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/* objc-map.h -- Implementation of map data structures for ObjC compiler

   Copyright 2011 Free Software Foundation, Inc.

   Written by Nicola Pero <nicola.pero@meta-innovation.com>

This program is free software; you can redistribute it and/or modify it

under the terms of the GNU Lesser Public License as published by the

Free Software Foundation; either version 3, 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 Lesser Public License for more details.

You should have received a copy of the GNU Lesser Public License

along with this program; if not, write to the Free Software

Foundation, 51 Franklin Street - Fifth Floor,

Boston, MA 02110-1301, USA.  */

#ifndef OBJC_MAP_H

#define OBJC_MAP_H

/* A map is a data structure that maps a key to a value.  In this file

   we currently have maps that can map a GCC identifier (a tree) to

   some other GCC tree.  This is what the ObjC frontend mostly needs:

   being able to look up an identifier into an ObjC data structure.  A

   typical usage is mapping ObjC class names (as identifiers) to a

   tree representing the class.

   This implementation is fast.  :-) */

/**

 ** Private definitions.

 **/

/* We include private declaration and definitions that are required to

   provide the implementation of inline functions.  You should ignore

   these definitions (and the implementation of the inline functions)

   as they are not part of the public API and may change.  */

typedef unsigned int objc_map_private_hash_t;

/* This is used as sentinel.  */

#define OBJC_MAP_PRIVATE_EMPTY_SLOT (tree)0

struct GTY(()) objc_map_private {

  /* Total number of slots.  This is the maximum number of elements

     that can be currently stored in the map before resizing.  This is

     the number of slots in the C array.  Important: this is

     guaranteed to be a power of 2.  When we create (or resize) the

     map, we round up the size to the next power of 2.  This allows us

     to convert a hash to a position in the hashtable by simply doing

     "position = hash & mask", where mask is number_of_slots - 1

     instead of using a modulo (which requires a division).  */

  size_t number_of_slots;

  /* This is number_of_slots - 1, precomputed.  */

  size_t mask;

  /* Number of slots that are not empty (ie, that are active).  We

     keep counts using this variable which can easily be checked

     against max_number_of_non_empty_slots.  */

  size_t number_of_non_empty_slots;

  /* This is the load factor limit.  When the number of non empty

     slots equals this number, we need to resize the array.  This is

     calculated once, when the slots are resized, and then kept cached

     so it can be compared quickly when elements are added.  */

  size_t max_number_of_non_empty_slots;

  /* The maximum load factor.  */

  int maximum_load_factor;

  /* These are the keys.  */

  tree * GTY ((length ("%h.number_of_slots"))) slots;

  /* These are the values.  values[i] is the the value corresponding

     to slots[i].  */

  tree * GTY ((length ("%h.number_of_slots"))) values;

};

/* Private functions used to resize the map.  They may be called by

   the inline functions when adding elements.  */

extern void

objc_map_private_grow (struct objc_map_private *map);

/**

 ** The definition of a map.

 **/

typedef struct objc_map_private *objc_map_t;

/**

 ** Creating a map.

 **/

/* objc_map_alloc_ggc() creates a new map which is under GGC.  The initial

   capacity must be specified as an argument; this is used to size the map

   when it is created.  */

objc_map_t objc_map_alloc_ggc (size_t initial_capacity);

/**

 ** Performance tuning.

 **/

/* Set a maximum load factor for the data structure.  This is the main

   tuning parameter to improve performance (at the expense of

   memory).  */

void objc_map_set_maximum_load_factor (objc_map_t map, int number_between_zero_and_one_hundred);

/* Read the maximum load factor.  */

int objc_map_maximum_load_factor (objc_map_t map);

/**

 ** Getting the value corresponding to a key.

 **/

/* This is the value returned by objc_map_get() when the value

   corresponding to a key is not found.  */

#define OBJC_MAP_NOT_FOUND (tree)1

/* objc_map_get() returns the value associated with a certain key,

   or OBJC_MAP_NOT_FOUND if there is no value associated with that key.

   Note that you can also use it to simply check if the map contains a

   pair with a certain key; just compare the result of calling

   objc_map_get() to OBJC_MAP_NOT_FOUND.

   It is essential to always check the results of the call to make

   sure it is not OBJC_MAP_NOT_FOUND.

   NULL is a valid value, so a key can be inserted into a map with

   value NULL, and objc_map_get() will return NULL in that case.

   So a result of NULL means that they key *was* found, and the value

   associated with it was NULL.  */

static inline tree

objc_map_get (objc_map_t map, /* struct tree_identifier * */tree key)

{

  /* The inline implementation is private and may change without notice.  */

  objc_map_private_hash_t hash = IDENTIFIER_HASH_VALUE (key);

  size_t i = hash & map->mask;

  size_t j = 1;

  if (map->slots[i] == OBJC_MAP_PRIVATE_EMPTY_SLOT)

    return OBJC_MAP_NOT_FOUND;

  if (map->slots[i] == key)

    return map->values[i];

  while (1)

    {

      i = (i + j) & map->mask;

      if (map->slots[i] == OBJC_MAP_PRIVATE_EMPTY_SLOT)

        return OBJC_MAP_NOT_FOUND;

      if (map->slots[i] == key)

        return map->values[i];

      j++;

    }

}

/* objc_map_put() puts a key/value pair into the map.  If the map does

   not contain the key, it is added to it with the specified value.

   If the map already contains the key, the previous value is replaced

   with the new one.

   You can use any identifier as key, with the exception of NULL.

   You can use any tree as value, including NULL.  */

static inline

void objc_map_put (objc_map_t map, /*struct tree_identifier * */tree key, tree value)

{

  /* The inline implementation is private and may change without notice.  */

  objc_map_private_hash_t hash = IDENTIFIER_HASH_VALUE (key);

  size_t i, j = 0;

  if (map->number_of_non_empty_slots == map->max_number_of_non_empty_slots)

    objc_map_private_grow (map);

  i = hash & map->mask;

  while (1)

    {

      if (map->slots[i] == OBJC_MAP_PRIVATE_EMPTY_SLOT)

        {

          map->number_of_non_empty_slots++;

          map->slots[i] = key;

          map->values[i] = value;

          return;

        }

      if (map->slots[i] == key)

        {

          map->values[i] = value;

          return;

        }

      j++;

      i = (i + j) & map->mask;

    }

}

/**

 ** Iterating over a map using an iterator.

 **/

/* When using iterators you can iterate directly on the elements in

   the map, and take an action over each one.

   Here is how you iterate over a hmap_pointer using iterators:

   objc_map_iterator_t i;

   objc_map_iterator_initialize (map, &i);

   while (objc_map_iterator_move_to_next (map, &i))

     {

       tree p = objc_map_iterator_current_key (map, i);

       tree q = objc_map_iterator_current_value (map, i);

       ... do something with p and q ...

     }

   You'll notice that the functions that modify the iterator (to

   initialize it, or move it to the next element) take a pointer to it

   as argument (as in "&i"), while the functions that only read its

   state (to read the current key/value, or remove the current

   key/value from the map) take it as a direct argument (as in "i").

   Note that all the objc_map_iterator_*() functions are inline and if

   you follow the pattern above, the compiler should be able to inline

   everything into a very efficient loop, roughly equivalent to

   hand-writing a C loop that iterates directly onto the hmap_pointer

   internal data structures.  */

/* A objc_map_iterator_t variable encapsulates the state of an

   iteration.  The fact that this is actually a size_t (pointing to

   the index of the slot that we return next) is an internal, private

   detail of the implementation and may change without notice.  */

typedef size_t objc_map_iterator_t;

/* Initialize an iterator to iterate over the specified objc_map.  You

   must use this before starting the iteration, to get a working

   iterator.  */

static inline

void

objc_map_iterator_initialize (objc_map_t map ATTRIBUTE_UNUSED, objc_map_iterator_t *i)

{

  /* The inline implementation is private and may change without notice.  */

  /* This is trivial, but the same API would work to initialize more

     complicated iterators.  */

  *i = 0;

}

#define OBJC_MAP_FAILURE 0

#define OBJC_MAP_SUCCESS 1

/* Move the iterator to the next key/value pair, and return

   OBJC_MAP_SUCCESS if there is such a key/value pair, and

   OBJC_MAP_FAILURE if there are no more ones.  The iterator must have

   been initialized using objc_map_iterator_initialize().  Note that

   because this function is modifying the iterator, you need to pass a

   pointer to it.  */

static inline

int

objc_map_iterator_move_to_next (objc_map_t map, objc_map_iterator_t *i)

{

  /* The inline implementation is private and may change without notice.  */

  while (1)

    {

      void *slot;

      if (*i == map->number_of_slots)

        return OBJC_MAP_FAILURE;

      slot = map->slots[*i];

      *i = *i + 1;

      if (slot != OBJC_MAP_PRIVATE_EMPTY_SLOT)

        return OBJC_MAP_SUCCESS;

    }

}

/* Return the current key.  You can only call it after you have called

   objc_map_iterator_move_to_next() at least once (to move to the

   first element), and only if the last call returned

   OBJC_MAP_SUCCESS.  The behaviour is otherwise undefined, probably a

   segmentation fault.  */

static inline

tree

objc_map_iterator_current_key (objc_map_t map, objc_map_iterator_t i)

{

  /* The inline implementation is private and may change without notice.  */

  return map->slots[i - 1];

}

/* Return the current value.  You can only call it after you have

   called objc_map_iterator_move_to_next() at least once (to move to

   the first element), and only if the last call returned

   OBJC_MAP_SUCCESS.  The behaviour is otherwise undefined, probably a

   segmentation fault.  */

static inline

tree

objc_map_iterator_current_value (objc_map_t map, objc_map_iterator_t i)

{

  /* The inline implementation is private and may change without notice.  */

  return map->values[i - 1];

}

#endif /* OBJC_MAP_H */