+/*
+ * Given a name and sha1 pair, if the dircache tells us the file in
+ * the work tree has that object contents, return true, so that
+ * prepare_temp_file() does not have to inflate and extract.
+ */
+static int work_tree_matches(const char *name, const unsigned char *sha1)
+{
+ struct cache_entry *ce;
+ struct stat st;
+ int pos, len;
+
+ /* We do not read the cache ourselves here, because the
+ * benchmark with my previous version that always reads cache
+ * shows that it makes things worse for diff-tree comparing
+ * two linux-2.6 kernel trees in an already checked out work
+ * tree. This is because most diff-tree comparisons deal with
+ * only a small number of files, while reading the cache is
+ * expensive for a large project, and its cost outweighs the
+ * savings we get by not inflating the object to a temporary
+ * file. Practically, this code only helps when we are used
+ * by diff-cache --cached, which does read the cache before
+ * calling us.
+ */
+ if (!active_cache)
+ return 0;
+
+ len = strlen(name);
+ pos = cache_name_pos(name, len);
+ if (pos < 0)
+ return 0;
+ ce = active_cache[pos];
+ if ((lstat(name, &st) < 0) ||
+ !S_ISREG(st.st_mode) ||
+ ce_match_stat(ce, &st) ||
+ memcmp(sha1, ce->sha1, 20))
+ return 0;
+ return 1;
+}
+
+static void prep_temp_blob(struct diff_tempfile *temp,
+ void *blob,
+ unsigned long size,
+ unsigned char *sha1,
+ int mode)
+{
+ int fd;
+
+ strcpy(temp->tmp_path, ".diff_XXXXXX");
+ fd = mkstemp(temp->tmp_path);
+ if (fd < 0)
+ die("unable to create temp-file");
+ if (write(fd, blob, size) != size)
+ die("unable to write temp-file");
+ close(fd);
+ temp->name = temp->tmp_path;
+ strcpy(temp->hex, sha1_to_hex(sha1));
+ temp->hex[40] = 0;
+ sprintf(temp->mode, "%06o", mode);
+}
+