Line data    Source code

       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * kwlookup.c
       4             :  *    Key word lookup for PostgreSQL
       5             :  *
       6             :  *
       7             :  * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
       8             :  * Portions Copyright (c) 1994, Regents of the University of California
       9             :  *
      10             :  *
      11             :  * IDENTIFICATION
      12             :  *    src/common/kwlookup.c
      13             :  *
      14             :  *-------------------------------------------------------------------------
      15             :  */
      16             : #include "c.h"
      17             : 
      18             : #include "common/kwlookup.h"
      19             : 
      20             : 
      21             : /*
      22             :  * ScanKeywordLookup - see if a given word is a keyword
      23             :  *
      24             :  * The list of keywords to be matched against is passed as a ScanKeywordList.
      25             :  *
      26             :  * Returns the keyword number (0..N-1) of the keyword, or -1 if no match.
      27             :  * Callers typically use the keyword number to index into information
      28             :  * arrays, but that is no concern of this code.
      29             :  *
      30             :  * The match is done case-insensitively.  Note that we deliberately use a
      31             :  * dumbed-down case conversion that will only translate 'A'-'Z' into 'a'-'z',
      32             :  * even if we are in a locale where tolower() would produce more or different
      33             :  * translations.  This is to conform to the SQL99 spec, which says that
      34             :  * keywords are to be matched in this way even though non-keyword identifiers
      35             :  * receive a different case-normalization mapping.
      36             :  */
      37             : int
      38    13264060 : ScanKeywordLookup(const char *str,
      39             :                   const ScanKeywordList *keywords)
      40             : {
      41             :     size_t      len;
      42             :     int         h;
      43             :     const char *kw;
      44             : 
      45             :     /*
      46             :      * Reject immediately if too long to be any keyword.  This saves useless
      47             :      * hashing and downcasing work on long strings.
      48             :      */
      49    13264060 :     len = strlen(str);
      50    13264060 :     if (len > keywords->max_kw_len)
      51      458358 :         return -1;
      52             : 
      53             :     /*
      54             :      * Compute the hash function.  We assume it was generated to produce
      55             :      * case-insensitive results.  Since it's a perfect hash, we need only
      56             :      * match to the specific keyword it identifies.
      57             :      */
      58    12805702 :     h = keywords->hash(str, len);
      59             : 
      60             :     /* An out-of-range result implies no match */
      61    12805702 :     if (h < 0 || h >= keywords->num_keywords)
      62     5445810 :         return -1;
      63             : 
      64             :     /*
      65             :      * Compare character-by-character to see if we have a match, applying an
      66             :      * ASCII-only downcasing to the input characters.  We must not use
      67             :      * tolower() since it may produce the wrong translation in some locales
      68             :      * (eg, Turkish).
      69             :      */
      70     7359892 :     kw = GetScanKeyword(h, keywords);
      71    31470642 :     while (*str != '\0')
      72             :     {
      73    26150486 :         char        ch = *str++;
      74             : 
      75    26150486 :         if (ch >= 'A' && ch <= 'Z')
      76    16496830 :             ch += 'a' - 'A';
      77    26150486 :         if (ch != *kw++)
      78     2039736 :             return -1;
      79             :     }
      80     5320156 :     if (*kw != '\0')
      81           0 :         return -1;
      82             : 
      83             :     /* Success! */
      84     5320156 :     return h;
      85             : }