xapian-core/common/keyword.cc

   1 /** @file keyword.cc
   2  * @brief Efficient keyword to enum lookup
   3  */
   4 /* Copyright (C) 2012 Olly Betts
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to
   8  * deal in the Software without restriction, including without limitation the
   9  * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
  10  * sell copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  19  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  21  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  22  * IN THE SOFTWARE.
  23  */
  24
  25 #include <config.h>
  26
  27 #include "keyword.h"
  28
  29 #include <string.h>
  30
  31 int
  32 keyword(const unsigned char * p, const char * s, size_t len)
  33 {
  34     if (len == 0 || len > p[0] || p[len] == 1)
  35         return -1;
  36     p = p + p[0] + p[len] + 3;
  37     const unsigned char * q = p + (len + 1) * (p[-2] + 1);
  38     /* Binary chop between p and q */
  39     size_t n = len + 1;
  40     size_t d = n * 2;
  41     while (p < q) {
  42         const unsigned char * m = p + (q - p) / d * n;
  43         int cmp = memcmp(s, m, len);
  44         if (cmp < 0) {
  45             q = m;
  46         } else if (cmp > 0) {
  47             p = m + n;
  48         } else {
  49             return m[-1];
  50         }
  51     }
  52     return -1;
  53 }