/*

 * Copyright (c) 2013 Nicira, Inc.

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at:

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

#include <config.h>

#include "hindex.h"

#include "coverage.h"

static bool hindex_node_is_body(const struct hindex_node *);

static bool hindex_node_is_head(const struct hindex_node *);

static void hindex_resize(struct hindex *, size_t new_mask);

static size_t hindex_calc_mask(size_t capacity);

COVERAGE_DEFINE(hindex_pathological);

COVERAGE_DEFINE(hindex_expand);

COVERAGE_DEFINE(hindex_shrink);

COVERAGE_DEFINE(hindex_reserve);

/* Initializes 'hindex' as an empty hash index. */

void

hindex_init(struct hindex *hindex)

{

    hindex->buckets = &hindex->one;

    hindex->one = NULL;

    hindex->mask = 0;

    hindex->n_unique = 0;

}

/* Frees memory reserved by 'hindex'.  It is the client's responsibility to

 * free the nodes themselves, if necessary. */

void

hindex_destroy(struct hindex *hindex)

{

    if (hindex && hindex->buckets != &hindex->one) {

        free(hindex->buckets);

    }

}

/* Removes all node from 'hindex', leaving it ready to accept more nodes.  Does

 * not free memory allocated for 'hindex'.

 *

 * This function is appropriate when 'hindex' will soon have about as many

 * elements as it before.  If 'hindex' will likely have fewer elements than

 * before, use hindex_destroy() followed by hindex_clear() to save memory and

 * iteration time. */

void

hindex_clear(struct hindex *hindex)

{

    if (hindex->n_unique > 0) {

        hindex->n_unique = 0;

        memset(hindex->buckets, 0,

               (hindex->mask + 1) * sizeof *hindex->buckets);

    }

}

/* Exchanges hash indexes 'a' and 'b'. */

void

hindex_swap(struct hindex *a, struct hindex *b)

{

    struct hindex tmp = *a;

    *a = *b;

    *b = tmp;

    hindex_moved(a);

    hindex_moved(b);

}

/* Adjusts 'hindex' to compensate for having moved position in memory (e.g. due

 * to realloc()). */

void

hindex_moved(struct hindex *hindex)

{

    if (!hindex->mask) {

        hindex->buckets = &hindex->one;

    }

}

/* Expands 'hindex', if necessary, to optimize the performance of searches. */

void

hindex_expand(struct hindex *hindex)

{

    size_t new_mask = hindex_calc_mask(hindex->n_unique);

    if (new_mask > hindex->mask) {

        COVERAGE_INC(hindex_expand);

        hindex_resize(hindex, new_mask);

    }

}

/* Shrinks 'hindex', if necessary, to optimize the performance of iteration. */

void

hindex_shrink(struct hindex *hindex)

{

    size_t new_mask = hindex_calc_mask(hindex->n_unique);

    if (new_mask < hindex->mask) {

        COVERAGE_INC(hindex_shrink);

        hindex_resize(hindex, new_mask);

    }

}

/* Expands 'hindex', if necessary, to optimize the performance of searches when

 * it has up to 'n' unique hashes.  (But iteration will be slow in a hash index

 * whose allocated capacity is much higher than its current number of

 * nodes.)  */

void

hindex_reserve(struct hindex *hindex, size_t n)

{

    size_t new_mask = hindex_calc_mask(n);

    if (new_mask > hindex->mask) {

        COVERAGE_INC(hindex_reserve);

        hindex_resize(hindex, new_mask);

    }

}

/* Inserts 'node', with the given 'hash', into 'hindex'.  Never automatically

 * expands 'hindex' (use hindex_insert() instead if you want that). */

void

hindex_insert_fast(struct hindex *hindex,

                   struct hindex_node *node, size_t hash)

{

    struct hindex_node *head = hindex_node_with_hash(hindex, hash);

    if (head) {

        /* 'head' is an existing head with hash == 'hash'.

         * Insert 'node' as a body node just below 'head'. */

        node->s = head->s;

        node->d = head;

        if (node->s) {

            node->s->d = node;

        }

        head->s = node;

    } else {

        /* No existing node has hash 'hash'.  Insert 'node' as a new head in

         * its bucket. */

        struct hindex_node **bucket = &hindex->buckets[hash & hindex->mask];

        node->s = NULL;

        node->d = *bucket;

        *bucket = node;

        hindex->n_unique++;

    }

    node->hash = hash;

}

/* Inserts 'node', with the given 'hash', into 'hindex', and expands 'hindex'

 * if necessary to optimize search performance. */

void

hindex_insert(struct hindex *hindex, struct hindex_node *node, size_t hash)

{

    hindex_insert_fast(hindex, node, hash);

    if (hindex->n_unique / 2 > hindex->mask) {

        hindex_expand(hindex);

    }

}

/* Removes 'node' from 'hindex'.  Does not shrink the hash index; call

 * hindex_shrink() directly if desired. */

void

hindex_remove(struct hindex *hindex, struct hindex_node *node)

{

    if (!hindex_node_is_head(node)) {

        node->d->s = node->s;

        if (node->s) {

            node->s->d = node->d;

        }

    } else {

        struct hindex_node **head;

        for (head = &hindex->buckets[node->hash & hindex->mask];

             (*head)->hash != node->hash;

             head = &(*head)->d)

        {

            continue;

        }

        if (node->s) {

            *head = node->s;

            node->s->d = node->d;

        } else {

            *head = node->d;

            hindex->n_unique--;

        }

    }

}

/* Helper functions. */

/* Returns true if 'node', which must be inserted into an hindex, is a "body"

 * node, that is, it is not reachable from a bucket by following zero or more

 * 'd' pointers.  Returns false otherwise. */

static bool

hindex_node_is_body(const struct hindex_node *node)

{

    return node->d && node->d->hash == node->hash;

}

/* Returns true if 'node', which must be inserted into an hindex, is a "head"

 * node, that is, if it is reachable from a bucket by following zero or more

 * 'd' pointers.  Returns false if 'node' is a body node (and therefore one

 * must follow at least one 's' pointer to reach it). */

static bool

hindex_node_is_head(const struct hindex_node *node)

{

    return !hindex_node_is_body(node);

}

/* Reallocates 'hindex''s array of buckets to use bitwise mask 'new_mask'. */

static void

hindex_resize(struct hindex *hindex, size_t new_mask)

{

    struct hindex tmp;

    size_t i;

    ovs_assert(is_pow2(new_mask + 1));

    ovs_assert(new_mask != SIZE_MAX);

    hindex_init(&tmp);

    if (new_mask) {

        tmp.buckets = xmalloc(sizeof *tmp.buckets * (new_mask + 1));

        tmp.mask = new_mask;

        for (i = 0; i <= tmp.mask; i++) {

            tmp.buckets[i] = NULL;

        }

    }

    for (i = 0; i <= hindex->mask; i++) {

        struct hindex_node *node, *next;

        int count;

        count = 0;

        for (node = hindex->buckets[i]; node; node = next) {

            struct hindex_node **head = &tmp.buckets[node->hash & tmp.mask];

            next = node->d;

            node->d = *head;

            *head = node;

            count++;

        }

        if (count > 5) {

            COVERAGE_INC(hindex_pathological);

        }

    }

    tmp.n_unique = hindex->n_unique;

    hindex_swap(hindex, &tmp);

    hindex_destroy(&tmp);

}

/* Returns the bitwise mask to use in struct hindex to support 'capacity'

 * hindex_nodes with unique hashes. */

static size_t

hindex_calc_mask(size_t capacity)

{

    size_t mask = capacity / 2;

    mask |= mask >> 1;

    mask |= mask >> 2;

    mask |= mask >> 4;

    mask |= mask >> 8;

    mask |= mask >> 16;

#if SIZE_MAX > UINT32_MAX

    mask |= mask >> 32;

#endif

    /* If we need to dynamically allocate buckets we might as well allocate at

     * least 4 of them. */

    mask |= (mask & 1) << 1;

    return mask;

}

/* Returns the head node in 'hindex' with the given 'hash'.  'hindex' must

 * contain a head node with the given hash. */

static struct hindex_node *

hindex_head_node(const struct hindex *hindex, size_t hash)

{

    struct hindex_node *node = hindex->buckets[hash & hindex->mask];

    while (node->hash != hash) {

        node = node->d;

    }

    return node;

}

static struct hindex_node *

hindex_next__(const struct hindex *hindex, size_t start)

{

    size_t i;

    for (i = start; i <= hindex->mask; i++) {

        struct hindex_node *node = hindex->buckets[i];

        if (node) {

            return node;

        }

    }

    return NULL;

}

/* Returns the first node in 'hindex', in arbitrary order, or a null pointer if

 * 'hindex' is empty. */

struct hindex_node *

hindex_first(const struct hindex *hindex)

{

    return hindex_next__(hindex, 0);

}

/* Returns the next node in 'hindex' following 'node', in arbitrary order, or a

 * null pointer if 'node' is the last node in 'hindex'.

 *

 * If the hash index has been reallocated since 'node' was visited, some nodes

 * may be skipped or visited twice. */

struct hindex_node *

hindex_next(const struct hindex *hindex, const struct hindex_node *node)

{

    struct hindex_node *head;

    /* If there's a node with the same hash, return it. */

    if (node->s) {

        return node->s;

    }

    /* If there's another node in the same bucket, return it. */

    head = hindex_head_node(hindex, node->hash);

    if (head->d) {

        return head->d;

    }

    /* Return the first node in the next (or later) bucket. */

    return hindex_next__(hindex, (node->hash & hindex->mask) + 1);

}