name-hash.con commit pack_one_ref(): do some cheap tests before a more expensive one (b2a8226)
   1/*
   2 * name-hash.c
   3 *
   4 * Hashing names in the index state
   5 *
   6 * Copyright (C) 2008 Linus Torvalds
   7 */
   8#define NO_THE_INDEX_COMPATIBILITY_MACROS
   9#include "cache.h"
  10
  11/*
  12 * This removes bit 5 if bit 6 is set.
  13 *
  14 * That will make US-ASCII characters hash to their upper-case
  15 * equivalent. We could easily do this one whole word at a time,
  16 * but that's for future worries.
  17 */
  18static inline unsigned char icase_hash(unsigned char c)
  19{
  20        return c & ~((c & 0x40) >> 1);
  21}
  22
  23static unsigned int hash_name(const char *name, int namelen)
  24{
  25        unsigned int hash = 0x123;
  26
  27        do {
  28                unsigned char c = *name++;
  29                c = icase_hash(c);
  30                hash = hash*101 + c;
  31        } while (--namelen);
  32        return hash;
  33}
  34
  35struct dir_entry {
  36        struct dir_entry *next;
  37        struct dir_entry *parent;
  38        struct cache_entry *ce;
  39        int nr;
  40        unsigned int namelen;
  41};
  42
  43static struct dir_entry *find_dir_entry(struct index_state *istate,
  44                const char *name, unsigned int namelen)
  45{
  46        unsigned int hash = hash_name(name, namelen);
  47        struct dir_entry *dir;
  48
  49        for (dir = lookup_hash(hash, &istate->dir_hash); dir; dir = dir->next)
  50                if (dir->namelen == namelen &&
  51                    !strncasecmp(dir->ce->name, name, namelen))
  52                        return dir;
  53        return NULL;
  54}
  55
  56static struct dir_entry *hash_dir_entry(struct index_state *istate,
  57                struct cache_entry *ce, int namelen)
  58{
  59        /*
  60         * Throw each directory component in the hash for quick lookup
  61         * during a git status. Directory components are stored with their
  62         * closing slash.  Despite submodules being a directory, they never
  63         * reach this point, because they are stored without a closing slash
  64         * in index_state.name_hash (as ordinary cache_entries).
  65         *
  66         * Note that the cache_entry stored with the dir_entry merely
  67         * supplies the name of the directory (up to dir_entry.namelen). We
  68         * track the number of 'active' files in a directory in dir_entry.nr,
  69         * so we can tell if the directory is still relevant, e.g. for git
  70         * status. However, if cache_entries are removed, we cannot pinpoint
  71         * an exact cache_entry that's still active. It is very possible that
  72         * multiple dir_entries point to the same cache_entry.
  73         */
  74        struct dir_entry *dir;
  75
  76        /* get length of parent directory */
  77        while (namelen > 0 && !is_dir_sep(ce->name[namelen - 1]))
  78                namelen--;
  79        if (namelen <= 0)
  80                return NULL;
  81
  82        /* lookup existing entry for that directory */
  83        dir = find_dir_entry(istate, ce->name, namelen);
  84        if (!dir) {
  85                /* not found, create it and add to hash table */
  86                void **pdir;
  87                unsigned int hash = hash_name(ce->name, namelen);
  88
  89                dir = xcalloc(1, sizeof(struct dir_entry));
  90                dir->namelen = namelen;
  91                dir->ce = ce;
  92
  93                pdir = insert_hash(hash, dir, &istate->dir_hash);
  94                if (pdir) {
  95                        dir->next = *pdir;
  96                        *pdir = dir;
  97                }
  98
  99                /* recursively add missing parent directories */
 100                dir->parent = hash_dir_entry(istate, ce, namelen - 1);
 101        }
 102        return dir;
 103}
 104
 105static void add_dir_entry(struct index_state *istate, struct cache_entry *ce)
 106{
 107        /* Add reference to the directory entry (and parents if 0). */
 108        struct dir_entry *dir = hash_dir_entry(istate, ce, ce_namelen(ce));
 109        while (dir && !(dir->nr++))
 110                dir = dir->parent;
 111}
 112
 113static void remove_dir_entry(struct index_state *istate, struct cache_entry *ce)
 114{
 115        /*
 116         * Release reference to the directory entry (and parents if 0).
 117         *
 118         * Note: we do not remove / free the entry because there's no
 119         * hash.[ch]::remove_hash and dir->next may point to other entries
 120         * that are still valid, so we must not free the memory.
 121         */
 122        struct dir_entry *dir = hash_dir_entry(istate, ce, ce_namelen(ce));
 123        while (dir && dir->nr && !(--dir->nr))
 124                dir = dir->parent;
 125}
 126
 127static void hash_index_entry(struct index_state *istate, struct cache_entry *ce)
 128{
 129        void **pos;
 130        unsigned int hash;
 131
 132        if (ce->ce_flags & CE_HASHED)
 133                return;
 134        ce->ce_flags |= CE_HASHED;
 135        ce->next = NULL;
 136        hash = hash_name(ce->name, ce_namelen(ce));
 137        pos = insert_hash(hash, ce, &istate->name_hash);
 138        if (pos) {
 139                ce->next = *pos;
 140                *pos = ce;
 141        }
 142
 143        if (ignore_case && !(ce->ce_flags & CE_UNHASHED))
 144                add_dir_entry(istate, ce);
 145}
 146
 147static void lazy_init_name_hash(struct index_state *istate)
 148{
 149        int nr;
 150
 151        if (istate->name_hash_initialized)
 152                return;
 153        for (nr = 0; nr < istate->cache_nr; nr++)
 154                hash_index_entry(istate, istate->cache[nr]);
 155        istate->name_hash_initialized = 1;
 156}
 157
 158void add_name_hash(struct index_state *istate, struct cache_entry *ce)
 159{
 160        /* if already hashed, add reference to directory entries */
 161        if (ignore_case && (ce->ce_flags & CE_STATE_MASK) == CE_STATE_MASK)
 162                add_dir_entry(istate, ce);
 163
 164        ce->ce_flags &= ~CE_UNHASHED;
 165        if (istate->name_hash_initialized)
 166                hash_index_entry(istate, ce);
 167}
 168
 169/*
 170 * We don't actually *remove* it, we can just mark it invalid so that
 171 * we won't find it in lookups.
 172 *
 173 * Not only would we have to search the lists (simple enough), but
 174 * we'd also have to rehash other hash buckets in case this makes the
 175 * hash bucket empty (common). So it's much better to just mark
 176 * it.
 177 */
 178void remove_name_hash(struct index_state *istate, struct cache_entry *ce)
 179{
 180        /* if already hashed, release reference to directory entries */
 181        if (ignore_case && (ce->ce_flags & CE_STATE_MASK) == CE_HASHED)
 182                remove_dir_entry(istate, ce);
 183
 184        ce->ce_flags |= CE_UNHASHED;
 185}
 186
 187static int slow_same_name(const char *name1, int len1, const char *name2, int len2)
 188{
 189        if (len1 != len2)
 190                return 0;
 191
 192        while (len1) {
 193                unsigned char c1 = *name1++;
 194                unsigned char c2 = *name2++;
 195                len1--;
 196                if (c1 != c2) {
 197                        c1 = toupper(c1);
 198                        c2 = toupper(c2);
 199                        if (c1 != c2)
 200                                return 0;
 201                }
 202        }
 203        return 1;
 204}
 205
 206static int same_name(const struct cache_entry *ce, const char *name, int namelen, int icase)
 207{
 208        int len = ce_namelen(ce);
 209
 210        /*
 211         * Always do exact compare, even if we want a case-ignoring comparison;
 212         * we do the quick exact one first, because it will be the common case.
 213         */
 214        if (len == namelen && !cache_name_compare(name, namelen, ce->name, len))
 215                return 1;
 216
 217        if (!icase)
 218                return 0;
 219
 220        return slow_same_name(name, namelen, ce->name, len);
 221}
 222
 223struct cache_entry *index_name_exists(struct index_state *istate, const char *name, int namelen, int icase)
 224{
 225        unsigned int hash = hash_name(name, namelen);
 226        struct cache_entry *ce;
 227
 228        lazy_init_name_hash(istate);
 229        ce = lookup_hash(hash, &istate->name_hash);
 230
 231        while (ce) {
 232                if (!(ce->ce_flags & CE_UNHASHED)) {
 233                        if (same_name(ce, name, namelen, icase))
 234                                return ce;
 235                }
 236                ce = ce->next;
 237        }
 238
 239        /*
 240         * When looking for a directory (trailing '/'), it might be a
 241         * submodule or a directory. Despite submodules being directories,
 242         * they are stored in the name hash without a closing slash.
 243         * When ignore_case is 1, directories are stored in a separate hash
 244         * table *with* their closing slash.
 245         *
 246         * The side effect of this storage technique is we have need to
 247         * lookup the directory in a separate hash table, and if not found
 248         * remove the slash from name and perform the lookup again without
 249         * the slash.  If a match is made, S_ISGITLINK(ce->mode) will be
 250         * true.
 251         */
 252        if (icase && name[namelen - 1] == '/') {
 253                struct dir_entry *dir = find_dir_entry(istate, name, namelen);
 254                if (dir && dir->nr)
 255                        return dir->ce;
 256
 257                ce = index_name_exists(istate, name, namelen - 1, icase);
 258                if (ce && S_ISGITLINK(ce->ce_mode))
 259                        return ce;
 260        }
 261        return NULL;
 262}
 263
 264static int free_dir_entry(void *entry, void *unused)
 265{
 266        struct dir_entry *dir = entry;
 267        while (dir) {
 268                struct dir_entry *next = dir->next;
 269                free(dir);
 270                dir = next;
 271        }
 272        return 0;
 273}
 274
 275void free_name_hash(struct index_state *istate)
 276{
 277        if (!istate->name_hash_initialized)
 278                return;
 279        istate->name_hash_initialized = 0;
 280        if (ignore_case)
 281                /* free directory entries */
 282                for_each_hash(&istate->dir_hash, free_dir_entry, NULL);
 283
 284        free_hash(&istate->name_hash);
 285        free_hash(&istate->dir_hash);
 286}