1 | /* findkey.c - The routine that finds a key entry in the file. */
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2 |
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3 | /* This file is part of GDBM, the GNU data base manager, by Philip A. Nelson.
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4 | Copyright (C) 1990, 1991, 1993 Free Software Foundation, Inc.
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5 |
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6 | GDBM is free software; you can redistribute it and/or modify
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7 | it under the terms of the GNU General Public License as published by
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8 | the Free Software Foundation; either version 2, or (at your option)
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9 | any later version.
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10 |
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11 | GDBM is distributed in the hope that it will be useful,
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12 | but WITHOUT ANY WARRANTY; without even the implied warranty of
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13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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14 | GNU General Public License for more details.
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15 |
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16 | You should have received a copy of the GNU General Public License
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17 | along with GDBM; see the file COPYING. If not, write to
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18 | the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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19 |
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20 | You may contact the author by:
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21 | e-mail: [email protected]
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22 | us-mail: Philip A. Nelson
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23 | Computer Science Department
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24 | Western Washington University
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25 | Bellingham, WA 98226
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26 |
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27 | *************************************************************************/
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28 |
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29 |
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30 | /* include system configuration before all else. */
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31 | #include "autoconf.h"
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32 |
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33 | #include "gdbmdefs.h"
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34 |
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35 |
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36 | /* Read the data found in bucket entry ELEM_LOC in file DBF and
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37 | return a pointer to it. Also, cache the read value. */
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38 |
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39 | char *
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40 | _gdbm_read_entry (dbf, elem_loc)
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41 | gdbm_file_info *dbf;
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42 | int elem_loc;
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43 | {
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44 | int num_bytes; /* For seeking and reading. */
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45 | int key_size;
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46 | int data_size;
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47 | off_t file_pos;
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48 | data_cache_elem *data_ca;
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49 |
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50 | /* Is it already in the cache? */
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51 | if (dbf->cache_entry->ca_data.elem_loc == elem_loc)
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52 | return dbf->cache_entry->ca_data.dptr;
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53 |
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54 | /* Set sizes and pointers. */
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55 | key_size = dbf->bucket->h_table[elem_loc].key_size;
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56 | data_size = dbf->bucket->h_table[elem_loc].data_size;
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57 | data_ca = &dbf->cache_entry->ca_data;
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58 |
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59 | /* Set up the cache. */
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60 | if (data_ca->dptr != NULL) free (data_ca->dptr);
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61 | data_ca->key_size = key_size;
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62 | data_ca->data_size = data_size;
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63 | data_ca->elem_loc = elem_loc;
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64 | data_ca->hash_val = dbf->bucket->h_table[elem_loc].hash_value;
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65 | if (key_size+data_size == 0)
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66 | data_ca->dptr = (char *) malloc (1);
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67 | else
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68 | data_ca->dptr = (char *) malloc (key_size+data_size);
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69 | if (data_ca->dptr == NULL) _gdbm_fatal (dbf, "malloc error");
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70 |
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71 |
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72 | /* Read into the cache. */
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73 | file_pos = lseek (dbf->desc,
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74 | dbf->bucket->h_table[elem_loc].data_pointer, L_SET);
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75 | if (file_pos != dbf->bucket->h_table[elem_loc].data_pointer)
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76 | _gdbm_fatal (dbf, "lseek error");
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77 | num_bytes = read (dbf->desc, data_ca->dptr, key_size+data_size);
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78 | if (num_bytes != key_size+data_size) _gdbm_fatal (dbf, "read error");
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79 |
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80 | return data_ca->dptr;
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81 | }
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82 |
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83 |
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84 |
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85 | /* Find the KEY in the file and get ready to read the associated data. The
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86 | return value is the location in the current hash bucket of the KEY's
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87 | entry. If it is found, a pointer to the data and the key are returned
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88 | in DPTR. If it is not found, the value -1 is returned. Since find
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89 | key computes the hash value of key, that value */
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90 | int
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91 | _gdbm_findkey (dbf, key, dptr, new_hash_val)
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92 | gdbm_file_info *dbf;
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93 | datum key;
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94 | char **dptr;
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95 | int *new_hash_val; /* The new hash value. */
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96 | {
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97 | int bucket_hash_val; /* The hash value from the bucket. */
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98 | char *file_key; /* The complete key as stored in the file. */
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99 | int elem_loc; /* The location in the bucket. */
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100 | int home_loc; /* The home location in the bucket. */
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101 | int key_size; /* Size of the key on the file. */
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102 |
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103 | /* Compute hash value and load proper bucket. */
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104 | *new_hash_val = _gdbm_hash (key);
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105 | _gdbm_get_bucket (dbf, *new_hash_val>> (31-dbf->header->dir_bits));
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106 |
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107 | /* Is the element the last one found for this bucket? */
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108 | if (dbf->cache_entry->ca_data.elem_loc != -1
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109 | && *new_hash_val == dbf->cache_entry->ca_data.hash_val
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110 | && dbf->cache_entry->ca_data.key_size == key.dsize
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111 | && dbf->cache_entry->ca_data.dptr != NULL
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112 | && bcmp (dbf->cache_entry->ca_data.dptr, key.dptr, key.dsize) == 0)
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113 | {
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114 | /* This is it. Return the cache pointer. */
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115 | *dptr = dbf->cache_entry->ca_data.dptr+key.dsize;
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116 | return dbf->cache_entry->ca_data.elem_loc;
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117 | }
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118 |
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119 | /* It is not the cached value, search for element in the bucket. */
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120 | elem_loc = *new_hash_val % dbf->header->bucket_elems;
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121 | home_loc = elem_loc;
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122 | bucket_hash_val = dbf->bucket->h_table[elem_loc].hash_value;
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123 | while (bucket_hash_val != -1)
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124 | {
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125 | key_size = dbf->bucket->h_table[elem_loc].key_size;
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126 | if (bucket_hash_val != *new_hash_val
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127 | || key_size != key.dsize
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128 | || bcmp (dbf->bucket->h_table[elem_loc].key_start, key.dptr,
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129 | (SMALL < key_size ? SMALL : key_size)) != 0)
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130 | {
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131 | /* Current elem_loc is not the item, go to next item. */
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132 | elem_loc = (elem_loc + 1) % dbf->header->bucket_elems;
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133 | if (elem_loc == home_loc) return -1;
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134 | bucket_hash_val = dbf->bucket->h_table[elem_loc].hash_value;
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135 | }
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136 | else
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137 | {
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138 | /* This may be the one we want.
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139 | The only way to tell is to read it. */
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140 | file_key = _gdbm_read_entry (dbf, elem_loc);
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141 | if (bcmp (file_key, key.dptr, key_size) == 0)
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142 | {
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143 | /* This is the item. */
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144 | *dptr = file_key+key.dsize;
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145 | return elem_loc;
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146 | }
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147 | else
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148 | {
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149 | /* Not the item, try the next one. Return if not found. */
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150 | elem_loc = (elem_loc + 1) % dbf->header->bucket_elems;
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151 | if (elem_loc == home_loc) return -1;
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152 | bucket_hash_val = dbf->bucket->h_table[elem_loc].hash_value;
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153 | }
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154 | }
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155 | }
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156 |
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157 | /* If we get here, we never found the key. */
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158 | return -1;
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159 |
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160 | }
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