PostgreSQL Source Code  git master
kwlookup.c
Go to the documentation of this file.
1 /*-------------------------------------------------------------------------
2  *
3  * kwlookup.c
4  * Key word lookup for PostgreSQL
5  *
6  *
7  * Portions Copyright (c) 1996-2019, 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 }
static const char * GetScanKeyword(int n, const ScanKeywordList *keywords)
Definition: kwlookup.h:39
ScanKeywordHashFunc hash
Definition: kwlookup.h:29
int num_keywords
Definition: kwlookup.h:30
int ScanKeywordLookup(const char *str, const ScanKeywordList *keywords)
Definition: kwlookup.c:38