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![Junio C Hamano](/assets/img/avatar_default.png)
When we know approximately how many entries we will have in the hash-table, it makes sense to size the hash table to that number from the beginning to avoid unnecessary rehashing. * nd/preallocate-hash: Preallocate hash tables when the number of inserts are known in advance
193 lines
4.7 KiB
C
193 lines
4.7 KiB
C
/*
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* name-hash.c
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*
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* Hashing names in the index state
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*
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* Copyright (C) 2008 Linus Torvalds
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*/
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#define NO_THE_INDEX_COMPATIBILITY_MACROS
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#include "cache.h"
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/*
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* This removes bit 5 if bit 6 is set.
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*
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* That will make US-ASCII characters hash to their upper-case
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* equivalent. We could easily do this one whole word at a time,
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* but that's for future worries.
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*/
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static inline unsigned char icase_hash(unsigned char c)
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{
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return c & ~((c & 0x40) >> 1);
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}
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static unsigned int hash_name(const char *name, int namelen)
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{
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unsigned int hash = 0x123;
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while (namelen--) {
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unsigned char c = *name++;
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c = icase_hash(c);
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hash = hash*101 + c;
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}
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return hash;
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}
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static void hash_index_entry_directories(struct index_state *istate, struct cache_entry *ce)
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{
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/*
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* Throw each directory component in the hash for quick lookup
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* during a git status. Directory components are stored with their
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* closing slash. Despite submodules being a directory, they never
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* reach this point, because they are stored without a closing slash
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* in the cache.
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*
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* Note that the cache_entry stored with the directory does not
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* represent the directory itself. It is a pointer to an existing
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* filename, and its only purpose is to represent existence of the
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* directory in the cache. It is very possible multiple directory
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* hash entries may point to the same cache_entry.
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*/
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unsigned int hash;
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void **pos;
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const char *ptr = ce->name;
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while (*ptr) {
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while (*ptr && *ptr != '/')
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++ptr;
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if (*ptr == '/') {
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++ptr;
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hash = hash_name(ce->name, ptr - ce->name);
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pos = insert_hash(hash, ce, &istate->name_hash);
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if (pos) {
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ce->dir_next = *pos;
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*pos = ce;
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}
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}
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}
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}
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static void hash_index_entry(struct index_state *istate, struct cache_entry *ce)
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{
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void **pos;
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unsigned int hash;
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if (ce->ce_flags & CE_HASHED)
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return;
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ce->ce_flags |= CE_HASHED;
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ce->next = ce->dir_next = NULL;
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hash = hash_name(ce->name, ce_namelen(ce));
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pos = insert_hash(hash, ce, &istate->name_hash);
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if (pos) {
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ce->next = *pos;
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*pos = ce;
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}
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if (ignore_case)
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hash_index_entry_directories(istate, ce);
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}
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static void lazy_init_name_hash(struct index_state *istate)
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{
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int nr;
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if (istate->name_hash_initialized)
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return;
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if (istate->cache_nr)
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preallocate_hash(&istate->name_hash, istate->cache_nr);
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for (nr = 0; nr < istate->cache_nr; nr++)
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hash_index_entry(istate, istate->cache[nr]);
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istate->name_hash_initialized = 1;
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}
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void add_name_hash(struct index_state *istate, struct cache_entry *ce)
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{
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ce->ce_flags &= ~CE_UNHASHED;
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if (istate->name_hash_initialized)
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hash_index_entry(istate, ce);
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}
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static int slow_same_name(const char *name1, int len1, const char *name2, int len2)
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{
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if (len1 != len2)
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return 0;
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while (len1) {
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unsigned char c1 = *name1++;
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unsigned char c2 = *name2++;
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len1--;
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if (c1 != c2) {
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c1 = toupper(c1);
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c2 = toupper(c2);
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if (c1 != c2)
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return 0;
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}
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}
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return 1;
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}
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static int same_name(const struct cache_entry *ce, const char *name, int namelen, int icase)
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{
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int len = ce_namelen(ce);
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/*
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* Always do exact compare, even if we want a case-ignoring comparison;
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* we do the quick exact one first, because it will be the common case.
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*/
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if (len == namelen && !cache_name_compare(name, namelen, ce->name, len))
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return 1;
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if (!icase)
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return 0;
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/*
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* If the entry we're comparing is a filename (no trailing slash), then compare
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* the lengths exactly.
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*/
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if (name[namelen - 1] != '/')
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return slow_same_name(name, namelen, ce->name, len);
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/*
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* For a directory, we point to an arbitrary cache_entry filename. Just
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* make sure the directory portion matches.
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*/
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return slow_same_name(name, namelen, ce->name, namelen < len ? namelen : len);
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}
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struct cache_entry *index_name_exists(struct index_state *istate, const char *name, int namelen, int icase)
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{
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unsigned int hash = hash_name(name, namelen);
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struct cache_entry *ce;
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lazy_init_name_hash(istate);
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ce = lookup_hash(hash, &istate->name_hash);
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while (ce) {
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if (!(ce->ce_flags & CE_UNHASHED)) {
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if (same_name(ce, name, namelen, icase))
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return ce;
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}
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if (icase && name[namelen - 1] == '/')
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ce = ce->dir_next;
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else
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ce = ce->next;
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}
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/*
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* Might be a submodule. Despite submodules being directories,
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* they are stored in the name hash without a closing slash.
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* When ignore_case is 1, directories are stored in the name hash
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* with their closing slash.
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*
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* The side effect of this storage technique is we have need to
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* remove the slash from name and perform the lookup again without
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* the slash. If a match is made, S_ISGITLINK(ce->mode) will be
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* true.
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*/
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if (icase && name[namelen - 1] == '/') {
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ce = index_name_exists(istate, name, namelen - 1, icase);
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if (ce && S_ISGITLINK(ce->ce_mode))
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return ce;
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}
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return NULL;
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}
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