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kwlookup.c
/*-------------------------------------------------------------------------
 *
 * kwlookup.c
 *      lexical token lookup for key words in PostgreSQL
 *
 * NB - this file is also used by ECPG and several frontend programs in
 * src/bin/ including pg_dump and psql
 *
 * Note that this file expects that the ScanKeywords array is defined
 * and that LastScanKeyword points to its element one past the last.
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *      $PostgreSQL: pgsql/src/backend/parser/kwlookup.c,v 2.2 2009/03/08 16:53:30 alvherre Exp $
 *
 *-------------------------------------------------------------------------
 */

/* use c.h so this can be built as either frontend or backend */
#include "c.h"

#include <ctype.h>

#include "parser/keywords.h"

/*
 * ScanKeywordLookup - see if a given word is a keyword
 *
 * Returns a pointer to the ScanKeyword table entry, or NULL if no match.
 *
 * 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.
 */
const ScanKeyword *
ScanKeywordLookup(const char *text)
{
      int               len,
                        i;
      char        word[NAMEDATALEN];
      const ScanKeyword *low;
      const ScanKeyword *high;

      len = strlen(text);
      /* We assume all keywords are shorter than NAMEDATALEN. */
      if (len >= NAMEDATALEN)
            return NULL;

      /*
       * Apply an ASCII-only downcasing.  We must not use tolower() since it may
       * produce the wrong translation in some locales (eg, Turkish).
       */
      for (i = 0; i < len; i++)
      {
            char        ch = text[i];

            if (ch >= 'A' && ch <= 'Z')
                  ch += 'a' - 'A';
            word[i] = ch;
      }
      word[len] = '\0';

      /*
       * Now do a binary search using plain strcmp() comparison.
       */
      low = &ScanKeywords[0];
      high = LastScanKeyword - 1;
      while (low <= high)
      {
            const ScanKeyword *middle;
            int               difference;

            middle = low + (high - low) / 2;
            difference = strcmp(middle->name, word);
            if (difference == 0)
                  return middle;
            else if (difference < 0)
                  low = middle + 1;
            else
                  high = middle - 1;
      }

      return NULL;
}

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