source: trunk/essentials/sys-devel/m4/src/symtab.c@ 3285

/* GNU m4 -- A simple macro processor

   Copyright (C) 1989, 1990, 1991, 1992, 1993, 1994, 2003, 2006 Free
   Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
   02110-1301  USA
*/

/* This file handles all the low level work around the symbol table.  The
   symbol table is a simple chained hash table.  Each symbol is described
   by a struct symbol, which is placed in the hash table based upon the
   symbol name.  Symbols that hash to the same entry in the table are
   kept on a list, sorted by name.  As a special case, to facilitate the
   "pushdef" and "popdef" builtins, a symbol can be several times in the
   symbol table, one for each definition.  Since the name is the same,
   all the entries for the symbol will be on the same list, and will
   also, because the list is sorted, be adjacent.  All the entries for a
   name are simply ordered on the list by age.  The current definition
   will then always be the first found.  */

#include "m4.h"
#include <limits.h>

#ifdef DEBUG_SYM
/* When evaluating hash table performance, this profiling code shows
   how many collisions were encountered.  */

struct profile
{
  int entry; /* Number of times lookup_symbol called with this mode.  */
  int comparisons; /* Number of times strcmp was called.  */
  int misses; /* Number of times strcmp did not return 0.  */
  long long bytes; /* Number of bytes compared.  */
};

static struct profile profiles[5];
static symbol_lookup current_mode;

/* On exit, show a profile of symbol table performance.  */
static void
show_profile (void)
{
  int i;
  for (i = 0; i < 5; i++)
    {
      fprintf(stderr, "m4: lookup mode %d called %d times, %d compares, "
              "%d misses, %lld bytes\n",
              i, profiles[i].entry, profiles[i].comparisons,
              profiles[i].misses, profiles[i].bytes);
    }
}

/* Like strcmp (S1, S2), but also track profiling statistics.  */
static int
profile_strcmp (const char *s1, const char *s2)
{
  int i = 1;
  int result;
  while (*s1 && *s1 == *s2)
    {
      s1++;
      s2++;
      i++;
    }
  result = (unsigned char) *s1 - (unsigned char) *s2;
  profiles[current_mode].comparisons++;
  if (result != 0)
    profiles[current_mode].misses++;
  profiles[current_mode].bytes += i;
  return result;
}

# define strcmp profile_strcmp
#endif /* DEBUG_SYM */



/*----------------------------------------------------------------------.
| Initialise the symbol table, by allocating the necessary storage, and |
| zeroing all the entries.                                              |
`----------------------------------------------------------------------*/

/* Pointer to symbol table.  */
symbol **symtab;

void
symtab_init (void)
{
  size_t i;
  symbol **s;

  s = symtab = (symbol **) xnmalloc (hash_table_size, sizeof (symbol *));

  for (i = 0; i < hash_table_size; i++)
    s[i] = NULL;

#ifdef DEBUG_SYM
  {
    int e = atexit(show_profile);
    if (e != 0)
      M4ERROR ((warning_status, 0,
                "INTERNAL ERROR: unable to show symtab profile"));
  }
#endif /* DEBUG_SYM */
}

/*--------------------------------------------------.
| Return a hashvalue for a string, from GNU-emacs.  |
`--------------------------------------------------*/

static size_t
hash (const char *s)
{
  register size_t val = 0;

  register const char *ptr = s;
  register char ch;

  while ((ch = *ptr++) != '\0')
    val = (val << 7) + (val >> (sizeof (val) * CHAR_BIT - 7)) + ch;
  return val;
}

/*--------------------------------------------.
| Free all storage associated with a symbol.  |
`--------------------------------------------*/

void
free_symbol (symbol *sym)
{
  if (SYMBOL_PENDING_EXPANSIONS (sym) > 0)
    SYMBOL_DELETED (sym) = true;
  else
    {
      free (SYMBOL_NAME (sym));
      if (SYMBOL_TYPE (sym) == TOKEN_TEXT)
        free (SYMBOL_TEXT (sym));
      free (sym);
    }
}

/*-------------------------------------------------------------------.
| Search in, and manipulation of the symbol table, are all done by   |
| lookup_symbol ().  It basically hashes NAME to a list in the       |
| symbol table, and searches this list for the first occurrence of a |
| symbol with the name.                                              |
|                                                                    |
| The MODE parameter determines what lookup_symbol () will do.  It   |
| can either just do a lookup, do a lookup and insert if not         |
| present, do an insertion even if the name is already in the list,  |
| delete the first occurrence of the name on the list, or delete all |
| occurrences of the name on the list.                               |
`-------------------------------------------------------------------*/

symbol *
lookup_symbol (const char *name, symbol_lookup mode)
{
  size_t h;
  int cmp = 1;
  symbol *sym, *prev;
  symbol **spp;

#if DEBUG_SYM
  current_mode = mode;
  profiles[mode].entry++;
#endif /* DEBUG_SYM */

  h = hash (name);
  sym = symtab[h % hash_table_size];

  for (prev = NULL; sym != NULL; prev = sym, sym = sym->next)
    {
      cmp = strcmp (SYMBOL_NAME (sym), name);
      if (cmp >= 0)
        break;
    }

  /* If just searching, return status of search.  */

  if (mode == SYMBOL_LOOKUP)
    return cmp == 0 ? sym : NULL;

  /* Symbol not found.  */

  spp = (prev != NULL) ?  &prev->next : &symtab[h % hash_table_size];

  switch (mode)
    {

    case SYMBOL_INSERT:

      /* If the name was found in the table, check whether it is still in
         use by a pending expansion.  If so, replace the table element with
         a new one; if not, just return the symbol.  If not found, just
         insert the name, and return the new symbol.  */

      if (cmp == 0 && sym != NULL)
        {
          if (SYMBOL_PENDING_EXPANSIONS (sym) > 0)
            {
              symbol *old = sym;
              SYMBOL_DELETED (old) = true;

              sym = (symbol *) xmalloc (sizeof (symbol));
              SYMBOL_TYPE (sym) = TOKEN_VOID;
              SYMBOL_TRACED (sym) = SYMBOL_TRACED (old);
              SYMBOL_NAME (sym) = xstrdup (name);
              SYMBOL_SHADOWED (sym) = false;
              SYMBOL_MACRO_ARGS (sym) = false;
              SYMBOL_BLIND_NO_ARGS (sym) = false;
              SYMBOL_DELETED (sym) = false;
              SYMBOL_PENDING_EXPANSIONS (sym) = 0;

              SYMBOL_NEXT (sym) = SYMBOL_NEXT (old);
              SYMBOL_NEXT (old) = NULL;
              (*spp) = sym;
            }
          return sym;