list.c

Go to the documentation of this file.

/*
 *  OpenVPN -- An application to securely tunnel IP networks
 *             over a single TCP/UDP port, with support for SSL/TLS-based
 *             session authentication and key exchange,
 *             packet encryption, packet authentication, and
 *             packet compression.
 *
 *  Copyright (C) 2002-2024 OpenVPN Inc <sales@openvpn.net>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2
 *  as published by the Free Software Foundation.
 *
 *  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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
 
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
 
#include "syshead.h"
 
 
#include "integer.h"
#include "list.h"
#include "misc.h"
 
#include "memdbg.h"
 
struct hash *
hash_init(const int n_buckets,
          const uint32_t iv,
          uint32_t (*hash_function)(const void *key, uint32_t iv),
          bool (*compare_function)(const void *key1, const void *key2))
{
    struct hash *h;
    int i;
 
    ASSERT(n_buckets > 0);
    ALLOC_OBJ_CLEAR(h, struct hash);
    h->n_buckets = (int) adjust_power_of_2(n_buckets);
    h->mask = h->n_buckets - 1;
    h->hash_function = hash_function;
    h->compare_function = compare_function;
    h->iv = iv;
    ALLOC_ARRAY(h->buckets, struct hash_bucket, h->n_buckets);
    for (i = 0; i < h->n_buckets; ++i)
    {
        struct hash_bucket *b = &h->buckets[i];
        b->list = NULL;
    }
    return h;
}
 
void
hash_free(struct hash *hash)
{
    int i;
    for (i = 0; i < hash->n_buckets; ++i)
    {
        struct hash_bucket *b = &hash->buckets[i];
        struct hash_element *he = b->list;
 
        while (he)
        {
            struct hash_element *next = he->next;
            free(he);
            he = next;
        }
    }
    free(hash->buckets);
    free(hash);
}
 
struct hash_element *
hash_lookup_fast(struct hash *hash,
                 struct hash_bucket *bucket,
                 const void *key,
                 uint32_t hv)
{
    struct hash_element *he;
    struct hash_element *prev = NULL;
 
    he = bucket->list;
 
    while (he)
    {
        if (hv == he->hash_value && (*hash->compare_function)(key, he->key))
        {
            /* move to head of list */
            if (prev)
            {
                prev->next = he->next;
                he->next = bucket->list;
                bucket->list = he;
            }
            return he;
        }
        prev = he;
        he = he->next;
    }
 
    return NULL;
}
 
bool
hash_remove_fast(struct hash *hash,
                 struct hash_bucket *bucket,
                 const void *key,
                 uint32_t hv)
{
    struct hash_element *he;
    struct hash_element *prev = NULL;
 
    he = bucket->list;
 
    while (he)
    {
        if (hv == he->hash_value && (*hash->compare_function)(key, he->key))
        {
            if (prev)
            {
                prev->next = he->next;
            }
            else
            {
                bucket->list = he->next;
            }
            free(he);
            --hash->n_elements;
            return true;
        }
        prev = he;
        he = he->next;
    }
    return false;
}
 
bool
hash_add(struct hash *hash, const void *key, void *value, bool replace)
{
    uint32_t hv;
    struct hash_bucket *bucket;
    struct hash_element *he;
    bool ret = false;
 
    hv = hash_value(hash, key);
    bucket = &hash->buckets[hv & hash->mask];
 
    if ((he = hash_lookup_fast(hash, bucket, key, hv))) /* already exists? */
    {
        if (replace)
        {
            he->value = value;
            ret = true;
        }
    }
    else
    {
        hash_add_fast(hash, bucket, key, hv, value);
        ret = true;
    }
 
    return ret;
}
 
void
hash_remove_by_value(struct hash *hash, void *value)
{
    struct hash_iterator hi;
    struct hash_element *he;
 
    hash_iterator_init(hash, &hi);
    while ((he = hash_iterator_next(&hi)))
    {
        if (he->value == value)
        {
            hash_iterator_delete_element(&hi);
        }
    }
    hash_iterator_free(&hi);
}
 
static void
hash_remove_marked(struct hash *hash, struct hash_bucket *bucket)
{
    struct hash_element *prev = NULL;
    struct hash_element *he = bucket->list;
 
    while (he)
    {
        if (!he->key) /* marked? */
        {
            struct hash_element *newhe;
            if (prev)
            {
                newhe = prev->next = he->next;
            }
            else
            {
                newhe = bucket->list = he->next;
            }
            free(he);
            --hash->n_elements;
            he = newhe;
        }
        else
        {
            prev = he;
            he = he->next;
        }
    }
}
 
void
hash_iterator_init_range(struct hash *hash,
                         struct hash_iterator *hi,
                         int start_bucket,
                         int end_bucket)
{
    if (end_bucket > hash->n_buckets)
    {
        end_bucket = hash->n_buckets;
    }
 
    ASSERT(start_bucket >= 0 && start_bucket <= end_bucket);
 
    hi->hash = hash;
    hi->elem = NULL;
    hi->bucket = NULL;
    hi->last = NULL;
    hi->bucket_marked = false;
    hi->bucket_index_start = start_bucket;
    hi->bucket_index_end = end_bucket;
    hi->bucket_index = hi->bucket_index_start - 1;
}
 
void
hash_iterator_init(struct hash *hash,
                   struct hash_iterator *hi)
{
    hash_iterator_init_range(hash, hi, 0, hash->n_buckets);
}
 
static inline void
hash_iterator_lock(struct hash_iterator *hi, struct hash_bucket *b)
{
    hi->bucket = b;
    hi->last = NULL;
    hi->bucket_marked = false;
}
 
static inline void
hash_iterator_unlock(struct hash_iterator *hi)
{
    if (hi->bucket)
    {
        if (hi->bucket_marked)
        {
            hash_remove_marked(hi->hash, hi->bucket);
            hi->bucket_marked = false;
        }
        hi->bucket = NULL;
        hi->last = NULL;
    }
}
 
static inline void
hash_iterator_advance(struct hash_iterator *hi)
{
    hi->last = hi->elem;
    hi->elem = hi->elem->next;
}
 
void
hash_iterator_free(struct hash_iterator *hi)
{
    hash_iterator_unlock(hi);
}
 
struct hash_element *
hash_iterator_next(struct hash_iterator *hi)
{
    struct hash_element *ret = NULL;
    if (hi->elem)
    {
        ret = hi->elem;
        hash_iterator_advance(hi);
    }
    else
    {
        while (++hi->bucket_index < hi->bucket_index_end)
        {
            struct hash_bucket *b;
            hash_iterator_unlock(hi);
            b = &hi->hash->buckets[hi->bucket_index];
            if (b->list)
            {
                hash_iterator_lock(hi, b);
                hi->elem = b->list;
                if (hi->elem)
                {
                    ret = hi->elem;
                    hash_iterator_advance(hi);
                    break;
                }
            }
        }
    }
    return ret;
}
 
void
hash_iterator_delete_element(struct hash_iterator *hi)
{
    ASSERT(hi->last);
    hi->last->key = NULL;
    hi->bucket_marked = true;
}
 
 
/*
 * --------------------------------------------------------------------
 * hash() -- hash a variable-length key into a 32-bit value
 * k     : the key (the unaligned variable-length array of bytes)
 * len   : the length of the key, counting by bytes
 * level : can be any 4-byte value
 * Returns a 32-bit value.  Every bit of the key affects every bit of
 * the return value.  Every 1-bit and 2-bit delta achieves avalanche.
 * About 36+6len instructions.
 *
 * The best hash table sizes are powers of 2.  There is no need to do
 * mod a prime (mod is sooo slow!).  If you need less than 32 bits,
 * use a bitmask.  For example, if you need only 10 bits, do
 * h = (h & hashmask(10));
 * In which case, the hash table should have hashsize(10) elements.
 *
 * If you are hashing n strings (uint8_t **)k, do it like this:
 * for (i=0, h=0; i<n; ++i) h = hash( k[i], len[i], h);
 *
 * By Bob Jenkins, 1996.  bob_jenkins@burtleburtle.net.  You may use this
 * code any way you wish, private, educational, or commercial.  It's free.
 *
 * See http://burlteburtle.net/bob/hash/evahash.html
 * Use for hash table lookup, or anything where one collision in 2^32 is
 * acceptable.  Do NOT use for cryptographic purposes.
 *
 * --------------------------------------------------------------------
 *
 * mix -- mix 3 32-bit values reversibly.
 * For every delta with one or two bit set, and the deltas of all three
 * high bits or all three low bits, whether the original value of a,b,c
 * is almost all zero or is uniformly distributed,
 * If mix() is run forward or backward, at least 32 bits in a,b,c
 * have at least 1/4 probability of changing.
 * If mix() is run forward, every bit of c will change between 1/3 and
 * 2/3 of the time.  (Well, 22/100 and 78/100 for some 2-bit deltas.)
 * mix() was built out of 36 single-cycle latency instructions in a
 * structure that could supported 2x parallelism, like so:
 *    a -= b;
 *    a -= c; x = (c>>13);
 *    b -= c; a ^= x;
 *    b -= a; x = (a<<8);
 *    c -= a; b ^= x;
 *    c -= b; x = (b>>13);
 *    ...
 * Unfortunately, superscalar Pentiums and Sparcs can't take advantage
 * of that parallelism.  They've also turned some of those single-cycle
 * latency instructions into multi-cycle latency instructions.  Still,
 * this is the fastest good hash I could find.  There were about 2^^68
 * to choose from.  I only looked at a billion or so.
 *
 * James Yonan Notes:
 *
 * This function is faster than it looks, and appears to be
 * appropriate for our usage in OpenVPN which is primarily
 * for hash-table based address lookup (IPv4, IPv6, and Ethernet MAC).
 * NOTE: This function is never used for cryptographic purposes, only
 * to produce evenly-distributed indexes into hash tables.
 *
 * Benchmark results: 11.39 machine cycles per byte on a P2 266Mhz,
 *                   and 12.1 machine cycles per byte on a
 *                   2.2 Ghz P4 when hashing a 6 byte string.
 * --------------------------------------------------------------------
 */
 
#define mix(a, b, c)               \
    {                                \
        a -= b; a -= c; a ^= (c>>13);  \
        b -= c; b -= a; b ^= (a<<8);   \
        c -= a; c -= b; c ^= (b>>13);  \
        a -= b; a -= c; a ^= (c>>12);  \
        b -= c; b -= a; b ^= (a<<16);  \
        c -= a; c -= b; c ^= (b>>5);   \
        a -= b; a -= c; a ^= (c>>3);   \
        b -= c; b -= a; b ^= (a<<10);  \
        c -= a; c -= b; c ^= (b>>15);  \
    }
 
uint32_t
hash_func(const uint8_t *k, uint32_t length, uint32_t initval)
{
    uint32_t a, b, c, len;
 
    /* Set up the internal state */
    len = length;
    a = b = 0x9e3779b9;      /* the golden ratio; an arbitrary value */
    c = initval;             /* the previous hash value */
 
    /*---------------------------------------- handle most of the key */
    while (len >= 12)
    {
        a += (k[0] + ((uint32_t) k[1] << 8)
              + ((uint32_t) k[2] << 16)
              + ((uint32_t) k[3] << 24));
        b += (k[4] + ((uint32_t) k[5] << 8)
              + ((uint32_t) k[6] << 16)
              + ((uint32_t) k[7] << 24));
        c += (k[8] + ((uint32_t) k[9] << 8)
              + ((uint32_t) k[10] << 16)
              + ((uint32_t) k[11] << 24));
        mix(a, b, c);
        k += 12;
        len -= 12;
    }
 
    /*------------------------------------- handle the last 11 bytes */
    c += length;
    switch (len)            /* all the case statements fall through */
    {
        case 11:
            c += ((uint32_t) k[10] << 24);
 
        case 10:
            c += ((uint32_t) k[9] << 16);
 
        case 9:
            c += ((uint32_t) k[8] << 8);
 
        /* the first byte of c is reserved for the length */
        case 8:
            b += ((uint32_t) k[7] << 24);
 
        case 7:
            b += ((uint32_t) k[6] << 16);
 
        case 6:
            b += ((uint32_t) k[5] << 8);
 
        case 5:
            b += k[4];
 
        case 4:
            a += ((uint32_t) k[3] << 24);
 
        case 3:
            a += ((uint32_t) k[2] << 16);
 
        case 2:
            a += ((uint32_t) k[1] << 8);
 
        case 1:
            a += k[0];
            /* case 0: nothing left to add */
    }
    mix(a, b, c);
    /*-------------------------------------- report the result */
    return c;
}