+#include "cache.h"
+#include "tree-walk.h"
+
+void *fill_tree_descriptor(struct tree_desc *desc, const unsigned char *sha1)
+{
+ unsigned long size = 0;
+ void *buf = NULL;
+
+ if (sha1) {
+ buf = read_object_with_reference(sha1, "tree", &size, NULL);
+ if (!buf)
+ die("unable to read tree %s", sha1_to_hex(sha1));
+ }
+ desc->size = size;
+ desc->buf = buf;
+ return buf;
+}
+
+static int entry_compare(struct name_entry *a, struct name_entry *b)
+{
+ return base_name_compare(
+ a->path, a->pathlen, a->mode,
+ b->path, b->pathlen, b->mode);
+}
+
+static void entry_clear(struct name_entry *a)
+{
+ memset(a, 0, sizeof(*a));
+}
+
+static void entry_extract(struct tree_desc *t, struct name_entry *a)
+{
+ a->sha1 = tree_entry_extract(t, &a->path, &a->mode);
+ a->pathlen = strlen(a->path);
+}
+
+void update_tree_entry(struct tree_desc *desc)
+{
+ void *buf = desc->buf;
+ unsigned long size = desc->size;
+ int len = strlen(buf) + 1 + 20;
+
+ if (size < len)
+ die("corrupt tree file");
+ desc->buf = buf + len;
+ desc->size = size - len;
+}
+
+const unsigned char *tree_entry_extract(struct tree_desc *desc, const char **pathp, unsigned int *modep)
+{
+ void *tree = desc->buf;
+ unsigned long size = desc->size;
+ int len = strlen(tree)+1;
+ const unsigned char *sha1 = tree + len;
+ const char *path = strchr(tree, ' ');
+ unsigned int mode;
+
+ if (!path || size < len + 20 || sscanf(tree, "%o", &mode) != 1)
+ die("corrupt tree file");
+ *pathp = path+1;
+ *modep = canon_mode(mode);
+ return sha1;
+}
+
+void traverse_trees(int n, struct tree_desc *t, const char *base, traverse_callback_t callback)
+{
+ struct name_entry *entry = xmalloc(n*sizeof(*entry));
+
+ for (;;) {
+ struct name_entry entry[3];
+ unsigned long mask = 0;
+ int i, last;
+
+ last = -1;
+ for (i = 0; i < n; i++) {
+ if (!t[i].size)
+ continue;
+ entry_extract(t+i, entry+i);
+ if (last >= 0) {
+ int cmp = entry_compare(entry+i, entry+last);
+
+ /*
+ * Is the new name bigger than the old one?
+ * Ignore it
+ */
+ if (cmp > 0)
+ continue;
+ /*
+ * Is the new name smaller than the old one?
+ * Ignore all old ones
+ */
+ if (cmp < 0)
+ mask = 0;
+ }
+ mask |= 1ul << i;
+ last = i;
+ }
+ if (!mask)
+ break;
+
+ /*
+ * Update the tree entries we've walked, and clear
+ * all the unused name-entries.
+ */
+ for (i = 0; i < n; i++) {
+ if (mask & (1ul << i)) {
+ update_tree_entry(t+i);
+ continue;
+ }
+ entry_clear(entry + i);
+ }
+ callback(n, mask, entry, base);
+ }
+ free(entry);
+}
+