_lookup_option insert)
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105 {
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106 unsigned int hash2;
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107 unsigned int index;
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108 unsigned int deleted_index = table->nslots;
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109 size_t sizemask;
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110 hashnode node;
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111
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112 sizemask = table->nslots - 1;
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113 index = hash & sizemask;
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114 table->searches++;
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115
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116 node = table->entries[index];
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117
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118 if (node != NULL)
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119 {
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120 if (node == DELETED)
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121 deleted_index = index;
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122 else if (node->hash_value == hash
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123 && HT_LEN (node) == (unsigned int) len
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124 && !memcmp (HT_STR (node), str, len))
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125 return node;
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126
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127 /* hash2 must be odd, so we're guaranteed to visit every possible
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128 location in the table during rehashing. */
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129 hash2 = ((hash * 17) & sizemask) | 1;
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130
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131 for (;;)
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132 {
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133 table->collisions++;
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134 index = (index + hash2) & sizemask;
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135 node = table->entries[index];
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136 if (node == NULL)
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137 break;
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138
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139 if (node == DELETED)
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140 {
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141 if (deleted_index != table->nslots)
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142 deleted_index = index;
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143 }
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144 else if (node->hash_value == hash
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145 && HT_LEN (node) == (unsigned int) len
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146 && !memcmp (HT_STR (node), str, len))
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147 return node;
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148 }
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149 }
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150
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151 if (insert == HT_NO_INSERT)
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152 return NULL;
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153
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154 /* We prefer to overwrite the first deleted slot we saw. */
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155 if (deleted_index != table->nslots)
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156 index = deleted_index;
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157
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158 node = (*table->alloc_node) (table);
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159 table->entries[index] = node;
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160
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161 HT_LEN (node) = (unsigned int) len;
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162 node->hash_value = hash;
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163
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164 if (table->alloc_subobject)
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165 {
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166 char *chars = table->alloc_subobject (len + 1);
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167 memcpy (chars, str, len);
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168 chars[len] = '\0';
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169 HT_STR (node) = (const unsigned char *) chars;
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170 }
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171 else
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172 HT_STR (node) = (const unsigned char *) obstack_copy0 (&table->stack,
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173 str, len);
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174
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175 if (++table->nelements * 4 >= table->nslots * 3)
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176 /* Must expand the string table. */
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177 ht_expand (table);
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178
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179 return node;
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180 }
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181
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182 /* Double the size of a hash table, re-hashing existing entries. */
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183
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184 static void
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185 ht_expand (hash_table *table)
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186 {
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187 hashnode *nentries, *p, *limit;
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188 unsigned int size, sizemask;
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189
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190 size = table->nslots * 2;
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191 nentries = XCNEWVEC (hashnode, size);
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192 sizemask = size - 1;
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193
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194 p = table->entries;
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195 limit = p + table->nslots;
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196 do
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197 if (*p && *p != DELETED)
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198 {
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199 unsigned int index, hash, hash2;
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200
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201 hash = (*p)->hash_value;
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202 index = hash & sizemask;
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203
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204 if (nentries[index])
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205 {
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206 hash2 = ((hash * 17) & sizemask) | 1;
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207 do
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208 {
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209 index = (index + hash2) & sizemask;
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210 }
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211 while (nentries[index]);
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212 }
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213 nentries[index] = *p;
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214 }
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215 while (++p < limit);
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216
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217 if (table->entries_owned)
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218 free (table->entries);
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219 table->entries_owned = true;
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220 table->entries = nentries;
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221 table->nslots = size;
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222 }
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223
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224 /* For all nodes in TABLE, callback CB with parameters TABLE->PFILE,
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225 the node, and V. */
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226 void
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227 ht_forall (hash_table *table, ht_cb cb, const void *v)
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228 {
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229 hashnode *p, *limit;
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230
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231 p = table->entries;
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232 limit = p + table->nslots;
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233 do
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234 if (*p && *p != DELETED)
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235 {
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236 if ((*cb) (table->pfile, *p, v) == 0)
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237 break;
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238 }
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239 while (++p < limit);
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240 }
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241
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242 /* Like ht_forall, but a nonzero return from the callback means that
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243 the entry should be removed from the table. */
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244 void
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245 ht_purge (hash_table *table, ht_cb cb, const void *v)
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246 {
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247 hashnode *p, *limit;
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248
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249 p = table->entries;
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250 limit = p + table->nslots;
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251 do
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252 if (*p && *p != DELETED)
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253 {
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254 if ((*cb) (table->pfile, *p, v))
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255 *p = DELETED;
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256 }
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257 while (++p < limit);
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258 }
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259
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260 /* Restore the hash table. */
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261 void
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262 ht_load (hash_table *ht, hashnode *entries,
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263 unsigned int nslots, unsigned int nelements,
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264 bool own)
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265 {
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266 if (ht->entries_owned)
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267 free (ht->entries);
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268 ht->entries = entries;
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269 ht->nslots = nslots;
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270 ht->nelements = nelements;
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271 ht->entries_owned = own;
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272 }
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273
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274 /* Dump allocation statistics to stderr. */
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275
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276 void
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277 ht_dump_statistics (hash_table *table)
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278 {
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279 size_t nelts, nids, overhead, headers;
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280 size_t total_bytes, longest, deleted = 0;
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281 double sum_of_squares, exp_len, exp_len2, exp2_len;
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282 hashnode *p, *limit;
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283
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284 #define SCALE(x) ((unsigned long) ((x) < 1024*10 \
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285 ? (x) \
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286 : ((x) < 1024*1024*10 \
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287 ? (x) / 1024 \
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288 : (x) / (1024*1024))))
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289 #define LABEL(x) ((x) < 1024*10 ? ' ' : ((x) < 1024*1024*10 ? 'k' : 'M'))
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290
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291 total_bytes = longest = sum_of_squares = nids = 0;
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292 p = table->entries;
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293 limit = p + table->nslots;
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294 do
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295 if (*p == DELETED)
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296 ++deleted;
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297 else if (*p)
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298 {
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299 size_t n = HT_LEN (*p);
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300
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301 total_bytes += n;
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302 sum_of_squares += (double) n * n;
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303 if (n > longest)
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304 longest = n;
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305 nids++;
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306 }
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307 while (++p < limit);
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308
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309 nelts = table->nelements;
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310 overhead = obstack_memory_used (&table->stack) - total_bytes;
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311 headers = table->nslots * sizeof (hashnode);
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312
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313 fprintf (stderr, "\nString pool\nentries\t\t%lu\n",
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314 (unsigned long) nelts);
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315 fprintf (stderr, "identifiers\t%lu (%.2f%%)\n",
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316 (unsigned long) nids, nids * 100.0 / nelts);
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317 fprintf (stderr, "slots\t\t%lu\n",
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318 (unsigned long) table->nslots);
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319 fprintf (stderr, "deleted\t\t%lu\n",
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320 (unsigned long) deleted);
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321 fprintf (stderr, "bytes\t\t%lu%c (%lu%c overhead)\n",
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322 SCALE (total_bytes), LABEL (total_bytes),
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323 SCALE (overhead), LABEL (overhead));
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324 fprintf (stderr, "table size\t%lu%c\n",
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325 SCALE (headers), LABEL (headers));
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326
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327 exp_len = (double)total_bytes / (double)nelts;
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328 exp2_len = exp_len * exp_len;
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329 exp_len2 = (double) sum_of_squares / (double) nelts;
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330
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331 fprintf (stderr, "coll/search\t%.4f\n",
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332 (double) table->collisions / (double) table->searches);
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333 fprintf (stderr, "ins/search\t%.4f\n",
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334 (double) nelts / (double) table->searches);
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335 fprintf (stderr, "avg. entry\t%.2f bytes (+/- %.2f)\n",
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336 exp_len, approx_sqrt (exp_len2 - exp2_len));
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337 fprintf (stderr, "longest entry\t%lu\n",
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338 (unsigned long) longest);
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339 #undef SCALE
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340 #undef LABEL
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341 }
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342
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343 /* Return the approximate positive square root of a number N. This is for
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344 statistical reports, not code generation. */
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345 static double
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346 approx_sqrt (double x)
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347 {
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348 double s, d;
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349
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350 if (x < 0)
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351 abort ();
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352 if (x == 0)
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353 return 0;
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354
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355 s = x;
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356 do
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357 {
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358 d = (s * s - x) / (2 * s);
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359 s -= d;
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360 }
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361 while (d > .0001);
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362 return s;
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363 }
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