+#define FC_CACHE_MIN_MMAP 1024
+
+/*
+ * Skip list element, make sure the 'next' pointer is the last thing
+ * in the structure, it will be allocated large enough to hold all
+ * of the necessary pointers
+ */
+
+typedef struct _FcCacheSkip FcCacheSkip;
+
+struct _FcCacheSkip {
+ FcCache *cache;
+ int ref;
+ intptr_t size;
+ dev_t cache_dev;
+ ino_t cache_ino;
+ time_t cache_mtime;
+ FcCacheSkip *next[1];
+};
+
+/*
+ * The head of the skip list; pointers for every possible level
+ * in the skip list, plus the largest level in the list
+ */
+
+#define FC_CACHE_MAX_LEVEL 16
+
+static FcCacheSkip *fcCacheChains[FC_CACHE_MAX_LEVEL];
+static int fcCacheMaxLevel;
+
+/*
+ * Generate a random level number, distributed
+ * so that each level is 1/4 as likely as the one before
+ *
+ * Note that level numbers run 1 <= level <= MAX_LEVEL
+ */
+static int
+random_level (void)
+{
+ /* tricky bit -- each bit is '1' 75% of the time */
+ long int bits = random () | random ();
+ int level = 0;
+
+ while (++level < FC_CACHE_MAX_LEVEL)
+ {
+ if (bits & 1)
+ break;
+ bits >>= 1;
+ }
+ return level;
+}
+
+/*
+ * Insert cache into the list
+ */
+static FcBool
+FcCacheInsert (FcCache *cache, struct stat *cache_stat)
+{
+ FcCacheSkip **update[FC_CACHE_MAX_LEVEL];
+ FcCacheSkip *s, **next;
+ int i, level;
+
+ /*
+ * Find links along each chain
+ */
+ next = fcCacheChains;
+ for (i = fcCacheMaxLevel; --i >= 0; )
+ {
+ for (; (s = next[i]); next = s->next)
+ if (s->cache > cache)
+ break;
+ update[i] = &next[i];
+ }
+
+ /*
+ * Create new list element
+ */
+ level = random_level ();
+ if (level > fcCacheMaxLevel)
+ {
+ level = fcCacheMaxLevel + 1;
+ update[fcCacheMaxLevel] = &fcCacheChains[fcCacheMaxLevel];
+ fcCacheMaxLevel = level;
+ }
+
+ s = malloc (sizeof (FcCacheSkip) + (level - 1) * sizeof (FcCacheSkip *));
+ if (!s)
+ return FcFalse;
+
+ s->cache = cache;
+ s->size = cache->size;
+ s->ref = 1;
+ s->cache_dev = cache_stat->st_dev;
+ s->cache_ino = cache_stat->st_ino;
+ s->cache_mtime = cache_stat->st_mtime;
+
+ /*
+ * Insert into all fcCacheChains
+ */
+ for (i = 0; i < level; i++)
+ {
+ s->next[i] = *update[i];
+ *update[i] = s;
+ }
+ return FcTrue;
+}
+
+static FcCacheSkip *
+FcCacheFindByAddr (void *object)
+{
+ int i;
+ FcCacheSkip **next = fcCacheChains;
+ FcCacheSkip *s;
+
+ /*
+ * Walk chain pointers one level at a time
+ */
+ for (i = fcCacheMaxLevel; --i >= 0;)
+ while (next[i] && (char *) object >= ((char *) next[i]->cache + next[i]->size))
+ next = next[i]->next;
+ /*
+ * Here we are
+ */
+ s = next[0];
+ if (s && (char *) object < ((char *) s->cache + s->size))
+ return s;
+ return NULL;
+}
+
+static void
+FcCacheRemove (FcCache *cache)
+{
+ FcCacheSkip **update[FC_CACHE_MAX_LEVEL];
+ FcCacheSkip *s, **next;
+ int i;
+
+ /*
+ * Find links along each chain
+ */
+ next = fcCacheChains;
+ for (i = fcCacheMaxLevel; --i >= 0; )
+ {
+ for (; (s = next[i]); next = s->next)
+ if (s->cache >= cache)
+ break;
+ update[i] = &next[i];
+ }
+ s = next[0];
+ assert (s->cache == cache);
+ for (i = 0; i < fcCacheMaxLevel && *update[i] == s; i++)
+ *update[i] = s->next[i];
+ while (fcCacheMaxLevel > 0 && fcCacheChains[fcCacheMaxLevel - 1] == NULL)
+ fcCacheMaxLevel--;
+ free (s);
+}
+
+static FcCache *
+FcCacheFindByStat (struct stat *cache_stat)
+{
+ FcCacheSkip *s;
+
+ for (s = fcCacheChains[0]; s; s = s->next[0])
+ if (s->cache_dev == cache_stat->st_dev &&
+ s->cache_ino == cache_stat->st_ino &&
+ s->cache_mtime == cache_stat->st_mtime)
+ return s->cache;
+ return NULL;
+}
+