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/* vi:set ts=8 sts=4 sw=4 noet:
*
* VIM - Vi IMproved by Bram Moolenaar
*
* Do ":help uganda" in Vim to read copying and usage conditions.
* Do ":help credits" in Vim to see a list of people who contributed.
* See README.txt for an overview of the Vim source code.
*/
/*
* hashtab.c: Handling of a hashtable with Vim-specific properties.
*
* Each item in a hashtable has a NUL terminated string key. A key can appear
* only once in the table.
*
* A hash number is computed from the key for quick lookup. When the hashes
* of two different keys point to the same entry an algorithm is used to
* iterate over other entries in the table until the right one is found.
* To make the iteration work removed keys are different from entries where a
* key was never present.
*
* The mechanism has been partly based on how Python Dictionaries are
* implemented. The algorithm is from Knuth Vol. 3, Sec. 6.4.
*
* The hashtable grows to accommodate more entries when needed. At least 1/3
* of the entries is empty to keep the lookup efficient (at the cost of extra
* memory).
*/
#include "vim.h"
#if 0
# define HT_DEBUG /* extra checks for table consistency and statistics */
static long hash_count_lookup = 0; /* count number of hashtab lookups */
static long hash_count_perturb = 0; /* count number of "misses" */
#endif
/* Magic value for algorithm that walks through the array. */
#define PERTURB_SHIFT 5
static int hash_may_resize(hashtab_T *ht, int minitems);
#if 0 /* currently not used */
/*
* Create an empty hash table.
* Returns NULL when out of memory.
*/
hashtab_T *
hash_create(void)
{
hashtab_T *ht;
ht = (hashtab_T *)alloc(sizeof(hashtab_T));
if (ht != NULL)
hash_init(ht);
return ht;
}
#endif
/*
* Initialize an empty hash table.
*/
void
hash_init(hashtab_T *ht)
{
/* This zeroes all "ht_" entries and all the "hi_key" in "ht_smallarray". */
vim_memset(ht, 0, sizeof(hashtab_T));
ht->ht_array = ht->ht_smallarray;
ht->ht_mask = HT_INIT_SIZE - 1;
}
#if defined(FEAT_EVAL) || defined(FEAT_SYN_HL) || defined(PROTO)
/*
* Free the array of a hash table. Does not free the items it contains!
* If "ht" is not freed then you should call hash_init() next!
*/
void
hash_clear(hashtab_T *ht)
{
if (ht->ht_array != ht->ht_smallarray)
vim_free(ht->ht_array);
}
/*
* Free the array of a hash table and all the keys it contains. The keys must
* have been allocated. "off" is the offset from the start of the allocate
* memory to the location of the key (it's always positive).
*/
void
hash_clear_all(hashtab_T *ht, int off)
{
long todo;
hashitem_T *hi;
todo = (long)ht->ht_used;
for (hi = ht->ht_array; todo > 0; ++hi)
{
if (!HASHITEM_EMPTY(hi))
{
vim_free(hi->hi_key - off);
--todo;
}
}
hash_clear(ht);
}
#endif
/*
* Find "key" in hashtable "ht". "key" must not be NULL.
* Always returns a pointer to a hashitem. If the item was not found then
* HASHITEM_EMPTY() is TRUE. The pointer is then the place where the key
* would be added.
* WARNING: The returned pointer becomes invalid when the hashtable is changed
* (adding, setting or removing an item)!
*/
hashitem_T *
hash_find(hashtab_T *ht, char_u *key)
{
return hash_lookup(ht, key, hash_hash(key));
}
/*
* Like hash_find(), but caller computes "hash".
*/
hashitem_T *
hash_lookup(hashtab_T *ht, char_u *key, hash_T hash)
{
hash_T perturb;
hashitem_T *freeitem;
hashitem_T *hi;
unsigned idx;
#ifdef HT_DEBUG
++hash_count_lookup;
#endif
/*
* Quickly handle the most common situations:
* - return if there is no item at all
* - skip over a removed item
* - return if the item matches
*/
idx = (unsigned)(hash & ht->ht_mask);
hi = &ht->ht_array[idx];
if (hi->hi_key == NULL)
return hi;
if (hi->hi_key == HI_KEY_REMOVED)
freeitem = hi;
else if (hi->hi_hash == hash && STRCMP(hi->hi_key, key) == 0)
return hi;
else
freeitem = NULL;
/*
* Need to search through the table to find the key. The algorithm
* to step through the table starts with large steps, gradually becoming
* smaller down to (1/4 table size + 1). This means it goes through all
* table entries in the end.
* When we run into a NULL key it's clear that the key isn't there.
* Return the first available slot found (can be a slot of a removed
* item).
*/
for (perturb = hash; ; perturb >>= PERTURB_SHIFT)
{
#ifdef HT_DEBUG
++hash_count_perturb; /* count a "miss" for hashtab lookup */
#endif
idx = (unsigned)((idx << 2U) + idx + perturb + 1U);
hi = &ht->ht_array[idx & ht->ht_mask];
if (hi->hi_key == NULL)
return freeitem == NULL ? hi : freeitem;
if (hi->hi_hash == hash
&& hi->hi_key != HI_KEY_REMOVED
&& STRCMP(hi->hi_key, key) == 0)
return hi;
if (hi->hi_key == HI_KEY_REMOVED && freeitem == NULL)
freeitem = hi;
}
}
/*
* Print the efficiency of hashtable lookups.
* Useful when trying different hash algorithms.
* Called when exiting.
*/
void
hash_debug_results(void)
{
#ifdef HT_DEBUG
fprintf(stderr, "\r\n\r\n\r\n\r\n");
fprintf(stderr, "Number of hashtable lookups: %ld\r\n", hash_count_lookup);
fprintf(stderr, "Number of perturb loops: %ld\r\n", hash_count_perturb);
fprintf(stderr, "Percentage of perturb loops: %ld%%\r\n",
hash_count_perturb * 100 / hash_count_lookup);
#endif
}
/*
* Add item with key "key" to hashtable "ht".
* Returns FAIL when out of memory or the key is already present.
*/
int
hash_add(hashtab_T *ht, char_u *key)
{
hash_T hash = hash_hash(key);
hashitem_T *hi;
hi = hash_lookup(ht, key, hash);
if (!HASHITEM_EMPTY(hi))
{
internal_error("hash_add()");
return FAIL;
}
return hash_add_item(ht, hi, key, hash);
}
/*
* Add item "hi" with "key" to hashtable "ht". "key" must not be NULL and
* "hi" must have been obtained with hash_lookup() and point to an empty item.
* "hi" is invalid after this!
* Returns OK or FAIL (out of memory).
*/
int
hash_add_item(
hashtab_T *ht,
hashitem_T *hi,
char_u *key,
hash_T hash)
{
/* If resizing failed before and it fails again we can't add an item. */
if (ht->ht_error && hash_may_resize(ht, 0) == FAIL)
return FAIL;
++ht->ht_used;
if (hi->hi_key == NULL)
++ht->ht_filled;
hi->hi_key = key;
hi->hi_hash = hash;
/* When the space gets low may resize the array. */
return hash_may_resize(ht, 0);
}
#if 0 /* not used */
/*
* Overwrite hashtable item "hi" with "key". "hi" must point to the item that
* is to be overwritten. Thus the number of items in the hashtable doesn't
* change.
* Although the key must be identical, the pointer may be different, thus it's
* set anyway (the key is part of an item with that key).
* The caller must take care of freeing the old item.
* "hi" is invalid after this!
*/
void
hash_set(hashitem_T *hi, char_u *key)
{
hi->hi_key = key;
}
#endif
/*
* Remove item "hi" from hashtable "ht". "hi" must have been obtained with
* hash_lookup().
* The caller must take care of freeing the item itself.
*/
void
hash_remove(hashtab_T *ht, hashitem_T *hi)
{
--ht->ht_used;
hi->hi_key = HI_KEY_REMOVED;
hash_may_resize(ht, 0);
}
/*
* Lock a hashtable: prevent that ht_array changes.
* Don't use this when items are to be added!
* Must call hash_unlock() later.
*/
void
hash_lock(hashtab_T *ht)
{
++ht->ht_locked;
}
#if 0 /* currently not used */
/*
* Lock a hashtable at the specified number of entries.
* Caller must make sure no more than "size" entries will be added.
* Must call hash_unlock() later.
*/
void
hash_lock_size(hashtab_T *ht, int size)
{
(void)hash_may_resize(ht, size);
++ht->ht_locked;
}
#endif
/*
* Unlock a hashtable: allow ht_array changes again.
* Table will be resized (shrink) when necessary.
* This must balance a call to hash_lock().
*/
void
hash_unlock(hashtab_T *ht)
{
--ht->ht_locked;
(void)hash_may_resize(ht, 0);
}
/*
* Shrink a hashtable when there is too much empty space.
* Grow a hashtable when there is not enough empty space.
* Returns OK or FAIL (out of memory).
*/
static int
hash_may_resize(
hashtab_T *ht,
int minitems) /* minimal number of items */
{
hashitem_T temparray[HT_INIT_SIZE];
hashitem_T *oldarray, *newarray;
hashitem_T *olditem, *newitem;
unsigned newi;
int todo;
long_u oldsize, newsize;
long_u minsize;
long_u newmask;
hash_T perturb;
/* Don't resize a locked table. */
if (ht->ht_locked > 0)
return OK;
#ifdef HT_DEBUG
if (ht->ht_used > ht->ht_filled)
EMSG("hash_may_resize(): more used than filled");
if (ht->ht_filled >= ht->ht_mask + 1)
EMSG("hash_may_resize(): table completely filled");
#endif
if (minitems == 0)
{
/* Return quickly for small tables with at least two NULL items. NULL
* items are required for the lookup to decide a key isn't there. */
if (ht->ht_filled < HT_INIT_SIZE - 1
&& ht->ht_array == ht->ht_smallarray)
return OK;
/*
* Grow or refill the array when it's more than 2/3 full (including
* removed items, so that they get cleaned up).
* Shrink the array when it's less than 1/5 full. When growing it is
* at least 1/4 full (avoids repeated grow-shrink operations)
*/
oldsize = ht->ht_mask + 1;
if (ht->ht_filled * 3 < oldsize * 2 && ht->ht_used > oldsize / 5)
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