text: /*
   * Copyright (c) 2010-2013 BitTorrent, Inc.
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
   * THE SOFTWARE.
   */
  
  #include "utp_hash.h"
  #include "utp_types.h"
  
  #define LIBUTP_HASH_UNUSED ((utp_link_t)-1)
  
  #ifdef STRICT_ALIGN
  inline uint32 Read32(const void *p)
  {
  	uint32 tmp;
  	memcpy(&tmp, p, sizeof tmp);
  	return tmp;
  }
  
  #else
  inline uint32 Read32(const void *p) { return *(uint32*)p; }
  #endif
  
  
  // Get the amount of memory required for the hash parameters and the bucket set
  // Waste a space for an unused bucket in order to ensure the following managed memory have 32-bit aligned addresses
  // TODO:  make this 64-bit clean
  #define BASE_SIZE(bc) (sizeof(utp_hash_t) + sizeof(utp_link_t) * ((bc) + 1))
  
  // Get a pointer to the base of the structure array managed by the hash table
  #define get_bep(h) ((byte*)(h)) + BASE_SIZE((h)->N)
  
  // Get the address of the information associated with a specific structure in the array,
  // given the address of the base of the structure.
  // This assumes a utp_link_t link member is at the end of the structure.
  // Given compilers filling out the memory to a 32-bit clean value, this may mean that
  // the location named in the structure may not be the location actually used by the hash table,
  // since the compiler may have padded the end of the structure with 2 bytes after the utp_link_t member.
  // TODO: this macro should not require that the variable pointing at the hash table be named 'hash'
  #define ptr_to_link(p) (utp_link_t *) (((byte *) (p)) + hash->E - sizeof(utp_link_t))
  
  // Calculate how much to allocate for a hash table with bucket count, total size, and structure count
  // TODO:  make this 64-bit clean
  #define ALLOCATION_SIZE(bc, ts, sc) (BASE_SIZE((bc)) + (ts) * (sc))
  
  utp_hash_t *utp_hash_create(int N, int key_size, int total_size, int initial, utp_hash_compute_t hashfun, utp_hash_equal_t compfun)
  {
  	// Must have odd number of hash buckets (prime number is best)
  	assert(N % 2);
  	// Ensure structures will be at aligned memory addresses
  	// TODO:  make this 64-bit clean
  	assert(0 == (total_size % 4));
  
  	int size = ALLOCATION_SIZE(N, total_size, initial);
  	utp_hash_t *hash = (utp_hash_t *) malloc( size );
  	memset( hash, 0, size );
  
  	for (int i = 0; i < N + 1; ++i)
  		hash->inits[i] = LIBUTP_HASH_UNUSED;
  	hash->N = N;
  	hash->K = key_size;
  	hash->E = total_size;
  	hash->hash_compute = hashfun;
  	hash->hash_equal = compfun;
  	hash->allocated = initial;
  	hash->count = 0;
  	hash->used = 0;
  	hash->free = LIBUTP_HASH_UNUSED;
  	return hash;
  }
  
  uint utp_hash_mem(const void *keyp, size_t keysize)
  {
  	uint hash = 0;
  	uint n = keysize;
  	while (n >= 4) {
  		hash ^= Read32(keyp);
  		keyp = (byte*)keyp + sizeof(uint32);
  		hash = (hash << 13) | (hash >> 19);
  		n -= 4;
  	}
  	while (n != 0) {
  		hash ^= *(byte*)keyp;
  		keyp = (byte*)keyp + sizeof(byte);
  		hash = (hash << 8) | (hash >> 24);
  		n--;
  	}
  	return hash;
  }
  
  static uint utp_hash_mkidx(utp_hash_t *hash, const void *keyp)
  {
  	// Generate a key from the hash
  	return hash->hash_compute(keyp, hash->K) % hash->N;
  }
  
  static inline bool compare(byte *a, byte *b,int n)
  {
  	assert(n >= 4);
  	if (Read32(a) != Read32(b)) return false;
  	return memcmp(a+4, b+4, n-4) == 0;
  }
  
  #define COMPARE(h,k1,k2,ks) (((h)->hash_equal) ? (h)->hash_equal((void*)k1,(void*)k2,ks) : compare(k1,k2,ks))
  
  // Look-up a key in the hash table.
  // Returns NULL if not found
  void *utp_hash_lookup(utp_hash_t *hash, const void *key)
  {
  	utp_link_t idx = utp_hash_mkidx(hash, key);
  
  	// base pointer
  	byte *bep = get_bep(hash);
  
  	utp_link_t cur = hash->inits[idx];
  	while (cur != LIBUTP_HASH_UNUSED) {
  		byte *key2 = bep + (cur * hash->E);
  		if (COMPARE(hash, (byte*)key, key2, hash->K))
  			return key2;
  		cur = *ptr_to_link(key2);
  	}
  
  	return NULL;
  }
  
  // Add a new element to the hash table.
  // Returns a pointer to the new element.
  // This assumes the element is not already present!
  void *utp_hash_add(utp_hash_t **hashp, const void *key)
  {
  	//Allocate a new entry
  	byte *elemp;
  	utp_link_t elem;
  	utp_hash_t *hash = *hashp;
  	utp_link_t idx = utp_hash_mkidx(hash, key);
  
  	if ((elem=hash->free) == LIBUTP_HASH_UNUSED) {
  		utp_link_t all = hash->allocated;
  		if (hash->used == all) {
  			utp_hash_t *nhash;
  			if (all <= (LIBUTP_HASH_UNUSED/2)) {
  				all *= 2;
  			} else if (all != LIBUTP_HASH_UNUSED) {
  				all  = LIBUTP_HASH_UNUSED;
  			} else {
  				// too many items! can't grow!
  				assert(0);
  				return NULL;
  			}
  			// otherwise need to allocate.
  			nhash = (utp_hash_t*)realloc(hash, ALLOCATION_SIZE(hash->N, hash->E, all));
  			if (!nhash) {
  				// out of memory (or too big to allocate)
  				assert(nhash);
  				return NULL;
  			}
  			hash = *hashp = nhash;
  			hash->allocated = all;
  		}
  
  		elem = hash->used++;
  		elemp = get_bep(hash) + elem * hash->E;
  	} else {
  		elemp = get_bep(hash) + elem * hash->E;
  		hash->free = *ptr_to_link(elemp);
  	}
  
  	*ptr_to_link(elemp) = hash->inits[idx];
  	hash->inits[idx] = elem;
  	hash->count++;
  
  	// copy key into it
  	memcpy(elemp, key, hash->K);
  	return elemp;
  }
  
  // Delete an element from the utp_hash_t
  // Returns a pointer to the already deleted element.
  void *utp_hash_del(utp_hash_t *hash, const void *key)
  {
  	utp_link_t idx = utp_hash_mkidx(hash, key);
  
  	// base pointer
  	byte *bep = get_bep(hash);
  
  	utp_link_t *curp = &hash->inits[idx];
  	utp_link_t cur;
  	while ((cur=*curp) != LIBUTP_HASH_UNUSED) {
  		byte *key2 = bep + (cur * hash->E);
  		if (COMPARE(hash,(byte*)key,(byte*)key2, hash->K )) {
  			// found an item that matched. unlink it
  			*curp = *ptr_to_link(key2);
  			// Insert into freelist
  			*ptr_to_link(key2) = hash->free;
  			hash->free = cur;
  			hash->count--;
  			return key2;
  		}
  		curp = ptr_to_link(key2);
  	}
  
  	return NULL;
  }
  
  void *utp_hash_iterate(utp_hash_t *hash, utp_hash_iterator_t *iter)
  {
  	utp_link_t elem;
  
  	if ((elem=iter->elem) == LIBUTP_HASH_UNUSED) {
  		// Find a bucket with an element
  		utp_link_t buck = iter->bucket + 1;
  		for(;;) {
  			if (buck >= hash->N)
  				return NULL;
  			if ((elem = hash->inits[buck]) != LIBUTP_HASH_UNUSED)
  				break;
  			buck++;
  		}
  		iter->bucket = buck;
  	}
  
  	byte *elemp = get_bep(hash) + (elem * hash->E);
  	iter->elem = *ptr_to_link(elemp);
  	return elemp;
  }
  
  void utp_hash_free_mem(utp_hash_t* hash)
  {
  	free(hash);
  }
  