C 在这种情况下，有可能生成最小完美哈希函数吗？

我想创建一个散列映射（或者其他结构，如果您有任何建议的话）来存储键值对。在创建映射的同时，所有键都将同时插入，但我不知道这些键将是什么（任意长度的字符串），直到运行时，我才需要创建映射

我正在解析这样的查询字符串

“x=100&name=bob&color=red&y=150”

（但是该字符串可以有无限数量的变量，变量可以有任意长度的名称）

我想对它进行一次解析，然后创建一个哈希映射，最好是最小的，并使用一个完美的哈希函数来满足线性存储需求。创建映射后，不会修改或删除值，也不会向映射中添加更多的键值对，因此整个映射实际上是一个常量。我假设一个变量在字符串中不会出现两次（即，

“x=1&x=2”

无效）

---

我正在用

C

编码，目前有一个函数可以使用，比如

get（“x”）

，它将返回字符串

“100”

，但每次它都会解析查询字符串，这需要

O（n）

时间。我想在第一次加载时对它进行一次解析，因为它是一个非常大的查询字符串，每个值都会被读取几次。即使我正在使用

C

，我也不需要

C

中的代码作为答案。伪代码，或者任何建议都会很棒

在你描述的内容中没有完美的散列。一个完美的散列将是原始输入。如果您保证您的数据将只包含某些内容（例如基于拉丁语的ASCII或仅包含某些键），那么您可以很好地进行散列，但是否完美？不可能。您还必须创建链接列表或向量哈希未命中机制。系统中的任何变量（如案例中的输入计数）都将使完美哈希概念无效

你想要的东西违反了数学定律

你可以达到接近O（1），但这里有一些未回答的问题。问题是:

为什么它必须是线性存储

表中的删除是否常见（您只指定在初始创建后不会添加键值对）

与散列的范围相比，表可能增长多大

与重复数据相比，插入的频率有多高

记忆是一个重要因素吗

虽然完美的散列是不可能的，但是如果你可以简单地拥有一个简单的链表，它的bucket大小至少是你潜在的唯一散列平均值的两个标准差，那么它就完全是学术性的了。它的内存很小（当然，相对而言，取决于总的潜在大小），易于删除，只要问题3的答案是“小得多”，它的查找时间就接近O（1）

下面应该让您开始，但我会让您决定使用哪种哈希算法

#include <stdlib.h>
#include <string.h>
#include <stdint.h>


// Dummy value type to test compile. Replace throughout 
#define YOUR_VALUE_T int

// See below where the charmap is
//#define HTABLE_USE_CHARMAP
// Maintain a true linked list that's manageable and iterateable
#define HTABLE_MAINTAIN_LIST
// Count lookup misses and such
#define HTABLE_KEEP_STATS
// Fast deletion = faster deletion but more memory consumption
//#define HTABLE_FAST_DELETES

#ifdef HTABLE_USE_CHARMAP
// This is used to quickly collapse the input from full 8-bit to the minimal character set of truely expected data.
// The idea here is to boil down the data. This should only be done if you're confident enough to develop a custom
// hashing algorithm for this particular known range
const char hashing_charmap[256] = {
   // Each data point that is unused (such as control characters or high 8-bit characters)
   // should be 0, while each used character should be represented with a unique sequential value (1, 2, 3, etc)
   // I'm not going to build this for you because it's very custom to your needs.
   // A chunk might look look like...
   /*
   0, 0, 0, 0, 17, 18, 19, 0, 0, 20, 21,
   */
};
#endif

static inline uint32_t hash_str(register const char* s, const size_t len) {
   register uint32_t hash = 5381; // hash seed here. This could be different depending on the actual algorithm chosen
   register char symbol;
   // This could be unrolled because we known string length as well.
   for (register size_t i=0; i < len; i++) {
      #ifdef HTABLE_USE_CHARMAP
      if (!(symbol = hash_charmap[s[i]]))
         continue;
      #else
      // Actually s[i] could simply be used (which would be faster) if no mapping is needed.
      symbol = s[i];
      #endif
      // True hash algorithm per-symbol operation here
      /*
      Keep in mind that certain algorithms are optimized for certain things.
      An example:
      Stock DJBX33A is very fast but effectively only represents the end of a long input. It's really meant for short inputs (like variable names)
      A MurmurHash or tuned FNV variant are likely to be a good picks since we've reduced symbol range and we are dealing with potential long inputs.
      It's also important to understand that the entire hash will likely not be used. Only the lower-end bits will be used
      (you'll see why in the actual functionality). If you're hashing algorithm is good though, this shouldn't matter because
      the distribution should be normal.
      I'll just use Jenkins one-at-a-time hash here (because it's easy)
      */
      hash += symbol;
      hash += (hash << 10);
      hash ^= (hash >> 6);
   }
   // Finialize jenkins one-at-a-time
   hash += (hash << 3);
   hash ^= (hash >> 11);
   hash += (hash << 15);
   return hash;
};


typedef struct _hash_entry {
   char* key;
   size_t key_len;
   uint32_t hash;
   // Whatever your value type is (likely a pointer to your own record or something)
   YOUR_VALUE_T value;
   // Internal linking maintains order.
   // If you don't need proper order maintentence, you don't need these
   #ifdef HTABLE_MAINTAIN_LIST
   struct _hash_entry* prev;
   struct _hash_entry* next;
   #endif

   #ifdef HTABLE_FAST_DELETES
   struct _hash_entry* bucket_prev;
   #endif
   // This is required for the occassional hash miss
   struct _hash_entry* bucket_next;
} hash_entry_t;


typedef struct _hash_table {
   // Counts
   size_t entry_count;
   uint32_t bucket_count;
   unsigned int growth_num;
   unsigned int growth_den;
   #ifdef HTABLE_KEEP_STATS
   // How many times we missed during lookup
   size_t misses;
   // (entry_count - used_buckets) tells you how many collisions there are (the lower the better)
   uint32_t used_buckets;
   #endif
   // Internal linking. Same conditions as in hash_entry_t so feel free to remove as necessary.
   #ifdef HTABLE_MAINTAIN_LIST
   hash_entry_t* first;
   hash_entry_t* last;
   #endif
   // Buckets, the soul of the hash table
   uint32_t hash_mask;
   hash_entry_t** buckets;
} hash_table_t;



// Creates a hash table
// size_hint - Tells to table how many buckets it should initially allocate.
//    If you know (for example) that you'll have about 500 entries, set it
//    to 500
// growth_num and growth_den - This is the ratio of how many entries to how
//    many buckets that you want to guarantee.
//    It's in two integers to avoid floating point math for speed.
//    The logic after an insertion is...
//       if (entry_count == growth_num * (bucket_count / growth_den)) then
//          grow the bucket array
//    For example, when growth_num is 4 and growth_den is 5...
//       (entry_count == 4 * (bucket_count / 5))
//   ...would be true when entry count is 80% of the bucket count
//    This can result in a greater than 1.0 ratio (such as 5/4 or something
//    like that) if you prefer. This would mean that there are less buckets
//    than there are entries, so collisions are guaranteed at that point, but
//    you would save on both memory and often a bucket expansion occurs (which
//    is costly during an insert operation).
static hash_table_t* htable_create(const size_t size_hint, const unsigned int growth_num, const unsigned int growth_den);
// Frees a hash table
static void htable_free(hash_table_t* table);
// Mostly used internally. You probably want htable_get(), htable_value(), or htable_exists()
static hash_entry_t* htable_find_entry(hash_table_t* table, const char* key, size_t key_len, uint32_t* hash, size_t* true_len);
// Get the pointer to a value stored in the table (or NULL on non-existant)
static YOUR_VALUE_T* htable_value(const hash_table_t* table, const char* key, size_t key_len);
// Get the value of an entry, or the default value if the entry doesn't exist
static YOUR_VALUE_T htable_get(const hash_table_t* table, const char* key, size_t key_len, const YOUR_VALUE_T default_value);
// Test for the existance of a value
static int htable_exists(const hash_table_t* table, const char* key, size_t key_len);
// Add a new entry (but don't update if it already exists). Returns NULL if it already exists
static hash_entry_t* htable_add(hash_table_t* table, const char* key, size_t key_len, YOUR_VALUE_T value);
// Update an entry OR add a a new entry it doesn't already exist
static hash_entry_t* htable_set(hash_table_t* table, const char* key, size_t key_len, YOUR_VALUE_T value);
// Update an entry but don't add a a new entry it doesn't already exist. Returns NULL if doesn't exist
static hash_entry_t* htable_update(hash_table_t* table, const char* key, size_t key_len, YOUR_VALUE_T value);
// Delete an entry. Returns 1 on success or 0 if the entry didn't exist
static int htable_delete(hash_table_t* table, const char* key, size_t key_len);
// Pack the table.
// This is here because...
// - If HTABLE_FAST_DELETES is set, and if you delete a bunch of entries, it's
//   possible that you can free up some memory by shrinking the bucket array.
//   You would have to call this manually to make that happen.
// - If HTABLE_FAST_DELETES is NOT set however, this get's called automatically
//   on each delete, so the buckets are guaranteed to be packed.
static void htable_pack(hash_table_t* table);



/*********************************\
Implementation...
\*********************************/
static hash_table_t* htable_create(const unsigned long size_hint, const unsigned int growth_num, const unsigned int growth_den) {
   hash_table_t* res = malloc(sizeof(hash_table_t));
   if (!res)
      return NULL;
   res->entry_count = 0;
   #ifdef HTABLE_MAINTAIN_LIST
   res->first = NULL;
   res->last = NULL;
   #endif

   #ifdef HTABLE_KEEP_STATS
   res->misses = 0; 
   res->used_buckets = 0;
   #endif
   if ((!growth_num) || (!growth_den)) {
      // Grow only when the entry count matches the bucket count
      res->growth_num = 1;
      res->growth_den = 1;
   } else {
      res->growth_num = growth_num;
      res->growth_den = growth_den;
   }
   /*
   For computational speed and simplicity we'll grow the bucket array exponentially.
   Not growing the buckets exponentially is possible but requires a different
   entry lookup mechanism (because hash & hash_mask would no longer work) and would 
   likely involve the modulas operator which is very slow. If memory is uber important
   however, this might be a good solution.
   */
   // We'll go ahead and assume it's a reasonably small table and only allocate 256 buckets.
   int bits = 8;
   if (size_hint) {
      unsigned long target = (size_hint * res->growth_den) / res->growth_num;
      // First check is to prevent overflow as it would be 0 when bits is 31 on a 32 bit system
      while ((1 << (bits + 1)) && ((1 << bits) < target))
         bits++;
   }
   res->bucket_count = 1 << bits;
   res->hash_mask = (1 << bits) - 1;
   if ((res->buckets = (hash_entry_t**)calloc(res->bucket_count, sizeof(hash_entry_t*))) == NULL) {
      free(res);
      return NULL;
   }
   memset(res->buckets, 0, sizeof(hash_entry_t*) * res->bucket_count);
   return res;
};

// Destroy a table
static void htable_free(hash_table_t* table) {
   hash_entry_t* entry;
   hash_entry_t* next;
   #ifdef HTABLE_MAINTAIN_LIST
      entry = table->first;
      while (entry) {
         next = entry->next;
         free(entry->key);
         free(entry);
         entry = next;
      }
   #else
      for (uint32_t i=0; i < table->bucket_count; i++) {
         entry = table->buckets[i];
         while (entry) {
            next = entry->bucket_next;
            free(entry->key);
            free(entry);
            entry = next;
         }
      }
   #endif
   free(table->buckets);
   free(table);
}

// Find an entry: (mostly used internally)
// returns NULL when the entry isn't found
static hash_entry_t* htable_find_entry(hash_table_t* table, const char* key, size_t key_len, uint32_t* hash, size_t* true_len) {
   if (!key_len)
      key_len = strlen(key);
   if (true_len != NULL)
      *true_len = key_len;
   uint32_t h = hash_str(key, key_len);
   if (hash != NULL)
      *hash = h;
   uint32_t bucket = h & table->hash_mask;
   // Best case is here is O(1) because table->buckets[bucket] would be the entry
   hash_entry_t* entry = table->buckets[bucket];
   // ... but if we miss, then the time increases to as much as O(n) where n is the number of entries in
   // the particular bucket (good hash + good ratio management means that n would usually be only 1)
   while ((entry) && ((entry->hash != h) || (entry->key_len != key_len) || (memcmp(entry->key, key, key_len)))) {
      #ifdef HTABLE_KEEP_STATS
      table->misses++;
      #endif
      entry = entry->bucket_next;
   }
   return entry;
}


// Insertion of entry into bucket. Used internally
static inline int _htable_bucket_insert(hash_entry_t** buckets, hash_entry_t* entry, const uint32_t hash_mask) {
   hash_entry_t* bentry;
   #ifdef HTABLE_FAST_DELETES
      entry->bucket_prev = NULL;
   #endif
   entry->bucket_next = NULL;
   uint32_t bidx = entry->hash & hash_mask;
   int res = 0;
   if ((bentry = buckets[bidx]) == NULL) {
      res = 1;
      buckets[bidx] = entry;
   } else {
      while (bentry->bucket_next)
         bentry = bentry->bucket_next;
      bentry->bucket_next = entry;
      #ifdef HTABLE_FAST_DELETES
         entry->bucket_prev = bentry;
      #endif
   }
   return res;
}

// Bucket array growing/shrinking. Used internally
static void _htable_adjust_as_needed(hash_table_t* table) {
   int change = (((table->bucket_count << 1) != 0) && (table->entry_count >= table->growth_num * (table->bucket_count / table->growth_den)));
   if (!change) {
      if ((table->bucket_count > (1 << 8)) && (table->entry_count < table->growth_num * ((table->bucket_count >> 1) / table->growth_den))) {
         change = -1;
      } else {
         return;
      }
   }
   uint32_t new_bucket_count = (change < 0) ? table->bucket_count >> 1 : table->bucket_count << 1;
   uint32_t new_hash_mask = new_bucket_count - 1;
   hash_entry_t** new_buckets = (hash_entry_t**)calloc(new_bucket_count, sizeof(hash_entry_t*));
   if (!new_buckets)
      return;
   memset(new_buckets, 0, new_bucket_count * sizeof(hash_entry_t*));
   #ifdef HTABLE_KEEP_STATS
      table->used_buckets = 0;
   #endif
   hash_entry_t* entry;
   #ifdef HTABLE_MAINTAIN_LIST
      entry = table->first;
      while (entry) {
         int r = _htable_bucket_insert(new_buckets, entry, new_hash_mask);
         #ifdef HTABLE_KEEP_STATS
         table->used_buckets += r;
         #endif
         entry = entry->next;
      }
   #else
      hash_entry_t* next;
      for (uint32_t i=0; i < table->bucket_count; i++) {
         entry = table->buckets[i];
         while (entry) {
            next = entry->bucket_next;
            int r = _htable_bucket_insert(new_buckets, entry, new_hash_mask);
            #ifdef HTABLE_KEEP_STATS
            table->used_buckets += r;
            #endif
            entry = next;
         }
      }
   #endif
   free(table->buckets);
   table->buckets = new_buckets;
   table->bucket_count = new_bucket_count;
   table->hash_mask = new_hash_mask;
}


// Get the pointer to the value of the entry or NULL if not in table
static YOUR_VALUE_T* htable_value(const hash_table_t* table, const char* key, size_t key_len) {
   // un-const table so that find_entry can keep statistics
   hash_entry_t* entry = htable_find_entry((hash_table_t*)table, key, key_len, NULL, NULL);
   return (entry != NULL) ? &entry->value : NULL;
}

static YOUR_VALUE_T htable_get(const hash_table_t* table, const char* key, size_t key_len, const YOUR_VALUE_T default_value) {
   // un-const table so that find_entry can keep statistics
   hash_entry_t* entry = htable_find_entry((hash_table_t*)table, key, key_len, NULL, NULL);
   return (entry != NULL) ? entry->value : default_value;
}

static int htable_exists(const hash_table_t* table, const char* key, size_t key_len) {
   // un-const table so that find_entry can keep statistics
   return (htable_find_entry((hash_table_t*)table, key, key_len, NULL, NULL) != NULL);
}

// Add a new entry (but don't update if it already exists)
// Returns NULL if the entry already exists (use set() if you want add or update logic)
static hash_entry_t* htable_add(hash_table_t* table, const char* key, size_t key_len, YOUR_VALUE_T value) {
   uint32_t hash;
   hash_entry_t* res = htable_find_entry(table, key, key_len, &hash, &key_len);
   if (res != NULL)
      return NULL;
   if ((res = (hash_entry_t*)malloc(sizeof(hash_entry_t))) == NULL)
      return NULL;
   if ((res->key = (char*)malloc(key_len + 1)) == NULL) {
      free(res);
      return NULL;
   }
   memcpy(res->key, key, key_len + 1);
   res->key_len = key_len;
   res->hash = hash;
   res->value = value;
   #ifdef HTABLE_MAINTAIN_LIST
   res->prev = NULL;
   res->next = NULL;
   if (table->first == NULL) {
      table->first = res;
      table->last = res;
   } else {
      res->prev = table->last;
      table->last->next = res;
      table->last = res;
   }
   #endif
   int r = _htable_bucket_insert(table->buckets, res, table->hash_mask);
   #ifdef HTABLE_KEEP_STATS
      table->used_buckets += r;
   #endif
   table->entry_count++;
   _htable_adjust_as_needed(table);
   return res;
}


static hash_entry_t* htable_set(hash_table_t* table, const char* key, size_t key_len, YOUR_VALUE_T value) {
   uint32_t hash;
   hash_entry_t* res = htable_find_entry(table, key, key_len, &hash, &key_len);
   if (res != NULL) {
      res->value = value;
      return res;
   }
   if ((res = (hash_entry_t*)malloc(sizeof(hash_entry_t))) == NULL)
      return NULL;
   if ((res->key = (char*)malloc(key_len + 1)) == NULL) {
      free(res);
      return NULL;
   }
   memcpy(res->key, key, key_len + 1);
   res->key_len = key_len;
   res->hash = hash;
   res->value = value;
   #ifdef HTABLE_MAINTAIN_LIST
   res->prev = NULL;
   res->next = NULL;
   if (table->first == NULL) {
      table->first = res;
      table->last = res;
   } else {
      res->prev = table->last;
      table->last->next = res;
      table->last = res;
   }
   #endif
   int r = _htable_bucket_insert(table->buckets, res, table->hash_mask);
   #ifdef HTABLE_KEEP_STATS
      table->used_buckets += r;
   #endif
   table->entry_count++;
   _htable_adjust_as_needed(table);
   return res;
}

// Update an entry but don't add a a new entry it doesn't already exist. Returns NULL if doesn't exist
static hash_entry_t* htable_update(hash_table_t* table, const char* key, size_t key_len, YOUR_VALUE_T value) {
   hash_entry_t* res = htable_find_entry(table, key, key_len, NULL, NULL);
   if (res == NULL)
      return NULL;
   res->value = value;
   return res;
}

// Delete an entry. Returns 1 on success or 0 if the entry didn't exist
static int htable_delete(hash_table_t* table, const char* key, size_t key_len) {
   uint32_t hash;
   hash_entry_t* entry = htable_find_entry(table, key, key_len, &hash, &key_len);
   if (entry == NULL)
      return 0;

   #ifdef HTABLE_MAINTAIN_LIST
      if (entry == table->first)
         table->first = entry->next;
      if (entry == table->last) {
         table->last = entry->prev;
      }
      if (entry->prev != NULL)
         entry->prev->next = entry->next;
      if (entry->next != NULL)
         entry->next->prev = entry->prev;
   #endif

   uint32_t bucket = hash & table->hash_mask;
   hash_entry_t* bhead = table->buckets[bucket];
   hash_entry_t* bprev = NULL;
   #ifdef HTABLE_FAST_DELETES
      bprev = entry->bucket_prev;
   #else
      if (bhead != entry) {
         bprev = bhead;
         while (bprev->bucket_next != entry)
            bprev = bprev->bucket_next;
      }
   #endif
   if (bprev != NULL)
      bprev->bucket_next = entry->bucket_next;

   #ifdef HTABLE_FAST_DELETES
      if (entry->bucket_next != NULL)
         entry->bucket_next->bucket_prev = entry->bucket_next;
   #endif

   if (bhead == entry) {
      table->buckets[bucket] = entry->bucket_next;
      #ifdef HTABLE_KEEP_STATS
         if (entry->bucket_next == NULL)
            table->used_buckets--;
      #endif
   }

   free(entry->key);
   free(entry);
   table->entry_count--;

   #ifndef HTABLE_FAST_DELETES
      htable_pack(table);
   #endif
   return 1;
}

static void htable_pack(hash_table_t* table) {
   _htable_adjust_as_needed(table);
}

此外，我还使用100000个随机生成的ASCII键（长度在5到1000个字符之间）进行了一些测试，结果如下所示

• 使用默认参数进行随机输入后：
  • 参赛人数：10万
  • 电话：131072
  • 二手桶：69790
  • 电话：30210
  • 错过：71394
  • 哈希/桶效率：69.79%
• 使用1/2的增长率进行随机输入后：
  • 参赛人数：10万
  • 电话：262144
  • 二手桶：83181
  • 电话：16819
  • 错过：35436
  • 哈希/桶效率：83.18%
• 使用2/1的增长率进行随机输入后：
  • 参赛人数：10万
  • 电话：65536
  • 二手桶：51368
  • 电话：48632
  • 失踪人数：141607
  • 哈希/桶效率：51.37%

正如你所看到的，它有潜力表现得相当好。80%的效率意味着约80%的查找为O（1），约16%的查找为O（2），约3.2%的查找为O（3），约0.8%的查找为O（4+）。这意味着平均一次查找需要O（1.248）

同样，50%的效率意味着50%的查找是O（1），25%是O（2），12.5%是O（3），12.5%是O（4+）

你真的只需要为你的已知因子选择（或编写）正确的散列算法，并根据你的具体需要调整

注:

这些断言/测试对我来说很有效，但不能保证没有bug。它看起来确实很稳定。可能有一两只虫子在里面漂浮

如果需要列表管理，您可以通过管理

entry->prev

和

entry->next

轻松添加

move（）

、

swap（）

、

sort（）

、

insert（）

等内容

我无法包含测试代码，因为我似乎已经达到了答案大小的限制

时间分析中不包括哈希函数或最终字符串比较。如果不了解有关输入的所有统计信息，就不可能对其进行分析。不过，这两个函数都应该非常快，如果知道有关输入数据的更多信息，则可以完全排除字符串比较

试试GPL'd，或者

程序：

• 接收查询字符串并通过枚举键列表来识别完美哈希函数的域

• 将这些键和列表大小（范围为1..size）提供给从上述参考实现派生的完美哈希生成函数

• 使用生成的完美哈希函数创建哈希映射

• 使用相同的完美哈希函数来处理HashMap中的

  get

  请求

编辑Necro

hash_table_t* ht = htable_create(0, 0, 0);
assert(ht != NULL);  // Table was created successfully

// Testing basic adding/updating/getting...
assert(htable_add(ht, "hello-world", 0, 234) != NULL); // hello-world set to 234
assert(htable_add(ht, "goodbye-world", 0, 567) != NULL); // goobye-world set to 567
assert(ht->entry_count == 2); // Two entries exist (hello-world and goodbye-world)
assert(htable_exists(ht, "hello-world", 0) == 1); // hello-world exists
assert(htable_exists(ht, "goodbye-world", 0) == 1); // goodbye-world exists
assert(htable_exists(ht, "unknown-world", 0) == 0); // unknown-world doesn't exist
assert(*htable_value(ht, "hello-world", 0) == 234); // hello-world has a value of 234
assert(*htable_value(ht, "goodbye-world", 0) == 567); // goodbye-world has a value of 567
assert(htable_get(ht, "hello-world", 0, -1) == 234); // hello-world exists and has a value of 234
assert(htable_get(ht, "goodbye-world", 0, -1) == 567); // goobye-world exists and has a value of 567
assert(htable_get(ht, "unknown-world", 0, -1) == -1); // unknown-world does not exist so the default value of -1 is returned
*htable_value(ht, "hello-world", 0) = -1; // hello-world's value is directly set via reference to -1
*htable_value(ht, "goodbye-world", 0) = -2; // goodbye-world's value is directly set via reference to -2
assert(*htable_value(ht, "hello-world", 0) == -1); // hello-world has a value of -1
assert(*htable_value(ht, "goodbye-world", 0) == -2); // goodbye-world has a value of -2
assert(htable_update(ht, "hello-world", 0, 1000) != NULL); // hello-world set to 1000
assert(htable_update(ht, "goodbye-world", 0, 2000) != NULL); // goodbye-world set to 2000
assert(htable_update(ht, "unknown-world", 0, 3000) == NULL); // unknown-world not set (it doesn't exist);
assert(ht->entry_count == 2); // Two entries exist (hello-world and goodbye-world)
assert(htable_set(ht, "hello-world", 0, 1111) != NULL); // hello-world set to 1111
assert(htable_set(ht, "goodbye-world", 0, 2222) != NULL); // goodbye-world set to 2222
assert(htable_set(ht, "unknown-world", 0, 3333) != NULL); // unknown-world added with a value of 3333
assert(ht->entry_count == 3); // Three entries exist (hello-world, goodbye-world, and unknown-world)
printf("%s\n", "After all additions and changes:");
#ifdef HTABLE_MAINTAIN_LIST
// A foreach iteration
hash_entry_t* entry = ht->first;
while (entry != NULL) {
   printf("\"%s\" = %i\n", entry->key, entry->value);
   entry = entry->next;
}
#endif
#ifdef HTABLE_KEEP_STATS
assert(ht->entry_count - ht->used_buckets == 0); // Means that no hash collisions occured
assert(ht->misses == 0); // Means that each lookup was in O(1) time
#endif

// Testing basic deletion...
assert(htable_delete(ht, "not-a-world", 0) == 0); // not-a-world not deleted (doesn't exist)
assert(htable_delete(ht, "hello-world", 0) == 1); // hello-world deleted
assert(htable_delete(ht, "hello-world", 0) == 0); // hello-world not deleted (doesn't exist)
assert(htable_exists(ht, "hello-world", 0) == 0); // hello-world doesn't exit
assert(htable_exists(ht, "goodbye-world", 0) == 1); // goobye-world still exists
assert(htable_exists(ht, "unknown-world", 0) == 1); // unknown-world still exists
assert(ht->entry_count == 2); // Two entries exists (goodbye-world and unknown-world)
assert(htable_delete(ht, "unknown-world", 0) == 1); // unknown-world deleted
assert(htable_exists(ht, "unknown-world", 0) == 0); // unknown-world doesn't exit
assert(htable_exists(ht, "goodbye-world", 0) == 1); // goodbye-world still exists
assert(ht->entry_count == 1); // One entry exists (goodbye-world)
#ifdef HTABLE_MAINTAIN_LIST
// A foreach iteration
printf("%s\n", "After deletion:");
entry = ht->first;
while (entry != NULL) {
   printf("\"%s\" = %i\n", entry->key, entry->value);
   entry = entry->next;
}
#endif

#ifdef HTABLE_KEEP_STATS
assert(ht->entry_count - ht->used_buckets == 0); // Means that no hash collisions occured
assert(ht->misses == 0); // Means that each lookup was in O(1) time
#endif

htable_free(ht);

get(field, table) 
{
   return table[perfect(field)];
}

Start with a number that is a prime (all primes are relative primes)
while (more bytes to be considered) {
  take the next byte of input and multiply it by a second prime
  determine the number of bits that might be lost in a left shift, capture them in a buffer
  shift the bits in the hash "buffer" to the left.
  restore the high order bit(s) in the low position
  take the next byte of input and multiply it by a second prime
  mask the multiplied result into the buffer 
}