gconv_db.c

Newlib 嵌入式 C库 标准实现代码

/* Provide access to the collection of available transformation modules.
   Copyright (C) 1997,98,99,2000,2001 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <[e-mail]>, 1997.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <limits.h>
#include <search.h>
#include <stdlib.h>
#include <string.h>
#include <sys/param.h>
#include <dirent.h>

#include <dlfcn.h>
#include <gconv_int.h>
#include <gconv_charset.h>


/* Simple data structure for alias mapping.  We have two names, `from'
   and `to'.  */
void *__gconv_alias_db;

/* Array with available modules.  */
struct gconv_module *__gconv_modules_db;

/* We modify global data.   */
__LOCK_INIT(static, lock);


/* Function for searching alias.  */
int
__gconv_alias_compare (const void *p1, const void *p2)
{
  const struct gconv_alias *s1 = (const struct gconv_alias *) p1;
  const struct gconv_alias *s2 = (const struct gconv_alias *) p2;
  return strcmp (s1->fromname, s2->fromname);
}


/* To search for a derivation we create a list of intermediate steps.
   Each element contains a pointer to the element which precedes it
   in the derivation order.  */
struct derivation_step
{
  const char *result_set;
  size_t result_set_len;
  int cost_lo;
  int cost_hi;
  struct gconv_module *code;
  struct derivation_step *last;
  struct derivation_step *next;
};

#define NEW_STEP(result, hi, lo, module, last_mod) \
  ({ struct derivation_step *newp = alloca (sizeof (struct derivation_step)); \
     newp->result_set = result;						      \
     newp->result_set_len = strlen (result);				      \
     newp->cost_hi = hi;						      \
     newp->cost_lo = lo;						      \
     newp->code = module;						      \
     newp->last = last_mod;						      \
     newp->next = NULL;							      \
     newp; })


/* If a specific transformation is used more than once we should not need
   to start looking for it again.  Instead cache each successful result.  */
struct known_derivation
{
  const char *from;
  const char *to;
  struct __gconv_step *steps;
  size_t nsteps;
};

/* Compare function for database of found derivations.  */
static int
derivation_compare (const void *p1, const void *p2)
{
  const struct known_derivation *s1 = (const struct known_derivation *) p1;
  const struct known_derivation *s2 = (const struct known_derivation *) p2;
  int result;

  result = strcmp (s1->from, s2->from);
  if (result == 0)
    result = strcmp (s1->to, s2->to);
  return result;
}

/* The search tree for known derivations.  */
static void *known_derivations;

/* Look up whether given transformation was already requested before.  */
static int
internal_function
derivation_lookup (const char *fromset, const char *toset,
		   struct __gconv_step **handle, size_t *nsteps)
{
  struct known_derivation key = { fromset, toset, NULL, 0 };
  struct known_derivation **result;

  result = tfind (&key, &known_derivations, derivation_compare);

  if (result == NULL)
    return __GCONV_NOCONV;

  *handle = (*result)->steps;
  *nsteps = (*result)->nsteps;

  /* Please note that we return GCONV_OK even if the last search for
     this transformation was unsuccessful.  */
  return __GCONV_OK;
}

/* Add new derivation to list of known ones.  */
static void
internal_function
add_derivation (const char *fromset, const char *toset,
		struct __gconv_step *handle, size_t nsteps)
{
  struct known_derivation *new_deriv;
  size_t fromset_len = strlen (fromset) + 1;
  size_t toset_len = strlen (toset) + 1;

  new_deriv = (struct known_derivation *)
    malloc (sizeof (struct known_derivation) + fromset_len + toset_len);
  if (new_deriv != NULL)
    {
      char *tmp;
      new_deriv->from = (char *) (new_deriv + 1);
      tmp = memcpy (new_deriv + 1, fromset, fromset_len);
      tmp += fromset_len;

      new_deriv->to = memcpy (tmp,
			      toset, toset_len);

      new_deriv->steps = handle;
      new_deriv->nsteps = nsteps;

      if (tsearch (new_deriv, &known_derivations, derivation_compare)
	  == NULL)
	/* There is some kind of memory allocation problem.  */
	free (new_deriv);
    }
  /* Please note that we don't complain if the allocation failed.  This
     is not tragically but in case we use the memory debugging facilities
     not all memory will be freed.  */
}

static void
free_derivation (void *p)
{
  struct known_derivation *deriv = (struct known_derivation *) p;
  size_t cnt;

  for (cnt = 0; cnt < deriv->nsteps; ++cnt)
    if (deriv->steps[cnt].__counter > 0
	&& deriv->steps[cnt].__end_fct != NULL)
      deriv->steps[cnt].__end_fct (&deriv->steps[cnt]);

  /* Free the name strings.  */
  free ((char *) deriv->steps[0].__from_name);
  free ((char *) deriv->steps[deriv->nsteps - 1].__to_name);

  free ((struct __gconv_step *) deriv->steps);
  free (deriv);
}


/* Decrement the reference count for a single step in a steps array.  */
void
internal_function
__gconv_release_step (struct __gconv_step *step)
{
  if (--step->__counter == 0)
    {
      /* Call the destructor.  */
      if (step->__end_fct != NULL)
	step->__end_fct (step);

#ifndef STATIC_GCONV
      /* Skip builtin modules; they are not reference counted.  */
      if (step->__shlib_handle != NULL)
	{
	  /* Release the loaded module.  */
	  __gconv_release_shlib (step->__shlib_handle);
	  step->__shlib_handle = NULL;
	}
#endif
    }
}

static int
internal_function
gen_steps (struct derivation_step *best, const char *toset,
	   const char *fromset, struct __gconv_step **handle, size_t *nsteps)
{
  size_t step_cnt = 0;
  struct __gconv_step *result;
  struct derivation_step *current;
  int status = __GCONV_NOMEM;

  /* First determine number of steps.  */
  for (current = best; current->last != NULL; current = current->last)
    ++step_cnt;

  result = (struct __gconv_step *) malloc (sizeof (struct __gconv_step)
					   * step_cnt);
  if (result != NULL)
    {
      int failed = 0;

      status = __GCONV_OK;
      *nsteps = step_cnt;
      current = best;
      while (step_cnt-- > 0)
	{
	  result[step_cnt].__from_name = (step_cnt == 0
					  ? strdup (fromset)
					  : (char *)current->last->result_set);
	  result[step_cnt].__to_name = (step_cnt + 1 == *nsteps
					? strdup (current->result_set)
					: result[step_cnt + 1].__from_name);

	  result[step_cnt].__counter = 1;
	  result[step_cnt].__data = NULL;

#ifndef STATIC_GCONV
	  if (current->code->module_name[0] == '/')
	    {
	      /* Load the module, return handle for it.  */
	      struct __gconv_loaded_object *shlib_handle =
		__gconv_find_shlib (current->code->module_name);

	      if (shlib_handle == NULL)
		{
		  failed = 1;
		  break;
		}

	      result[step_cnt].__shlib_handle = shlib_handle;
	      result[step_cnt].__modname = shlib_handle->name;
	      result[step_cnt].__fct = shlib_handle->fct;
	      result[step_cnt].__init_fct = shlib_handle->init_fct;
	      result[step_cnt].__end_fct = shlib_handle->end_fct;

	      /* Call the init function.  */
	      if (result[step_cnt].__init_fct != NULL)
		{
		  status = result[step_cnt].__init_fct (&result[step_cnt]);

		  if (__builtin_expect (status, __GCONV_OK) != __GCONV_OK)
		    {
		      failed = 1;
		      /* Make sure we unload this modules.  */
		      --step_cnt;
		      result[step_cnt].__end_fct = NULL;
		      break;
		    }
		}
	    }
	  else
#endif
	    /* It's a builtin transformation.  */
	    __gconv_get_builtin_trans (current->code->module_name,
				       &result[step_cnt]);

	  current = current->last;
	}

      if (__builtin_expect (failed, 0) != 0)
	{
	  /* Something went wrong while initializing the modules.  */
	  while (++step_cnt < *nsteps)
	    __gconv_release_step (&result[step_cnt]);
	  free (result);
	  *nsteps = 0;
	  *handle = NULL;
	  if (status == __GCONV_OK)
	    status = __GCONV_NOCONV;
	}
      else
	*handle = result;
    }
  else
    {
      *nsteps = 0;
      *handle = NULL;
    }

  return status;
}


#ifndef STATIC_GCONV
static int
internal_function
increment_counter (struct __gconv_step *steps, size_t nsteps)
{
  /* Increment the user counter.  */
  size_t cnt = nsteps;
  int result = __GCONV_OK;

  while (cnt-- > 0)
    {
      struct __gconv_step *step = &steps[cnt];

      if (step->__counter++ == 0)
	{
	  /* Skip builtin modules.  */
	  if (step->__modname != NULL)
	    {
	      /* Reopen a previously used module.  */
	      step->__shlib_handle = __gconv_find_shlib (step->__modname);
	      if (step->__shlib_handle == NULL)
		{
		  /* Oops, this is the second time we use this module
		     (after unloading) and this time loading failed!?  */
		  --step->__counter;
		  while (++cnt < nsteps)
		    __gconv_release_step (&steps[cnt]);
		  result = __GCONV_NOCONV;
		  break;
		}

	      /* The function addresses defined by the module may
		 have changed.  */
	      step->__fct = step->__shlib_handle->fct;
	      step->__init_fct = step->__shlib_handle->init_fct;
	      step->__end_fct = step->__shlib_handle->end_fct;
	    }

	  if (step->__init_fct != NULL)
	    step->__init_fct (step);
	}
    }
  return result;
}
#endif


/* The main function: find a possible derivation from the `fromset' (either
   the given name or the alias) to the `toset' (again with alias).  */
static int
internal_function
find_derivation (const char *toset, const char *toset_expand,
		 const char *fromset, const char *fromset_expand,
		 struct __gconv_step **handle, size_t *nsteps)
{
  struct derivation_step *first, *current, **lastp, *solution = NULL;
  int best_cost_hi = INT_MAX;
  int best_cost_lo = INT_MAX;
  int result;

  /* Look whether an earlier call to `find_derivation' has already
     computed a possible derivation.  If so, return it immediately.  */
  result = derivation_lookup (fromset_expand ?: fromset, toset_expand ?: toset,
			      handle, nsteps);
  if (result == __GCONV_OK)
    {
#ifndef STATIC_GCONV
      result = increment_counter (*handle, *nsteps);
#endif
      return result;
    }

  /* The task is to find a sequence of transformations, backed by the
     existing modules - whether builtin or dynamically loadable -,
     starting at `fromset' (or `fromset_expand') and ending at `toset'
     (or `toset_expand'), and with minimal cost.

     For computer scientists, this is a shortest path search in the
     graph where the nodes are all possible charsets and the edges are
     the transformations listed in __gconv_modules_db.

     For now we use a simple algorithm with quadratic runtime behaviour.
     A breadth-first search, starting at `fromset' and `fromset_expand'.
     The list starting at `first' contains all nodes that have been
     visited up to now, in the order in which they have been visited --
     excluding the goal nodes `toset' and `toset_expand' which get
     managed in the list starting at `solution'.
     `current' walks through the list starting at `first' and looks
     which nodes are reachable from the current node, adding them to
     the end of the list [`first' or `solution' respectively] (if
     they are visited the first time) or updating them in place (if
     they have have already been visited).
     In each node of either list, cost_lo and cost_hi contain the
     minimum cost over any paths found up to now, starting at `fromset'