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https://github.com/neovim/neovim.git
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Import vim from changeset v5628:c9cad40b4181
- Cleanup source tree, leaving only files necessary for compilation/testing - Process files through unifdef to remove tons of FEAT_* macros - Process files through uncrustify to normalize source code formatting. - Port the build system to cmake
This commit is contained in:
Thiago de Arruda
416
src/hashtab.c
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416
src/hashtab.c
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/* vi:set ts=8 sts=4 sw=4:
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*
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* VIM - Vi IMproved by Bram Moolenaar
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*
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* Do ":help uganda" in Vim to read copying and usage conditions.
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* Do ":help credits" in Vim to see a list of people who contributed.
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* See README.txt for an overview of the Vim source code.
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*/
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/*
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* hashtab.c: Handling of a hashtable with Vim-specific properties.
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*
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* Each item in a hashtable has a NUL terminated string key. A key can appear
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* only once in the table.
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*
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* A hash number is computed from the key for quick lookup. When the hashes
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* of two different keys point to the same entry an algorithm is used to
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* iterate over other entries in the table until the right one is found.
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* To make the iteration work removed keys are different from entries where a
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* key was never present.
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*
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* The mechanism has been partly based on how Python Dictionaries are
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* implemented. The algorithm is from Knuth Vol. 3, Sec. 6.4.
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*
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* The hashtable grows to accommodate more entries when needed. At least 1/3
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* of the entries is empty to keep the lookup efficient (at the cost of extra
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* memory).
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*/
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#include "vim.h"
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/* Magic value for algorithm that walks through the array. */
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#define PERTURB_SHIFT 5
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static int hash_may_resize __ARGS((hashtab_T *ht, int minitems));
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/*
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* Initialize an empty hash table.
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*/
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void hash_init(ht)
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hashtab_T *ht;
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{
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/* This zeroes all "ht_" entries and all the "hi_key" in "ht_smallarray". */
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vim_memset(ht, 0, sizeof(hashtab_T));
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ht->ht_array = ht->ht_smallarray;
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ht->ht_mask = HT_INIT_SIZE - 1;
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}
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/*
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* Free the array of a hash table. Does not free the items it contains!
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* If "ht" is not freed then you should call hash_init() next!
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*/
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void hash_clear(ht)
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hashtab_T *ht;
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{
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if (ht->ht_array != ht->ht_smallarray)
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vim_free(ht->ht_array);
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}
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/*
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* Free the array of a hash table and all the keys it contains. The keys must
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* have been allocated. "off" is the offset from the start of the allocate
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* memory to the location of the key (it's always positive).
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*/
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void hash_clear_all(ht, off)
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hashtab_T *ht;
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int off;
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{
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long todo;
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hashitem_T *hi;
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todo = (long)ht->ht_used;
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for (hi = ht->ht_array; todo > 0; ++hi) {
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if (!HASHITEM_EMPTY(hi)) {
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vim_free(hi->hi_key - off);
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--todo;
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}
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}
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hash_clear(ht);
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}
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/*
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* Find "key" in hashtable "ht". "key" must not be NULL.
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* Always returns a pointer to a hashitem. If the item was not found then
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* HASHITEM_EMPTY() is TRUE. The pointer is then the place where the key
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* would be added.
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* WARNING: The returned pointer becomes invalid when the hashtable is changed
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* (adding, setting or removing an item)!
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*/
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hashitem_T * hash_find(ht, key)
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hashtab_T *ht;
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char_u *key;
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{
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return hash_lookup(ht, key, hash_hash(key));
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}
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/*
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* Like hash_find(), but caller computes "hash".
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*/
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hashitem_T * hash_lookup(ht, key, hash)
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hashtab_T *ht;
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char_u *key;
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hash_T hash;
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{
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hash_T perturb;
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hashitem_T *freeitem;
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hashitem_T *hi;
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unsigned idx;
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#ifdef HT_DEBUG
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++hash_count_lookup;
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#endif
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/*
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* Quickly handle the most common situations:
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* - return if there is no item at all
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* - skip over a removed item
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* - return if the item matches
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*/
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idx = (unsigned)(hash & ht->ht_mask);
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hi = &ht->ht_array[idx];
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if (hi->hi_key == NULL)
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return hi;
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if (hi->hi_key == HI_KEY_REMOVED)
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freeitem = hi;
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else if (hi->hi_hash == hash && STRCMP(hi->hi_key, key) == 0)
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return hi;
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else
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freeitem = NULL;
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/*
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* Need to search through the table to find the key. The algorithm
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* to step through the table starts with large steps, gradually becoming
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* smaller down to (1/4 table size + 1). This means it goes through all
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* table entries in the end.
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* When we run into a NULL key it's clear that the key isn't there.
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* Return the first available slot found (can be a slot of a removed
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* item).
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*/
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for (perturb = hash;; perturb >>= PERTURB_SHIFT) {
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#ifdef HT_DEBUG
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++hash_count_perturb; /* count a "miss" for hashtab lookup */
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#endif
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idx = (unsigned)((idx << 2U) + idx + perturb + 1U);
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hi = &ht->ht_array[idx & ht->ht_mask];
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if (hi->hi_key == NULL)
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return freeitem == NULL ? hi : freeitem;
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if (hi->hi_hash == hash
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&& hi->hi_key != HI_KEY_REMOVED
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&& STRCMP(hi->hi_key, key) == 0)
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return hi;
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if (hi->hi_key == HI_KEY_REMOVED && freeitem == NULL)
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freeitem = hi;
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}
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}
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/*
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* Print the efficiency of hashtable lookups.
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* Useful when trying different hash algorithms.
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* Called when exiting.
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*/
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void hash_debug_results() {
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#ifdef HT_DEBUG
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fprintf(stderr, "\r\n\r\n\r\n\r\n");
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fprintf(stderr, "Number of hashtable lookups: %ld\r\n", hash_count_lookup);
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fprintf(stderr, "Number of perturb loops: %ld\r\n", hash_count_perturb);
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fprintf(stderr, "Percentage of perturb loops: %ld%%\r\n",
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hash_count_perturb * 100 / hash_count_lookup);
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#endif
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}
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/*
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* Add item with key "key" to hashtable "ht".
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* Returns FAIL when out of memory or the key is already present.
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*/
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int hash_add(ht, key)
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hashtab_T *ht;
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char_u *key;
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{
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hash_T hash = hash_hash(key);
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hashitem_T *hi;
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hi = hash_lookup(ht, key, hash);
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if (!HASHITEM_EMPTY(hi)) {
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EMSG2(_(e_intern2), "hash_add()");
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return FAIL;
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}
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return hash_add_item(ht, hi, key, hash);
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}
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/*
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* Add item "hi" with "key" to hashtable "ht". "key" must not be NULL and
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* "hi" must have been obtained with hash_lookup() and point to an empty item.
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* "hi" is invalid after this!
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* Returns OK or FAIL (out of memory).
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*/
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int hash_add_item(ht, hi, key, hash)
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hashtab_T *ht;
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hashitem_T *hi;
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char_u *key;
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hash_T hash;
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{
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/* If resizing failed before and it fails again we can't add an item. */
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if (ht->ht_error && hash_may_resize(ht, 0) == FAIL)
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return FAIL;
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++ht->ht_used;
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if (hi->hi_key == NULL)
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++ht->ht_filled;
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hi->hi_key = key;
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hi->hi_hash = hash;
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/* When the space gets low may resize the array. */
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return hash_may_resize(ht, 0);
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}
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/*
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* Remove item "hi" from hashtable "ht". "hi" must have been obtained with
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* hash_lookup().
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* The caller must take care of freeing the item itself.
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*/
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void hash_remove(ht, hi)
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hashtab_T *ht;
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hashitem_T *hi;
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{
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--ht->ht_used;
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hi->hi_key = HI_KEY_REMOVED;
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hash_may_resize(ht, 0);
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}
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/*
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* Lock a hashtable: prevent that ht_array changes.
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* Don't use this when items are to be added!
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* Must call hash_unlock() later.
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*/
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void hash_lock(ht)
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hashtab_T *ht;
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{
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++ht->ht_locked;
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}
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/*
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* Unlock a hashtable: allow ht_array changes again.
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* Table will be resized (shrink) when necessary.
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* This must balance a call to hash_lock().
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*/
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void hash_unlock(ht)
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hashtab_T *ht;
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{
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--ht->ht_locked;
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(void)hash_may_resize(ht, 0);
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}
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/*
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* Shrink a hashtable when there is too much empty space.
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* Grow a hashtable when there is not enough empty space.
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* Returns OK or FAIL (out of memory).
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*/
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static int hash_may_resize(ht, minitems)
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hashtab_T *ht;
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int minitems; /* minimal number of items */
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{
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hashitem_T temparray[HT_INIT_SIZE];
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hashitem_T *oldarray, *newarray;
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hashitem_T *olditem, *newitem;
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unsigned newi;
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int todo;
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long_u oldsize, newsize;
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long_u minsize;
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long_u newmask;
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hash_T perturb;
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/* Don't resize a locked table. */
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if (ht->ht_locked > 0)
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return OK;
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#ifdef HT_DEBUG
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if (ht->ht_used > ht->ht_filled)
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EMSG("hash_may_resize(): more used than filled");
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if (ht->ht_filled >= ht->ht_mask + 1)
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EMSG("hash_may_resize(): table completely filled");
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#endif
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if (minitems == 0) {
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/* Return quickly for small tables with at least two NULL items. NULL
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* items are required for the lookup to decide a key isn't there. */
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if (ht->ht_filled < HT_INIT_SIZE - 1
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&& ht->ht_array == ht->ht_smallarray)
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return OK;
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/*
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* Grow or refill the array when it's more than 2/3 full (including
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* removed items, so that they get cleaned up).
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* Shrink the array when it's less than 1/5 full. When growing it is
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* at least 1/4 full (avoids repeated grow-shrink operations)
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*/
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oldsize = ht->ht_mask + 1;
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if (ht->ht_filled * 3 < oldsize * 2 && ht->ht_used > oldsize / 5)
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return OK;
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if (ht->ht_used > 1000)
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minsize = ht->ht_used * 2; /* it's big, don't make too much room */
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else
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minsize = ht->ht_used * 4; /* make plenty of room */
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} else {
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/* Use specified size. */
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if ((long_u)minitems < ht->ht_used) /* just in case... */
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minitems = (int)ht->ht_used;
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minsize = minitems * 3 / 2; /* array is up to 2/3 full */
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}
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newsize = HT_INIT_SIZE;
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while (newsize < minsize) {
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newsize <<= 1; /* make sure it's always a power of 2 */
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if (newsize == 0)
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return FAIL; /* overflow */
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}
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if (newsize == HT_INIT_SIZE) {
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/* Use the small array inside the hashdict structure. */
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newarray = ht->ht_smallarray;
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if (ht->ht_array == newarray) {
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/* Moving from ht_smallarray to ht_smallarray! Happens when there
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* are many removed items. Copy the items to be able to clean up
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* removed items. */
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mch_memmove(temparray, newarray, sizeof(temparray));
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oldarray = temparray;
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} else
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oldarray = ht->ht_array;
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} else {
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/* Allocate an array. */
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newarray = (hashitem_T *)alloc((unsigned)
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(sizeof(hashitem_T) * newsize));
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if (newarray == NULL) {
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/* Out of memory. When there are NULL items still return OK.
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* Otherwise set ht_error, because lookup may result in a hang if
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* we add another item. */
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if (ht->ht_filled < ht->ht_mask)
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return OK;
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ht->ht_error = TRUE;
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return FAIL;
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}
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oldarray = ht->ht_array;
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}
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vim_memset(newarray, 0, (size_t)(sizeof(hashitem_T) * newsize));
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/*
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* Move all the items from the old array to the new one, placing them in
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* the right spot. The new array won't have any removed items, thus this
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* is also a cleanup action.
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*/
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newmask = newsize - 1;
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todo = (int)ht->ht_used;
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for (olditem = oldarray; todo > 0; ++olditem)
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if (!HASHITEM_EMPTY(olditem)) {
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/*
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* The algorithm to find the spot to add the item is identical to
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* the algorithm to find an item in hash_lookup(). But we only
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* need to search for a NULL key, thus it's simpler.
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*/
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newi = (unsigned)(olditem->hi_hash & newmask);
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newitem = &newarray[newi];
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if (newitem->hi_key != NULL)
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for (perturb = olditem->hi_hash;; perturb >>= PERTURB_SHIFT) {
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newi = (unsigned)((newi << 2U) + newi + perturb + 1U);
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newitem = &newarray[newi & newmask];
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if (newitem->hi_key == NULL)
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break;
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}
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*newitem = *olditem;
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--todo;
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}
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if (ht->ht_array != ht->ht_smallarray)
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vim_free(ht->ht_array);
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ht->ht_array = newarray;
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ht->ht_mask = newmask;
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ht->ht_filled = ht->ht_used;
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ht->ht_error = FALSE;
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return OK;
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}
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/*
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* Get the hash number for a key.
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* If you think you know a better hash function: Compile with HT_DEBUG set and
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* run a script that uses hashtables a lot. Vim will then print statistics
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* when exiting. Try that with the current hash algorithm and yours. The
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* lower the percentage the better.
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*/
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hash_T hash_hash(key)
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char_u *key;
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{
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hash_T hash;
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char_u *p;
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if ((hash = *key) == 0)
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return (hash_T)0; /* Empty keys are not allowed, but we don't
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want to crash if we get one. */
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p = key + 1;
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/* A simplistic algorithm that appears to do very well.
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* Suggested by George Reilly. */
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while (*p != NUL)
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hash = hash * 101 + *p++;
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return hash;
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}
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Reference in New Issue
Block a user