json-c/linkhash.h

/*
 * $Id: linkhash.h,v 1.6 2006/01/30 23:07:57 mclark Exp $
 *
 * Copyright (c) 2004, 2005 Metaparadigm Pte. Ltd.
 * Michael Clark <michael@metaparadigm.com>
 * Copyright (c) 2009 Hewlett-Packard Development Company, L.P.
 *
 * This library is free software; you can redistribute it and/or modify
 * it under the terms of the MIT license. See COPYING for details.
 *
 */

/**
 * @file
 * @brief Internal methods for working with json_type_object objects.  Although
 *        this is exposed by the json_object_get_object() function and within the
 *        json_object_iter type, it is not recommended for direct use.
 */
#ifndef _json_c_linkhash_h_
#define _json_c_linkhash_h_

#include "json_object.h"
#include <stdio.h>

#ifdef __cplusplus
extern "C" {
#endif

/**
 * golden prime used in hash functions
 */
#define LH_PRIME 0x9e370001UL

/**
 * The fraction of filled hash buckets until an insert will cause the table
 * to be resized.
 * This can range from just above 0 up to 1.0.
 */
#define LH_LOAD_FACTOR 0.66

/**
 * sentinel pointer value for empty slots
 */
#define LH_EMPTY (void *)-1

/**
 * sentinel pointer value for freed slots
 */
#define LH_FREED (void *)-2

/**
 * default string hash function
 */
#define JSON_C_STR_HASH_DFLT 0

/**
 * perl-like string hash function
 */
#define JSON_C_STR_HASH_PERLLIKE 1

/**
 * This function sets the hash function to be used for strings.
 * Must be one of the JSON_C_STR_HASH_* values.
 * @returns 0 - ok, -1 if parameter was invalid
 */
int json_global_set_string_hash(const int h);

struct lh_entry;

/**
 * callback function prototypes
 */
typedef void(lh_entry_free_fn)(struct lh_entry *e);
/**
 * callback function prototypes
 */
typedef unsigned long(lh_hash_fn)(const void *k);
/**
 * callback function prototypes
 */
typedef int(lh_equal_fn)(const void *k1, const void *k2);

/**
 * @brief A buffer of characters that may contain null charaters in the middle
 *
 * A buffer of data that can hold a normal null-terminated string
 * (in which case `length` should just be equal to `strlen`)
 * or a string with embedded null characters (in which case `length` reflects
 * all the characters that make up the "string").
 * Either way, this struct can be treated as if it contains null characters,
 * since the `length` member should always be equal to the proper size of the
 * buffer and the terminating null character wouldn't be included
 * (it wouldn't be counted by strlen).
 */
struct lh_string
{
	/**
	 * @brief Stores the length of the buffer
	 *
	 * If the length is positive, then `pdata` should be used.
	 * Otherwise, idata should be used.
	 */
	ssize_t length;
	union
	{
		const char *pdata;
		const char idata[0];
	} str;
};

/**
 * An entry in the hash table
 */
struct lh_entry
{
	/**
	 * The key.  Use lh_entry_k() instead of accessing this directly.
	 */
	const void *k;
	/**
	 * A flag for users of linkhash to know whether or not they
	 * need to free k.
	 */
	int k_is_constant;
	/**
	 * The value.  Use lh_entry_v() instead of accessing this directly.
	 */
	const void *v;
	/**
	 * The next entry
	 */
	struct lh_entry *next;
	/**
	 * The previous entry.
	 */
	struct lh_entry *prev;
};

/**
 * The hash table structure.
 */
struct lh_table
{
	/**
	 * Size of our hash.
	 */
	int size;
	/**
	 * Numbers of entries.
	 */
	int count;

	/**
	 * The first entry.
	 */
	struct lh_entry *head;

	/**
	 * The last entry.
	 */
	struct lh_entry *tail;

	struct lh_entry *table;

	/**
	 * A pointer onto the function responsible for freeing an entry.
	 */
	lh_entry_free_fn *free_fn;
	/**
	 * A function that is capable of hashing entries in this table
	 */
	lh_hash_fn *hash_fn;
	/**
	 * A function that is capable of determining if entries in this table
	 * are equal
	 */
	lh_equal_fn *equal_fn;
};
typedef struct lh_table lh_table;

/**
 * Convenience list iterator.
 */
#define lh_foreach(table, entry) for (entry = table->head; entry; entry = entry->next)

/**
 * lh_foreach_safe allows calling of deletion routine while iterating.
 *
 * @param table a struct lh_table * to iterate over
 * @param entry a struct lh_entry * variable to hold each element
 * @param tmp a struct lh_entry * variable to hold a temporary pointer to the next element
 */
#define lh_foreach_safe(table, entry, tmp) \
	for (entry = table->head; entry && ((tmp = entry->next) || 1); entry = tmp)

/**
 * @brief Get the data from a `struct lh_string *`
 *
 * @param str value to retrieve the data from
 */
extern const char *lh_string_data(const struct lh_string *str);

/**
 * @brief Get the length of the data stored in a `struct lh_string *`
 *
 * @param str value to retrieve the length of
 */
extern size_t lh_string_size(const struct lh_string *str);

/**
 * @brief Print a `struct lh_string` to a given stream
 *
 * @param str value to print
 * @param stream Stream to write data to
 */
extern size_t lh_string_print(const struct lh_string *str, FILE *stream);

/**
 * @brief Creates a new `struct lh_string` using the `pdata` field.
 *
 * This avoids unneeded copying, for cases wher ethe key is in an area of
 * memory that will not be modified or freed until after this object is freed.
 *
 * @param length The length of the data located at @p data
 * @param data The data to include
 * @return `NULL` on error
 */
extern struct lh_string *lh_string_new_ptr(const size_t length, const char *data);

/**
 * @brief Creates a new `struct lh_string` using the `idata` field.
 *
 * @param length The length of the data to copy into the returned value
 * @param data The data to include and copy into the returned value
 * @return `NULL` on error
 */
extern struct lh_string *lh_string_new_imm(const size_t length, const char *data);

/**
 * Create a new linkhash table.
 *
 * @param size initial table size. The table is automatically resized
 * although this incurs a performance penalty.
 * @param free_fn callback function used to free memory for entries
 * when lh_table_free or lh_table_delete is called.
 * If NULL is provided, then memory for keys and values
 * must be freed by the caller.
 * @param hash_fn  function used to hash keys. 2 standard ones are defined:
 * lh_ptr_hash and lh_char_hash for hashing pointer values
 * and C strings respectively.
 * @param equal_fn comparison function to compare keys. 2 standard ones defined:
 * lh_ptr_hash and lh_char_hash for comparing pointer values
 * and C strings respectively.
 * @return On success, a pointer to the new linkhash table is returned.
 * 	On error, a null pointer is returned.
 */
extern struct lh_table *lh_table_new(int size, lh_entry_free_fn *free_fn, lh_hash_fn *hash_fn,
                                     lh_equal_fn *equal_fn);

/**
 * Convenience function to create a new linkhash table with char keys.
 *
 * @param size initial table size.
 * @param free_fn callback function used to free memory for entries.
 * @return On success, a pointer to the new linkhash table is returned.
 * 	On error, a null pointer is returned.
 */
extern struct lh_table *lh_kchar_table_new(int size, lh_entry_free_fn *free_fn);

/**
 * Convenience function to create a new linkhash table with ptr keys.
 *
 * @param size initial table size.
 * @param free_fn callback function used to free memory for entries.
 * @return On success, a pointer to the new linkhash table is returned.
 * 	On error, a null pointer is returned.
 */
extern struct lh_table *lh_kptr_table_new(int size, lh_entry_free_fn *free_fn);

/**
 * Free a linkhash table.
 *
 * If a lh_entry_free_fn callback free function was provided then it is
 * called for all entries in the table.
 *
 * @param t table to free.
 */
extern void lh_table_free(struct lh_table *t);

/**
 * Insert a record into the table.
 *
 * @param t the table to insert into.
 * @param k a pointer to the key to insert.
 * @param v a pointer to the value to insert.
 *
 * @return On success, <code>0</code> is returned.
 * 	On error, a negative value is returned.
 */
extern int lh_table_insert(struct lh_table *t, const void *k, const void *v);

/**
 * Insert a record into the table using a precalculated key hash.
 *
 * The hash h, which should be calculated with lh_get_hash() on k, is provided by
 *  the caller, to allow for optimization when multiple operations with the same
 *  key are known to be needed.
 *
 * @param t the table to insert into.
 * @param k a pointer to the key to insert.
 * @param v a pointer to the value to insert.
 * @param h hash value of the key to insert
 * @param opts if set to JSON_C_OBJECT_KEY_IS_CONSTANT, sets lh_entry.k_is_constant
 *             so t's free function knows to avoid freeing the key.
 */
extern int lh_table_insert_w_hash(struct lh_table *t, const void *k, const void *v,
                                  const unsigned long h, const unsigned opts);

/**
 * Lookup a record in the table.
 *
 * @param t the table to lookup
 * @param k a pointer to the key to lookup
 * @return a pointer to the record structure of the value or NULL if it does not exist.
 */
extern struct lh_entry *lh_table_lookup_entry(struct lh_table *t, const void *k);

/**
 * Lookup a record in the table using a precalculated key hash.
 *
 * The hash h, which should be calculated with lh_get_hash() on k, is provided by
 *  the caller, to allow for optimization when multiple operations with the same
 *  key are known to be needed.
 *
 * @param t the table to lookup
 * @param k a pointer to the key to lookup
 * @param h hash value of the key to lookup
 * @return a pointer to the record structure of the value or NULL if it does not exist.
 */
extern struct lh_entry *lh_table_lookup_entry_w_hash(struct lh_table *t, const void *k,
                                                     const unsigned long h);

/**
 * Lookup a record in the table.
 *
 * @param t the table to lookup
 * @param k a pointer to the key to lookup
 * @param v a pointer to a where to store the found value (set to NULL if it doesn't exist).
 * @return whether or not the key was found
 */
extern json_bool lh_table_lookup_ex(struct lh_table *t, const void *k, void **v);

/**
 * Delete a record from the table.
 *
 * If a callback free function is provided then it is called for the
 * for the item being deleted.
 * @param t the table to delete from.
 * @param e a pointer to the entry to delete.
 * @return 0 if the item was deleted.
 * @return -1 if it was not found.
 */
extern int lh_table_delete_entry(struct lh_table *t, struct lh_entry *e);

/**
 * Delete a record from the table.
 *
 * If a callback free function is provided then it is called for the
 * for the item being deleted.
 * @param t the table to delete from.
 * @param k a pointer to the key to delete.
 * @return 0 if the item was deleted.
 * @return -1 if it was not found.
 */
extern int lh_table_delete(struct lh_table *t, const void *k);

extern int lh_table_length(struct lh_table *t);

/**
 * Resizes the specified table.
 *
 * @param t Pointer to table to resize.
 * @param new_size New table size. Must be positive.
 *
 * @return On success, <code>0</code> is returned.
 * 	On error, a negative value is returned.
 */
int lh_table_resize(struct lh_table *t, int new_size);

/**
 * @deprecated Don't use this outside of linkhash.h:
 */
#if (defined(AIX_CC) || (defined(_MSC_VER) && (_MSC_VER <= 1800)))
/* VS2010 can't handle inline funcs, so skip it there */
#define _LH_INLINE
#else
#define _LH_INLINE inline
#endif

/**
 * Calculate the hash of a key for a given table.
 *
 * This is an exension to support functions that need to calculate
 * the hash several times and allows them to do it just once and then pass
 * in the hash to all utility functions. Depending on use case, this can be a
 * considerable performance improvement.
 * @param t the table (used to obtain hash function)
 * @param k a pointer to the key to lookup
 * @return the key's hash
 */
static _LH_INLINE unsigned long lh_get_hash(const struct lh_table *t, const void *k)
{
	return t->hash_fn(k);
}

#undef _LH_INLINE

/**
 * @deprecated Don't use this outside of linkhash.h:
 */
#ifdef __UNCONST
#define _LH_UNCONST(a) __UNCONST(a)
#else
#define _LH_UNCONST(a) ((void *)(uintptr_t)(const void *)(a))
#endif

/**
 * Return a non-const version of lh_entry.k.
 *
 * lh_entry.k is const to indicate and help ensure that linkhash itself doesn't modify
 * it, but callers are allowed to do what they want with it.
 * See also lh_entry.k_is_constant
 */
#define lh_entry_k(entry) _LH_UNCONST((entry)->k)

/**
 * Return a non-const version of lh_entry.v.
 *
 * v is const to indicate and help ensure that linkhash itself doesn't modify
 * it, but callers are allowed to do what they want with it.
 */
#define lh_entry_v(entry) _LH_UNCONST((entry)->v)

#ifdef __cplusplus
}
#endif

#endif