cache-tree: sort the subtree entries.

Not that this makes practical performance difference; the kernel tree
for example has 200 or so directories that have subdirectory, and the
largest ones have 57 of them (fs and drivers).  With a test to apply
600 patches with git-apply and git-write-tree, this did not make more
than one per-cent of a difference, but it is a good cleanup.

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/cache-tree.c b/cache-tree.c
index 2146723..d8438d6 100644 (file)
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -19,38 +19,75 @@ void cache_tree_free(struct cache_tree **it_p)
        if (!it)
                return;
        for (i = 0; i < it->subtree_nr; i++)
-               cache_tree_free(&it->down[i]->cache_tree);
+               if (it->down[i])
+                       cache_tree_free(&it->down[i]->cache_tree);
        free(it->down);
        free(it);
        *it_p = NULL;
 }
 
+static int subtree_name_cmp(const char *one, int onelen,
+                           const char *two, int twolen)
+{
+       if (onelen < twolen)
+               return -1;
+       if (twolen < onelen)
+               return 1;
+       return memcmp(one, two, onelen);
+}
+
+static int subtree_pos(struct cache_tree *it, const char *path, int pathlen)
+{
+       struct cache_tree_sub **down = it->down;
+       int lo, hi;
+       lo = 0;
+       hi = it->subtree_nr;
+       while (lo < hi) {
+               int mi = (lo + hi) / 2;
+               struct cache_tree_sub *mdl = down[mi];
+               int cmp = subtree_name_cmp(path, pathlen,
+                                          mdl->name, mdl->namelen);
+               if (!cmp)
+                       return mi;
+               if (cmp < 0)
+                       hi = mi;
+               else
+                       lo = mi + 1;
+       }
+       return -lo-1;
+}
+
 static struct cache_tree_sub *find_subtree(struct cache_tree *it,
                                           const char *path,
                                           int pathlen,
                                           int create)
 {
-       int i;
        struct cache_tree_sub *down;
-       for (i = 0; i < it->subtree_nr; i++) {
-               down = it->down[i];
-               if (down->namelen == pathlen &&
-                   !memcmp(down->name, path, pathlen))
-                       return down;
-       }
+       int pos = subtree_pos(it, path, pathlen);
+       if (0 <= pos)
+               return it->down[pos];
        if (!create)
                return NULL;
+
+       pos = -pos-1;
        if (it->subtree_alloc <= it->subtree_nr) {
                it->subtree_alloc = alloc_nr(it->subtree_alloc);
                it->down = xrealloc(it->down, it->subtree_alloc *
                                    sizeof(*it->down));
        }
+       it->subtree_nr++;
+
        down = xmalloc(sizeof(*down) + pathlen + 1);
-       down->cache_tree = NULL; /* cache_tree(); */
+       down->cache_tree = NULL;
        down->namelen = pathlen;
        memcpy(down->name, path, pathlen);
-       down->name[pathlen] = 0; /* not strictly needed */
-       it->down[it->subtree_nr++] = down;
+       down->name[pathlen] = 0;
+
+       if (pos < it->subtree_nr)
+               memmove(it->down + pos + 1,
+                       it->down + pos,
+                       sizeof(down) * (it->subtree_nr - pos - 1));
+       it->down[pos] = down;
        return down;
 }
 
@@ -72,25 +109,21 @@ void cache_tree_invalidate_path(struct cache_tree *it, const char *path)
        slash = strchr(path, '/');
        it->entry_count = -1;
        if (!slash) {
-               int i;
+               int pos;
                namelen = strlen(path);
-               for (i = 0; i < it->subtree_nr; i++) {
-                       if (it->down[i]->namelen == namelen &&
-                           !memcmp(it->down[i]->name, path, namelen))
-                               break;
-               }
-               if (i < it->subtree_nr) {
-                       cache_tree_free(&it->down[i]->cache_tree);
-                       free(it->down[i]);
+               pos = subtree_pos(it, path, namelen);
+               if (0 <= pos) {
+                       cache_tree_free(&it->down[pos]->cache_tree);
+                       free(it->down[pos]);
                        /* 0 1 2 3 4 5
                         *       ^     ^subtree_nr = 6
-                        *       i
+                        *       pos
                         * move 4 and 5 up one place (2 entries)
-                        * 2 = 6 - 3 - 1 = subtree_nr - i - 1
+                        * 2 = 6 - 3 - 1 = subtree_nr - pos - 1
                         */
-                       memmove(it->down+i, it->down+i+1,
+                       memmove(it->down+pos, it->down+pos+1,
                                sizeof(struct cache_tree_sub *) *
-                               (it->subtree_nr - i - 1));
+                               (it->subtree_nr - pos - 1));
                        it->subtree_nr--;
                }
                return;
@@ -364,6 +397,12 @@ static void *write_one(struct cache_tree *it,
        }
        for (i = 0; i < it->subtree_nr; i++) {
                struct cache_tree_sub *down = it->down[i];
+               if (i) {
+                       struct cache_tree_sub *prev = it->down[i-1];
+                       if (subtree_name_cmp(down->name, down->namelen,
+                                            prev->name, prev->namelen) <= 0)
+                               die("fatal - unsorted cache subtree");
+               }
                buffer = write_one(down->cache_tree, down->name, down->namelen,
                                   buffer, size, offset);
        }
@@ -435,14 +474,15 @@ static struct cache_tree *read_one(const char **buffer, unsigned long *size_p)
        for (i = 0; i < subtree_nr; i++) {
                /* read each subtree */
                struct cache_tree *sub;
+               struct cache_tree_sub *subtree;
                const char *name = buf;
                int namelen;
                sub = read_one(&buf, &size);
                if (!sub)
                        goto free_return;
                namelen = strlen(name);
-               it->down[i] = find_subtree(it, name, namelen, 1);
-               it->down[i]->cache_tree = sub;
+               subtree = find_subtree(it, name, namelen, 1);
+               subtree->cache_tree = sub;
        }
        if (subtree_nr != it->subtree_nr)
                die("cache-tree: internal error");