// Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.

//

// 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

//

//     https://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 <assert.h>

#include <limits.h>

#include <string.h>

#include <openssl/mem.h>

#include "../internal.h"

#include "../mem_internal.h"

#include "internal.h"

BSSL_NAMESPACE_BEGIN

// kMinNumBuckets is the minimum size of the buckets array in an |_LHASH|.

static const size_t kMinNumBuckets = 16;

// kMaxAverageChainLength contains the maximum, average chain length. When the

// average chain length exceeds this value, the hash table will be resized.

static const size_t kMaxAverageChainLength = 2;

static const size_t kMinAverageChainLength = 1;

// lhash_item_st is an element of a hash chain. It points to the opaque data

// for this element and to the next item in the chain. The linked-list is NULL

// terminated.

typedef struct lhash_item_st {

  void *data;

  struct lhash_item_st *next;

  // hash contains the cached, hash value of |data|.

  uint32_t hash;

} LHASH_ITEM;

struct lhash_st {

  // num_items contains the total number of items in the hash table.

  size_t num_items;

  // buckets is an array of |num_buckets| pointers. Each points to the head of

  // a chain of LHASH_ITEM objects that have the same hash value, mod

  // |num_buckets|.

  LHASH_ITEM **buckets;

  // num_buckets contains the length of |buckets|. This value is always >=

  // kMinNumBuckets.

  size_t num_buckets;

  // callback_depth contains the current depth of |lh_doall| or |lh_doall_arg|

  // calls. If non-zero then this suppresses resizing of the |buckets| array,

  // which would otherwise disrupt the iteration.

  unsigned callback_depth;

  lhash_cmp_func comp;

  lhash_hash_func hash;

};

_LHASH *OPENSSL_lh_new(lhash_hash_func hash, lhash_cmp_func comp) {

  _LHASH *ret = NewZeroed<_LHASH>();

  if (ret == nullptr) {

    return nullptr;

  }

  ret->num_buckets = kMinNumBuckets;

  ret->buckets = reinterpret_cast<LHASH_ITEM **>(

      OPENSSL_calloc(ret->num_buckets, sizeof(LHASH_ITEM *)));

  if (ret->buckets == nullptr) {

    Delete(ret);

    return nullptr;

  }

  ret->comp = comp;

  ret->hash = hash;

  return ret;

}

void OPENSSL_lh_free(_LHASH *lh) {

  if (lh == nullptr) {

    return;

  }

  for (size_t i = 0; i < lh->num_buckets; i++) {

    LHASH_ITEM *next;

    for (LHASH_ITEM *n = lh->buckets[i]; n != nullptr; n = next) {

      next = n->next;

      Delete(n);

    }

  }

  OPENSSL_free(lh->buckets);

  Delete(lh);

}

size_t OPENSSL_lh_num_items(const _LHASH *lh) { return lh->num_items; }

// get_next_ptr_and_hash returns a pointer to the pointer that points to the

// item equal to |data|. In other words, it searches for an item equal to |data|

// and, if it's at the start of a chain, then it returns a pointer to an

// element of |lh->buckets|, otherwise it returns a pointer to the |next|

// element of the previous item in the chain. If an element equal to |data| is

// not found, it returns a pointer that points to a NULL pointer. If |out_hash|

// is not NULL, then it also puts the hash value of |data| in |*out_hash|.

static LHASH_ITEM **get_next_ptr_and_hash(const _LHASH *lh, uint32_t *out_hash,

                                          const void *data,

                                          lhash_hash_func_helper call_hash_func,

                                          lhash_cmp_func_helper call_cmp_func) {

  const uint32_t hash = call_hash_func(lh->hash, data);

  if (out_hash != nullptr) {

    *out_hash = hash;

  }

  LHASH_ITEM **ret = &lh->buckets[hash % lh->num_buckets];

  for (LHASH_ITEM *cur = *ret; cur != nullptr; cur = *ret) {

    if (call_cmp_func(lh->comp, cur->data, data) == 0) {

      break;

    }

    ret = &cur->next;

  }

  return ret;

}

// get_next_ptr_by_key behaves like |get_next_ptr_and_hash| but takes a key

// which may be a different type from the values stored in |lh|.

static LHASH_ITEM **get_next_ptr_by_key(const _LHASH *lh, const void *key,

                                        uint32_t key_hash,

                                        int (*cmp_key)(const void *key,

                                                       const void *value)) {

  LHASH_ITEM **ret = &lh->buckets[key_hash % lh->num_buckets];

  for (LHASH_ITEM *cur = *ret; cur != nullptr; cur = *ret) {

    if (cmp_key(key, cur->data) == 0) {

      break;

    }

    ret = &cur->next;

  }

  return ret;

}

void *OPENSSL_lh_retrieve(const _LHASH *lh, const void *data,

                          lhash_hash_func_helper call_hash_func,

                          lhash_cmp_func_helper call_cmp_func) {

  LHASH_ITEM **next_ptr =

      get_next_ptr_and_hash(lh, nullptr, data, call_hash_func, call_cmp_func);

  return *next_ptr == nullptr ? nullptr : (*next_ptr)->data;

}

void *OPENSSL_lh_retrieve_key(const _LHASH *lh, const void *key,

                              uint32_t key_hash,

                              int (*cmp_key)(const void *key,

                                             const void *value)) {

  LHASH_ITEM **next_ptr = get_next_ptr_by_key(lh, key, key_hash, cmp_key);

  return *next_ptr == nullptr ? nullptr : (*next_ptr)->data;

}

// lh_rebucket allocates a new array of |new_num_buckets| pointers and

// redistributes the existing items into it before making it |lh->buckets| and

// freeing the old array.

static void lh_rebucket(_LHASH *lh, const size_t new_num_buckets) {

  LHASH_ITEM **new_buckets, *cur, *next;

  size_t i, alloc_size;

  alloc_size = sizeof(LHASH_ITEM *) * new_num_buckets;

  if (alloc_size / sizeof(LHASH_ITEM *) != new_num_buckets) {

    return;

  }

  new_buckets = reinterpret_cast<LHASH_ITEM **>(OPENSSL_zalloc(alloc_size));

  if (new_buckets == nullptr) {

    return;

  }

  for (i = 0; i < lh->num_buckets; i++) {

    for (cur = lh->buckets[i]; cur != nullptr; cur = next) {

      const size_t new_bucket = cur->hash % new_num_buckets;

      next = cur->next;

      cur->next = new_buckets[new_bucket];

      new_buckets[new_bucket] = cur;

    }

  }

  OPENSSL_free(lh->buckets);

  lh->num_buckets = new_num_buckets;

  lh->buckets = new_buckets;

}

// lh_maybe_resize resizes the |buckets| array if needed.

static void lh_maybe_resize(_LHASH *lh) {

  size_t avg_chain_length;

  if (lh->callback_depth > 0) {

    // Don't resize the hash if we are currently iterating over it.

    return;

  }

  assert(lh->num_buckets >= kMinNumBuckets);

  avg_chain_length = lh->num_items / lh->num_buckets;

  if (avg_chain_length > kMaxAverageChainLength) {

    const size_t new_num_buckets = lh->num_buckets * 2;

    if (new_num_buckets > lh->num_buckets) {

      lh_rebucket(lh, new_num_buckets);

    }

  } else if (avg_chain_length < kMinAverageChainLength &&

             lh->num_buckets > kMinNumBuckets) {

    size_t new_num_buckets = lh->num_buckets / 2;

    if (new_num_buckets < kMinNumBuckets) {

      new_num_buckets = kMinNumBuckets;

    }

    lh_rebucket(lh, new_num_buckets);

  }

}

int OPENSSL_lh_insert(_LHASH *lh, void **old_data, void *data,

                      lhash_hash_func_helper call_hash_func,

                      lhash_cmp_func_helper call_cmp_func) {

  uint32_t hash;

  LHASH_ITEM **next_ptr, *item;

  *old_data = nullptr;

  next_ptr =

      get_next_ptr_and_hash(lh, &hash, data, call_hash_func, call_cmp_func);

  if (*next_ptr != nullptr) {

    // An element equal to |data| already exists in the hash table. It will be

    // replaced.

    *old_data = (*next_ptr)->data;

    (*next_ptr)->data = data;

    return 1;

  }

  // An element equal to |data| doesn't exist in the hash table yet.

  item = New<LHASH_ITEM>();

  if (item == nullptr) {

    return 0;

  }

  item->data = data;

  item->hash = hash;

  item->next = nullptr;

  *next_ptr = item;

  lh->num_items++;

  lh_maybe_resize(lh);

  return 1;

}

void *OPENSSL_lh_delete(_LHASH *lh, const void *data,

                        lhash_hash_func_helper call_hash_func,

                        lhash_cmp_func_helper call_cmp_func) {

  LHASH_ITEM **next_ptr, *item, *ret;

  next_ptr =

      get_next_ptr_and_hash(lh, nullptr, data, call_hash_func, call_cmp_func);

  if (*next_ptr == nullptr) {

    // No such element.

    return nullptr;

  }

  item = *next_ptr;

  *next_ptr = item->next;

  ret = reinterpret_cast<LHASH_ITEM *>(item->data);

  Delete(item);

  lh->num_items--;

  lh_maybe_resize(lh);

  return ret;

}

void OPENSSL_lh_doall_arg(_LHASH *lh, void (*func)(void *, void *), void *arg) {

  if (lh == nullptr) {

    return;

  }

  if (lh->callback_depth < UINT_MAX) {

    // |callback_depth| is a saturating counter.

    lh->callback_depth++;

  }

  for (size_t i = 0; i < lh->num_buckets; i++) {

    LHASH_ITEM *next;

    for (LHASH_ITEM *cur = lh->buckets[i]; cur != nullptr; cur = next) {

      next = cur->next;

      func(cur->data, arg);

    }

  }

  if (lh->callback_depth < UINT_MAX) {

    lh->callback_depth--;

  }

  // The callback may have added or removed elements and the non-zero value of

  // |callback_depth| will have suppressed any resizing. Thus any needed

  // resizing is done here.

  lh_maybe_resize(lh);

}

BSSL_NAMESPACE_END