binhash.c

[詳解]

/*++
/* NAME
/*  binhash 3
/* SUMMARY
/*  hash table manager
/* SYNOPSIS
/*  #include <binhash.h>
/*
/*  typedef struct {
/* .in +4
/*      void    *key;
/*      ssize_t key_len;
/*      void    *value;
/*      /* private fields... */
/* .in -4
/*  } BINHASH_INFO;
/*
/*  BINHASH *binhash_create(size)
/*  ssize_t size;
/*
/*  BINHASH_INFO *binhash_enter(table, key, key_len, value)
/*  BINHASH *table;
/*  const void *key;
/*  ssize_t key_len;
/*  void    *value;
/*
/*  char    *binhash_find(table, key, key_len)
/*  BINHASH *table;
/*  const void *key;
/*  ssize_t key_len;
/*
/*  BINHASH_INFO *binhash_locate(table, key, key_len)
/*  BINHASH *table;
/*  const void *key;
/*  ssize_t key_len;
/*
/*  void    binhash_delete(table, key, key_len, free_fn)
/*  BINHASH *table;
/*  const void *key;
/*  ssize_t key_len;
/*  void    (*free_fn)(void *);
/*
/*  void    binhash_free(table, free_fn)
/*  BINHASH *table;
/*  void    (*free_fn)(void *);
/*
/*  void    binhash_walk(table, action, ptr)
/*  BINHASH *table;
/*  void    (*action)(BINHASH_INFO *info, void *ptr);
/*  void    *ptr;
/*
/*  BINHASH_INFO **binhash_list(table)
/*  BINHASH *table;
/* DESCRIPTION
/*  This module maintains one or more hash tables. Each table entry
/*  consists of a unique binary-valued lookup key and a generic
/*  character-pointer value.
/*  The tables are automatically resized when they fill up. When the
/*  values to be remembered are not character pointers, proper casts
/*  should be used or the code will not be portable.
/*
/*  binhash_create() creates a table of the specified size and returns a
/*  pointer to the result. The lookup keys are saved with mymemdup().
/*
/*  binhash_enter() stores a (key, value) pair into the specified table
/*  and returns a pointer to the resulting entry. The code does not
/*  check if an entry with that key already exists: use binhash_locate()
/*  for updating an existing entry. The key is copied; the value is not.
/*
/*  binhash_find() returns the value that was stored under the given key,
/*  or a null pointer if it was not found. In order to distinguish
/*  a null value from a non-existent value, use binhash_locate().
/*
/*  binhash_locate() returns a pointer to the entry that was stored
/*  for the given key, or a null pointer if it was not found.
/*
/*  binhash_delete() removes one entry that was stored under the given key.
/*  If the free_fn argument is not a null pointer, the corresponding
/*  function is called with as argument the value that was stored under
/*  the key.
/*
/*  binhash_free() destroys a hash table, including contents. If the free_fn
/*  argument is not a null pointer, the corresponding function is called
/*  for each table entry, with as argument the value that was stored
/*  with the entry.
/*
/*  binhash_walk() invokes the action function for each table entry, with
/*  a pointer to the entry as its argument. The ptr argument is passed
/*  on to the action function.
/*
/*  binhash_list() returns a null-terminated list of pointers to
/*  all elements in the named table. The list should be passed to
/*  myfree().
/* RESTRICTIONS
/*  A callback function should not modify the hash table that is
/*  specified to its caller.
/* DIAGNOSTICS
/*  The following conditions are reported and cause the program to
/*  terminate immediately: memory allocation failure; an attempt
/*  to delete a non-existent entry.
/* SEE ALSO
/*  mymalloc(3) memory management wrapper
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/

/* C library */

#include <sys_defs.h>
#include <string.h>

/* Local stuff */

#include "mymalloc.h"
#include "msg.h"
#include "binhash.h"

/* binhash_hash - hash a string */

static size_t binhash_hash(const void *key, ssize_t len, size_t size)
{
    size_t  h = 0;
    size_t  g;

    /*
     * From the "Dragon" book by Aho, Sethi and Ullman.
     */

    while (len-- > 0) {
    h = (h << 4U) + *(unsigned const char *) key++;
    if ((g = (h & 0xf0000000)) != 0) {
        h ^= (g >> 24U);
        h ^= g;
    }
    }
    return (h % size);
}

/* binhash_link - insert element into table */

#define binhash_link(table, elm) { \
    BINHASH_INFO **_h = table->data + binhash_hash(elm->key, elm->key_len, table->size);\
    elm->prev = 0; \
    if ((elm->next = *_h) != 0) \
    (*_h)->prev = elm; \
    *_h = elm; \
    table->used++; \
}

/* binhash_size - allocate and initialize hash table */

static void binhash_size(BINHASH *table, size_t size)
{
    BINHASH_INFO **h;

    size |= 1;

    table->data = h = (BINHASH_INFO **) mymalloc(size * sizeof(BINHASH_INFO *));
    table->size = size;
    table->used = 0;

    while (size-- > 0)
    *h++ = 0;
}

/* binhash_create - create initial hash table */

BINHASH *binhash_create(ssize_t size)
{
    BINHASH *table;

    table = (BINHASH *) mymalloc(sizeof(BINHASH));
    binhash_size(table, size < 13 ? 13 : size);
    return (table);
}

/* binhash_grow - extend existing table */

static void binhash_grow(BINHASH *table)
{
    BINHASH_INFO *ht;
    BINHASH_INFO *next;
    ssize_t old_size = table->size;
    BINHASH_INFO **h = table->data;
    BINHASH_INFO **old_entries = h;

    binhash_size(table, 2 * old_size);

    while (old_size-- > 0) {
    for (ht = *h++; ht; ht = next) {
        next = ht->next;
        binhash_link(table, ht);
    }
    }
    myfree((void *) old_entries);
}

/* binhash_enter - enter (key, value) pair */

BINHASH_INFO *binhash_enter(BINHASH *table, const void *key, ssize_t key_len, void *value)
{
    BINHASH_INFO *ht;

    if (table->used >= table->size)
    binhash_grow(table);
    ht = (BINHASH_INFO *) mymalloc(sizeof(BINHASH_INFO));
    ht->key = mymemdup(key, key_len);
    ht->key_len = key_len;
    ht->value = value;
    binhash_link(table, ht);
    return (ht);
}

/* binhash_find - lookup value */

void   *binhash_find(BINHASH *table, const void *key, ssize_t key_len)
{
    BINHASH_INFO *ht;

#define KEY_EQ(x,y,l) (((unsigned char *) x)[0] == ((unsigned char *) y)[0] && memcmp(x,y,l) == 0)

    if (table != 0)
    for (ht = table->data[binhash_hash(key, key_len, table->size)]; ht; ht = ht->next)
        if (key_len == ht->key_len && KEY_EQ(key, ht->key, key_len))
        return (ht->value);
    return (0);
}

/* binhash_locate - lookup entry */

BINHASH_INFO *binhash_locate(BINHASH *table, const void *key, ssize_t key_len)
{
    BINHASH_INFO *ht;

    if (table != 0)
    for (ht = table->data[binhash_hash(key, key_len, table->size)]; ht; ht = ht->next)
        if (key_len == ht->key_len && KEY_EQ(key, ht->key, key_len))
        return (ht);
    return (0);
}

/* binhash_delete - delete one entry */

void    binhash_delete(BINHASH *table, const void *key, ssize_t key_len, void (*free_fn) (void *))
{
    if (table != 0) {
    BINHASH_INFO *ht;
    BINHASH_INFO **h = table->data + binhash_hash(key, key_len, table->size);

    for (ht = *h; ht; ht = ht->next) {
        if (key_len == ht->key_len && KEY_EQ(key, ht->key, key_len)) {
        if (ht->next)
            ht->next->prev = ht->prev;
        if (ht->prev)
            ht->prev->next = ht->next;
        else
            *h = ht->next;
        table->used--;
        myfree(ht->key);
        if (free_fn)
            (*free_fn) (ht->value);
        myfree((void *) ht);
        return;
        }
    }
    msg_panic("binhash_delete: unknown_key: \"%s\"", (char *) key);
    }
}

/* binhash_free - destroy hash table */

void    binhash_free(BINHASH *table, void (*free_fn) (void *))
{
    if (table != 0) {
    ssize_t i = table->size;
    BINHASH_INFO *ht;
    BINHASH_INFO *next;
    BINHASH_INFO **h = table->data;

    while (i-- > 0) {
        for (ht = *h++; ht; ht = next) {
        next = ht->next;
        myfree(ht->key);
        if (free_fn)
            (*free_fn) (ht->value);
        myfree((void *) ht);
        }
    }
    myfree((void *) table->data);
    table->data = 0;
    myfree((void *) table);
    }
}

/* binhash_walk - iterate over hash table */

void    binhash_walk(BINHASH *table, void (*action) (BINHASH_INFO *, void *),
                     void *ptr) {
    if (table != 0) {
    ssize_t i = table->size;
    BINHASH_INFO **h = table->data;
    BINHASH_INFO *ht;

    while (i-- > 0)
        for (ht = *h++; ht; ht = ht->next)
        (*action) (ht, ptr);
    }
}

/* binhash_list - list all table members */

BINHASH_INFO **binhash_list(table)
BINHASH *table;
{
    BINHASH_INFO **list;
    BINHASH_INFO *member;
    ssize_t count = 0;
    ssize_t i;

    if (table != 0) {
    list = (BINHASH_INFO **) mymalloc(sizeof(*list) * (table->used + 1));
    for (i = 0; i < table->size; i++)
        for (member = table->data[i]; member != 0; member = member->next)
        list[count++] = member;
    } else {
    list = (BINHASH_INFO **) mymalloc(sizeof(*list));
    }
    list[count] = 0;
    return (list);
}