src/common/kwlookup.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * kwlookup.c
   4  *        Key word lookup for PostgreSQL
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2023, 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 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         len = strlen(str);
  50         if (len > keywords->max_kw_len)
  51                 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         h = keywords->hash(str, len);
  59
  60         /* An out-of-range result implies no match */
  61         if (h < 0 || h >= keywords->num_keywords)
  62                 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         kw = GetScanKeyword(h, keywords);
  71         while (*str != '\0')
  72         {
  73                 char            ch = *str++;
  74
  75                 if (ch >= 'A' && ch <= 'Z')
  76                         ch += 'a' - 'A';
  77                 if (ch != *kw++)
  78                         return -1;
  79         }
  80         if (*kw != '\0')
  81                 return -1;
  82
  83         /* Success! */
  84         return h;
  85 }