include/atalk/hash.h

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/*
 * Hash Table Data Type
 * Copyright (C) 1997 Kaz Kylheku <[email protected]>
 *
 * Free Software License:
 *
 * All rights are reserved by the author, with the following exceptions:
 * Permission is granted to freely reproduce and distribute this software,
 * possibly in exchange for a fee, provided that this copyright notice appears
 * intact. Permission is also granted to adapt this software to produce
 * derivative works, as long as the modified versions carry this copyright
 * notice and additional notices stating that the work has been modified.
 * This source code may be translated into executable form and incorporated
 * into proprietary software; there is no requirement for such software to
 * contain a copyright notice related to this source.
 *
 * $Name:  $
 */
 
#ifndef ATALK_HASH_H
#define ATALK_HASH_H
 
#include <limits.h>
#include <stdint.h>
 
typedef unsigned long hashcount_t;
#define HASHCOUNT_T_MAX ULONG_MAX
 
typedef uint32_t hash_val_t;
#define HASH_VAL_T_MAX UINT32_MAX
 
extern int hash_val_t_bit;
 
#ifndef HASH_VAL_T_BIT
#define HASH_VAL_T_BIT ((int) hash_val_t_bit)
#endif
 
/*
 * Hash chain node structure.
 * Notes:
 * 1. This preprocessing directive is for debugging purposes.  The effect is
 *    that if the preprocessor symbol KAZLIB_OPAQUE_DEBUG is defined prior to the
 *    inclusion of this header,  then the structure shall be declared as having
 *    the single member   int __OPAQUE__.   This way, any attempts by the
 *    client code to violate the principles of information hiding (by accessing
 *    the structure directly) can be diagnosed at translation time. However,
 *    note the resulting compiled unit is not suitable for linking.
 * 2. This is a pointer to the next node in the chain. In the last node of a
 *    chain, this pointer is null.
 * 3. The key is a pointer to some user supplied data that contains a unique
 *    identifier for each hash node in a given table. The interpretation of
 *    the data is up to the user. When creating or initializing a hash table,
 *    the user must supply a pointer to a function for comparing two keys,
 *    and a pointer to a function for hashing a key into a numeric value.
 * 4. The value is a user-supplied pointer to void which may refer to
 *    any data object. It is not interpreted in any way by the hashing
 *    module.
 * 5. The hashed key is stored in each node so that we don't have to rehash
 *    each key when the table must grow or shrink.
 */
 
typedef struct hnode_t {
#if defined(HASH_IMPLEMENTATION) || !defined(KAZLIB_OPAQUE_DEBUG)   /* 1 */
    struct hnode_t *hash_next;      /* 2 */
    const void *hash_key;       /* 3 */
    void *hash_data;           /* 4 */
    hash_val_t hash_hkey;        /* 5 */
#else
    int hash_dummy;
#endif
} hnode_t;
 
/*
 * The comparison function pointer type. A comparison function takes two keys
 * and produces a value of -1 if the left key is less than the right key, a
 * value of 0 if the keys are equal, and a value of 1 if the left key is
 * greater than the right key.
 */
 
typedef int (*hash_comp_t)(const void *, const void *);
 
/*
 * The hashing function performs some computation on a key and produces an
 * integral value of type hash_val_t based on that key. For best results, the
 * function should have a good randomness properties in *all* significant bits
 * over the set of keys that are being inserted into a given hash table. In
 * particular, the most significant bits of hash_val_t are most significant to
 * the hash module. Only as the hash table expands are less significant bits
 * examined. Thus a function that has good distribution in its upper bits but
 * not lower is preferrable to one that has poor distribution in the upper bits
 * but not the lower ones.
 */
 
typedef hash_val_t (*hash_fun_t)(const void *);
 
/*
 * allocator functions
 */
 
typedef hnode_t *(*hnode_alloc_t)(void *);
typedef void (*hnode_free_t)(hnode_t *, void *);
 
/*
 * This is the hash table control structure. It keeps track of information
 * about a hash table, as well as the hash table itself.
 * Notes:
 * 1.  Pointer to the hash table proper. The table is an array of pointers to
 *     hash nodes (of type hnode_t). If the table is empty, every element of
 *     this table is a null pointer. A non-null entry points to the first
 *     element of a chain of nodes.
 * 2.  This member keeps track of the size of the hash table---that is, the
 *     number of chain pointers.
 * 3.  The count member maintains the number of elements that are presently
 *     in the hash table.
 * 4.  The maximum count is the greatest number of nodes that can populate this
 *     table. If the table contains this many nodes, no more can be inserted,
 *     and the hash_isfull() function returns true.
 * 5.  The high mark is a population threshold, measured as a number of nodes,
 *     which, if exceeded, will trigger a table expansion. Only dynamic hash
 *     tables are subject to this expansion.
 * 6.  The low mark is a minimum population threshold, measured as a number of
 *     nodes. If the table population drops below this value, a table shrinkage
 *     will occur. Only dynamic tables are subject to this reduction.  No table
 *     will shrink beneath a certain absolute minimum number of nodes.
 * 7.  This is the a pointer to the hash table's comparison function. The
 *     function is set once at initialization or creation time.
 * 8.  Pointer to the table's hashing function, set once at creation or
 *     initialization time.
 * 9.  The current hash table mask. If the size of the hash table is 2^N,
 *     this value has its low N bits set to 1, and the others clear. It is used
 *     to select bits from the result of the hashing function to compute an
 *     index into the table.
 * 10. A flag which indicates whether the table is to be dynamically resized. It
 *     is set to 1 in dynamically allocated tables, 0 in tables that are
 *     statically allocated.
 */
 
typedef struct hash_t {
#if defined(HASH_IMPLEMENTATION) || !defined(KAZLIB_OPAQUE_DEBUG)
    struct hnode_t **hash_table;       /* 1 */
    hashcount_t hash_nchains;            /* 2 */
    hashcount_t hash_nodecount;            /* 3 */
    hashcount_t hash_maxcount;          /* 4 */
    hashcount_t hash_highmark;          /* 5 */
    hashcount_t hash_lowmark;            /* 6 */
    hash_comp_t hash_compare;            /* 7 */
    hash_fun_t hash_function;            /* 8 */
    hnode_alloc_t hash_allocnode;
    hnode_free_t hash_freenode;
    void *hash_context;
    hash_val_t hash_mask;            /* 9 */
    int hash_dynamic;               /* 10 */
#else
    int hash_dummy;
#endif
} hash_t;
 
/*
 * Hash scanner structure, used for traversals of the data structure.
 * Notes:
 * 1. Pointer to the hash table that is being traversed.
 * 2. Reference to the current chain in the table being traversed (the chain
 *    that contains the next node that shall be retrieved).
 * 3. Pointer to the node that will be retrieved by the subsequent call to
 *    hash_scan_next().
 */
 
typedef struct hscan_t {
#if defined(HASH_IMPLEMENTATION) || !defined(KAZLIB_OPAQUE_DEBUG)
    hash_t *hash_table;     /* 1 */
    hash_val_t hash_chain;  /* 2 */
    hnode_t *hash_next;     /* 3 */
#else
    int hash_dummy;
#endif
} hscan_t;
 
 
#endif /* ATALK_HASH_H */