Mysql源码学习——打造专属语法(7)

        (lip->m_thd->variables.sql_mode & MODE_HIGH_NOT_PRECEDENCE))

      return NOT2_SYM;

    if ((symbol->tok == OR_OR_SYM) &&

    !(lip->m_thd->variables.sql_mode & MODE_PIPES_AS_CONCAT))

      return OR2_SYM;

    return symbol->tok;

  }

  return 0;

}

static SYMBOL *get_hash_symbol(const char *s,

                               unsigned int len,bool function)

{

  register uchar *hash_map;

  register const char *cur_str= s;

  if (len == 0) {

    DBUG_PRINT("warning", ("get_hash_symbol() received a request for a zero-length symbol, which is probably a mistake."));

? 

    return(NULL);

  }

  if (function){

    if (len>sql_functions_max_len) return 0;

    hash_map= sql_functions_map;

    register uint32 cur_struct= uint4korr(hash_map+((len-1)*4));

    for (;;){

      register uchar first_char= (uchar)cur_struct;

      if (first_char == 0)

      {

        register int16 ires= (int16)(cur_struct>>16);

        if (ires==array_elements(symbols)) return 0;

        register SYMBOL *res;

        if (ires>=0)

          res= symbols+ires;

        else

          res= sql_functions-ires-1;

          register uint count= (uint) (cur_str - s);

        return lex_casecmp(cur_str,res->name+count,len-count) ? 0 : res;

      }

      register uchar cur_char= (uchar)to_upper_lex[(uchar)*cur_str];

      if (cur_char<first_char) return 0;

      cur_struct>>=8;

      if (cur_char>(uchar)cur_struct) return 0;

      cur_struct>>=8;

      cur_struct= uint4korr(hash_map+

                        (((uint16)cur_struct + cur_char - first_char)*4));