greenplumn kwlookup 源码
greenplumn kwlookup 代码
文件路径：/src/common/kwlookup.c
/*-------------------------------------------------------------------------
*
* kwlookup.c
* Key word lookup for PostgreSQL
*
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/common/kwlookup.c
*
*-------------------------------------------------------------------------
*/
#include "c.h"
#include "common/kwlookup.h"
/*
* ScanKeywordLookup - see if a given word is a keyword
*
* The list of keywords to be matched against is passed as a ScanKeywordList.
*
* Returns the keyword number (0..N-1) of the keyword, or -1 if no match.
* Callers typically use the keyword number to index into information
* arrays, but that is no concern of this code.
*
* The match is done case-insensitively. Note that we deliberately use a
* dumbed-down case conversion that will only translate 'A'-'Z' into 'a'-'z',
* even if we are in a locale where tolower() would produce more or different
* translations. This is to conform to the SQL99 spec, which says that
* keywords are to be matched in this way even though non-keyword identifiers
* receive a different case-normalization mapping.
*/
int
ScanKeywordLookup(const char *str,
const ScanKeywordList *keywords)
{
size_t len;
int h;
const char *kw;
/*
* Reject immediately if too long to be any keyword. This saves useless
* hashing and downcasing work on long strings.
*/
len = strlen(str);
if (len > keywords->max_kw_len)
return -1;
/*
* Compute the hash function. We assume it was generated to produce
* case-insensitive results. Since it's a perfect hash, we need only
* match to the specific keyword it identifies.
*/
h = keywords->hash(str, len);
/* An out-of-range result implies no match */
if (h < 0 || h >= keywords->num_keywords)
return -1;
/*
* Compare character-by-character to see if we have a match, applying an
* ASCII-only downcasing to the input characters. We must not use
* tolower() since it may produce the wrong translation in some locales
* (eg, Turkish).
*/
kw = GetScanKeyword(h, keywords);
while (*str != '\0')
{
char ch = *str++;
if (ch >= 'A' && ch <= 'Z')
ch += 'a' - 'A';
if (ch != *kw++)
return -1;
}
if (*kw != '\0')
return -1;
/* Success! */
return h;
}
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