学习twitter的高性能散列表源码：
个人认为Twitter散列表的优点：
1、使用C宏定义实现C++泛型的思想；
2、散列函数冲突小；
3、使用bitmap思想，标志位占用空间小；
4、自动扩展容量，判断扩容的条件；
个人认为Twitter散列表的缺点：
1、值的类型都用指针指向，对于值类型是简单整型有指针占用空间的缺点；（虽然值类型是基本整型的情况较少，但是可以通过宏进行值类型是基本类型进行选定）
1、使用C的#define写类似于C++泛型的代码；
#define KHASH_INIT2(name, SCOPE, khkey_t, khval_t, kh_is_map, __hash_func, __hash_equal) \
__KHASH_TYPE(name, khkey_t, khval_t) \
__KHASH_IMPL(name, SCOPE, khkey_t, khval_t, kh_is_map, __hash_func, __hash_equal)
name:散列表的名称可以自定义；
khval_t：散列表的值类型可以自定义，在散列表里是指针；
khkey_t：散列表的key可以不可以自定义，但是可以选择32位或者64位的key；
__hash_func：散列函数可以选择，提供很多种散列函数；
/* --- BEGIN OF HASH FUNCTIONS --- */
/*! @function
@abstract Integer hash function
@param key The integer [khint32_t]
@return The hash value [khint_t]
*/
#define kh_int_hash_func(key) (khint32_t)(key)
/*! @function
@abstract Integer comparison function
*/
#define kh_int_hash_equal(a, b) ((a) == (b))
/*! @function
@abstract 64-bit integer hash function
@param key The integer [khint64_t]
@return The hash value [khint_t]
*/
#define kh_int64_hash_func(key) (khint32_t)((key)>>33^(key)^(key)<<11)
/*! @function
@abstract 64-bit integer comparison function
*/
#define kh_int64_hash_equal(a, b) ((a) == (b))
/*! @function
@abstract const char* hash function
@param s Pointer to a null terminated string
@return The hash value
*/
static kh_inline khint_t __ac_X31_hash_string(const char *s)
{
khint_t h = (khint_t)*s;
if (h) for (++s ; *s; ++s) h = (h << 5) - h + (khint_t)*s;
return h;
}
/*! @function
@abstract Another interface to const char* hash function
@param key Pointer to a null terminated string [const char*]
@return The hash value [khint_t]
*/
#define kh_str_hash_func(key) __ac_X31_hash_string(key)
/*! @function
@abstract Const char* comparison function
*/
#define kh_str_hash_equal(a, b) (strcmp(a, b) == 0)
static kh_inline khint_t __ac_Wang_hash(khint_t key)
{
key += ~(key << 15);
key ^= (key >> 10);
key += (key << 3);
key ^= (key >> 6);
key += ~(key << 11);
key ^= (key >> 16);
return key;
}
#define kh_int_hash_func2(key) __ac_Wang_hash((khint_t)key)
__hash_equal：散列里面的判断key相等，因为只有32和64的整数，所以不可以选择；
下面的定义类型结构体：
__KHASH_TYPE(name, khkey_t, khval_t)
#define __KHASH_TYPE(name, khkey_t, khval_t) \
typedef struct kh_##name##_s {
\
khint_t n_buckets, size, n_occupied, upper_bound; \
khint32_t *flags; \
khkey_t *keys; \
khval_t *vals; \
} kh_##name##_t;
下面的定义name和khval_t的函数：
__KHASH_IMPL(name, SCOPE, khkey_t, khval_t, kh_is_map, __hash_func, __hash_equal)
#define __KHASH_IMPL(name, SCOPE, khkey_t, khval_t, kh_is_map, __hash_func, __hash_equal) \
SCOPE kh_##name##_t *kh_init_##name(void) {
\
return (kh_##name##_t*)kcalloc(1, sizeof(kh_##name##_t)); \
} \
SCOPE void kh_destroy_##name(kh_##name##_t *h) \
{
\
if (h) {
\
kfree((void *)h->keys); kfree(h->flags); \
kfree((void *)h->vals); \
kfree(h); \
} \
} \
SCOPE void kh_clear_##name(kh_##name##_t *h) \
{
\
if (h && h->flags) {
\
memset(h->flags, 0xaa, __ac_fsize(h->n_buckets) * sizeof(khint32_t)); \
h->size = h->n_occupied = 0; \
} \
} \
SCOPE khint_t kh_get_##name(const kh_##name##_t *h, khkey_t key) \
{
\
if (h->n_buckets) {
\
khint_t k, i, last, mask, step = 0; \
mask = h->n_buckets - 1; \
k = __hash_func(key); i = k & mask; \
last = i; \
while (!__ac_isempty(h->flags, i) && (__ac_isdel(h->flags, i) || !__hash_equal(h->keys[i], key))) {
\
i = (i + (++step)) & mask; \
if (i == last) return h->n_buckets; \
} \
return __ac_iseither(h->flags, i)? h->n_buckets : i; \
} else return 0; \
} \
SCOPE int kh_resize_##name(kh_##name##_t *h, khint_t new_n_buckets) \
{
/* This function uses 0.25*n_buckets bytes of working space instead of [sizeof(key_t+val_t)+.25]*n_buckets. */ \
khint32_t *new_flags = 0; \
khint_t j = 1; \
{
\
kroundup32(new_n_buckets); \
if (new_n_buckets < 4) new_n_buckets = 4; \
if (h->size >= (khint_t)(new_n_buckets * __ac_HASH_UPPER + 0.5)) j = 0; /* requested size is too small */ \
else {
/* hash table size to be changed (shrink or expand); rehash */ \
new_flags = (khint32_t*)kmalloc(__ac_fsize(new_n_buckets) * sizeof(khint32_t)); \
if (!new_flags) return -1; \
memset(new_flags, 0xaa, __ac_fsize(new_n_buckets) * sizeof(khint32_t)); \
if (h->n_buckets < new_n_buckets) {
/* expand */ \
khkey_t *new_keys = (khkey_t*)krealloc((void *)h->keys, new_n_buckets * sizeof(khkey_t)); \
if (!new_keys) {
kfree(new_flags); return -1; } \
h->keys = new_keys; \
if (kh_is_map) {
\
khval_t *new_vals = (khval_t*)krealloc((void *)h->vals, new_n_buckets * sizeof(khval_t)); \
if (!new_vals) {
kfree(new_flags); return -1; } \
h->vals = new_vals; \
} \
} /* otherwise shrink */ \
} \
} \
if (j) {
/* rehashing is needed */ \
for (j = 0; j != h->n_buckets; ++j) {
\
if (__ac_iseither(h->flags, j) == 0) {
\
khkey_t key = h->keys[j]; \
khval_t val; \
khint_t new_mask; \
new_mask = new_n_buckets - 1; \
if (kh_is_map) val = h->vals[j]; \
__ac_set_isdel_true(h->flags, j); \
while (1) {
/* kick-out process; sort of like in Cuckoo hashing */ \
khint_t k, i, step = 0; \
k = __hash_func(key); \
i = k & new_mask; \
while (!__ac_isempty(new_flags, i)) i = (i + (++step)) & new_mask; \
__ac_set_isempty_false(new_flags, i); \
if (i < h->n_buckets && __ac_iseither(h->flags, i) == 0) {
/* kick out the existing element */ \
{
khkey_t tmp = h->keys[i]; h->keys[i] = key; key = tmp; } \
if (kh_is_map) {
khval_t tmp = h->vals[i]; h->vals[i] = val; val = tmp; } \
__ac_set_isdel_true(h->flags, i); /* mark it as deleted in the old hash table */ \
} else {
/* write the element and jump out of the loop */ \
h->keys[i] = key; \
if (kh_is_map) h->vals[i] = val; \
break; \
} \
} \
} \
} \
if (h->n_buckets > new_n_buckets) {
/* shrink the hash table */ \
h->keys = (khkey_t*)krealloc((void *)h->keys, new_n_buckets * sizeof(khkey_t)); \
if (kh_is_map) h->vals = (khval_t*)krealloc((void *)h->vals, new_n_buckets * sizeof(khval_t)); \
} \
kfree(h->flags); /* free the working space */ \
h->flags = new_flags; \
h->n_buckets = new_n_buckets; \
h->n_occupied = h->size; \
h->upper_bound = (khint_t)(h->n_buckets * __ac_HASH_UPPER + 0.5); \
} \
return 0; \
} \
SCOPE khint_t kh_put_##name(kh_##name##_t *h, khkey_t key, int *ret) \
{
\
khint_t x; \
if (h->n_occupied >= h->upper_bound) {
/* update the hash table */ \
if (h->n_buckets > (h->size<<1)) {
\
if (kh_resize_##name(h, h->n_buckets - 1) < 0) {
/* clear "deleted" elements */ \
*ret = -1; return h->n_buckets; \
} \
} else if (kh_resize_##name(h, h->n_buckets + 1) < 0) {
/* expand the hash table */ \
*ret = -1; return h->n_buckets; \
} \
} /* TODO: to implement automatically shrinking; resize() already support shrinking */ \
{
\
khint_t k, i, site, last, mask = h->n_buckets - 1, step = 0; \
x = site = h->n_buckets; k = __hash_func(key); i = k & mask; \
if (__ac_isempty(h->flags, i)) x = i; /* for speed up */ \
else {
\
last = i; \
while (!__ac_isempty(h->flags, i) && (__ac_isdel(h->flags, i) || !__hash_equal(h->keys[i], key))) {
\
if (__ac_isdel(h->flags, i)) site = i; \
i = (i + (++step)) & mask; \
if (i == last) {
x = site; break; } \
} \
if (x == h->n_buckets) {
\
if (__ac_isempty(h->flags, i) && site != h->n_buckets) x = site; \
else x = i; \
} \
} \
} \
if (__ac_isempty(h->flags, x)) {
/* not present at all */ \
h->keys[x] = key; \
__ac_set_isboth_false(h->flags, x); \
++h->size; ++h->n_occupied; \
*ret = 1; \
} else if (__ac_isdel(h->flags, x)) {
/* deleted */ \
h->keys[x] = key; \
__ac_set_isboth_false(h->flags, x); \
++h->size; \
*ret = 2; \
} else *ret = 0; /* Don't touch h->keys[x] if present and not deleted */ \
return x; \
} \
SCOPE void kh_del_##name(kh_##name##_t *h, khint_t x) \
{
\
if (x != h->n_buckets && !__ac_iseither(h->flags, x)) {
\
__ac_set_isdel_true(h->flags, x); \
--h->size; \
} \
}
2、散列表支持动态扩展桶的数目；
在put函数里面，会判断，如果满足
h->n_occupied >= h->upper_bound
则通过resize进行扩展：
khint_t x;
if (h->n_occupied >= h->upper_bound) {
/* update the hash table */
if (h->n_buckets > (h->size<<1)) {
if (kh_resize_##name(h, h->n_buckets - 1) < 0) {
/* clear "deleted" elements */
*ret = -1; return h->n_buckets;
}
} else if (kh_resize_##name(h, h->n_buckets + 1) < 0) {
/* expand the hash table */
*ret = -1; return h->n_buckets;
}
}
3、使用bitmap作为桶有没有被放置的标记；
khint32_t *flags;//散列表里的bit标志，bitmap
加上一系列对于bitmap的快速位操作，进行判断空、某个位置是否存在key等
#define __ac_isempty(flag, i) ((flag[i>>4]>>((i&0xfU)<<1))&2)
#define __ac_isdel(flag, i) ((flag[i>>4]>>((i&0xfU)<<1))&1)
#define __ac_iseither(flag, i) ((flag[i>>4]>>((i&0xfU)<<1))&3)
#define __ac_set_isdel_false(flag, i) (flag[i>>4]&=~(1ul<<((i&0xfU)<<1)))
#define __ac_set_isempty_false(flag, i) (flag[i>>4]&=~(2ul<<((i&0xfU)<<1)))
#define __ac_set_isboth_false(flag, i) (flag[i>>4]&=~(3ul<<((i&0xfU)<<1)))
#define __ac_set_isdel_true(flag, i) (flag[i>>4]|=1ul<<((i&0xfU)<<1))
4、定义一些工具函数
//函数声明
#define __KHASH_PROTOTYPES(name, khkey_t, khval_t) \
extern kh_##name##_t *kh_init_##name(void); \
extern void kh_destroy_##name(kh_##name##_t *h); \
extern void kh_clear_##name(kh_##name##_t *h); \
extern khint_t kh_get_##name(const kh_##name##_t *h, khkey_t key); \
extern int kh_resize_##name(kh_##name##_t *h, khint_t new_n_buckets); \
extern khint_t kh_put_##name(kh_##name##_t *h, khkey_t key, int *ret); \
extern void kh_del_##name(kh_##name##_t *h, khint_t x);
//方便使用的宏定义，可以通过name和语义进行调用；
/*!
@abstract Type of the hash table.
@param name Name of the hash table [symbol]
*/
#define khash_t(name) kh_##name##_t
/*! @function
@abstract Initiate a hash table.
@param name Name of the hash table [symbol]
@return Pointer to the hash table [khash_t(name)*]
*/
#define kh_init(name) kh_init_##name()
/*! @function
@abstract Destroy a hash table.
@param name Name of the hash table [symbol]
@param h Pointer to the hash table [khash_t(name)*]
*/
#define kh_destroy(name, h) kh_destroy_##name(h)
/*! @function
@abstract Reset a hash table without deallocating memory.
@param name Name of the hash table [symbol]
@param h Pointer to the hash table [khash_t(name)*]
*/
#define kh_clear(name, h) kh_clear_##name(h)
/*! @function
@abstract Resize a hash table.
@param name Name of the hash table [symbol]
@param h Pointer to the hash table [khash_t(name)*]
@param s New size [khint_t]
*/
#define kh_resize(name, h, s) kh_resize_##name(h, s)
/*! @function
@abstract Insert a key to the hash table.
@param name Name of the hash table [symbol]
@param h Pointer to the hash table [khash_t(name)*]
@param k Key [type of keys]
@param r Extra return code: -1 if the operation failed;
0 if the key is present in the hash table;
1 if the bucket is empty (never used); 2 if the element in
the bucket has been deleted [int*]
@return Iterator to the inserted element [khint_t]
*/
#define kh_put(name, h, k, r) kh_put_##name(h, k, r)
/*! @function
@abstract Retrieve a key from the hash table.
@param name Name of the hash table [symbol]
@param h Pointer to the hash table [khash_t(name)*]
@param k Key [type of keys]
@return Iterator to the found element, or kh_end(h) if the element is absent [khint_t]
*/
#define kh_get(name, h, k) kh_get_##name(h, k)
/*! @function
@abstract Remove a key from the hash table.
@param name Name of the hash table [symbol]
@param h Pointer to the hash table [khash_t(name)*]
@param k Iterator to the element to be deleted [khint_t]
*/
#define kh_del(name, h, k) kh_del_##name(h, k)
/*! @function
@abstract Test whether a bucket contains data.
@param h Pointer to the hash table [khash_t(name)*]
@param x Iterator to the bucket [khint_t]
@return 1 if containing data; 0 otherwise [int]
*/
#define kh_exist(h, x) (!__ac_iseither((h)->flags, (x)))
/*! @function
@abstract Get key given an iterator
@param h Pointer to the hash table [khash_t(name)*]
@param x Iterator to the bucket [khint_t]
@return Key [type of keys]
*/
#define kh_key(h, x) ((h)->keys[x])
/*! @function
@abstract Get value given an iterator
@param h Pointer to the hash table [khash_t(name)*]
@param x Iterator to the bucket [khint_t]
@return Value [type of values]
@discussion For hash sets, calling this results in segfault.
*/
#define kh_val(h, x) ((h)->vals[x])
/*! @function
@abstract Alias of kh_val()
*/
#define kh_value(h, x) ((h)->vals[x])
/*! @function
@abstract Get the start iterator
@param h Pointer to the hash table [khash_t(name)*]
@return The start iterator [khint_t]
*/
#define kh_begin(h) (khint_t)(0)
/*! @function
@abstract Get the end iterator
@param h Pointer to the hash table [khash_t(name)*]
@return The end iterator [khint_t]
*/
#define kh_end(h) ((h)->n_buckets)
/*! @function
@abstract Get the number of elements in the hash table
@param h Pointer to the hash table [khash_t(name)*]
@return Number of elements in the hash table [khint_t]
*/
#define kh_size(h) ((h)->size)
/*! @function
@abstract Get the number of buckets in the hash table
@param h Pointer to the hash table [khash_t(name)*]
@return Number of buckets in the hash table [khint_t]
*/
#define kh_n_buckets(h) ((h)->n_buckets)
/*! @function
@abstract Iterate over the entries in the hash table
@param h Pointer to the hash table [khash_t(name)*]
@param kvar Variable to which key will be assigned
@param vvar Variable to which value will be assigned
@param code Block of code to execute
*/
#define kh_foreach(h, kvar, vvar, code) {
khint_t __i; \
for (__i = kh_begin(h); __i != kh_end(h); ++__i) {
\
if (!kh_exist(h,__i)) continue; \
(kvar) = kh_key(h,__i); \
(vvar) = kh_val(h,__i); \
code; \
} }
/*! @function
@abstract Iterate over the values in the hash table
@param h Pointer to the hash table [khash_t(name)*]
@param vvar Variable to which value will be assigned
@param code Block of code to execute
*/
#define kh_foreach_value(h, vvar, code) {
khint_t __i; \
for (__i = kh_begin(h); __i != kh_end(h); ++__i) {
\
if (!kh_exist(h,__i)) continue; \
(vvar) = kh_val(h,__i); \
code; \
} }
/* More conenient interfaces */
/*! @function
@abstract Instantiate a hash set containing integer keys
@param name Name of the hash table [symbol]
*/
#define KHASH_SET_INIT_INT(name) \
KHASH_INIT(name, khint32_t, char, 0, kh_int_hash_func, kh_int_hash_equal)
/*! @function
@abstract Instantiate a hash map containing integer keys
@param name Name of the hash table [symbol]
@param khval_t Type of values [type]
*/
#define KHASH_MAP_INIT_INT(name, khval_t) \
KHASH_INIT(name, khint32_t, khval_t, 1, kh_int_hash_func, kh_int_hash_equal)
/*! @function
@abstract Instantiate a hash map containing 64-bit integer keys
@param name Name of the hash table [symbol]
*/
#define KHASH_SET_INIT_INT64(name) \
KHASH_INIT(name, khint64_t, char, 0, kh_int64_hash_func, kh_int64_hash_equal)
/*! @function
@abstract Instantiate a hash map containing 64-bit integer keys
@param name Name of the hash table [symbol]
@param khval_t Type of values [type]
*/
#define KHASH_MAP_INIT_INT64(name, khval_t) \
KHASH_INIT(name, khint64_t, khval_t, 1, kh_int64_hash_func, kh_int64_hash_equal)
typedef const char *kh_cstr_t;
/*! @function
@abstract Instantiate a hash map containing const char* keys
@param name Name of the hash table [symbol]
*/
#define KHASH_SET_INIT_STR(name) \
KHASH_INIT(name, kh_cstr_t, char, 0, kh_str_hash_func, kh_str_hash_equal)
/*! @function
@abstract Instantiate a hash map containing const char* keys
@param name Name of the hash table [symbol]
@param khval_t Type of values [type]
*/
#define KHASH_MAP_INIT_STR(name, khval_t) \
KHASH_INIT(name, kh_cstr_t, khval_t, 1, kh_str_hash_func, kh_str_hash_equal)
使用散列表
KHASH_MAP_INIT_INT(32, char)
void test_khash_map()
{
int ret, is_missing;
khiter_t k;
khash_t(32)* h = kh_init(32);
k = kh_put(32, h, 5, &ret);
kh_value(h, k) = 10;
k = kh_get(32, h, 10);
is_missing = (k == kh_end(h));
k = kh_get(32, h, 5);
kh_del(32, h, k);
for (k = kh_begin(h); k != kh_end(h); ++k)
if (kh_exist(h, k)) kh_value(h, k) = 1;
kh_destroy(32, h);
return;
}