Teach tree_entry_interesting() that the tree entries are sorted.

When we are looking at a tree entry with pathspecs, if all the
pathspecs sort strictly earlier than the entry we are currently
looking at, there is no way later entries in the same tree would
match our pathspecs, because the entries are sorted.

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

tree-diff.c

@@ -81,6 +81,7 @@ static int tree_entry_interesting(struct tree_desc *desc, const char *base, int
 	unsigned mode;
 	int i;
 	int pathlen;
+	int never_interesting = -1;
 
 	if (!opt->nr_paths)
 		return 1;
@@ -89,9 +90,10 @@ static int tree_entry_interesting(struct tree_desc *desc, const char *base, int
 
 	pathlen = tree_entry_len(path, sha1);
 
-	for (i=0; i < opt->nr_paths; i++) {
+	for (i = 0; i < opt->nr_paths; i++) {
 		const char *match = opt->paths[i];
 		int matchlen = opt->pathlens[i];
+		int m;
 
 		if (baselen >= matchlen) {
 			/* If it doesn't match, move along... */
@@ -109,6 +111,30 @@ static int tree_entry_interesting(struct tree_desc *desc, const char *base, int
 		match += baselen;
 		matchlen -= baselen;
 
+		/*
+		 * Does match sort strictly earlier than path with their
+		 * common parts?
+		 */
+		m = strncmp(match, path,
+			    (matchlen < pathlen) ? matchlen : pathlen);
+		if (m < 0)
+			continue;
+
+		/*
+		 * If we come here even once, that means there is at
+		 * least one pathspec that would sort equal to or
+		 * later than the path we are currently looking at.
+		 * In other words, if we have never reached this point
+		 * after iterating all pathspecs, it means all
+		 * pathspecs are either outside of base, or inside the
+		 * base but sorts strictly earlier than the current
+		 * one.  In either case, they will never match the
+		 * subsequent entries.  In such a case, we initialized
+		 * the variable to -1 and that is what will be
+		 * returned, allowing the caller to terminate early.
+		 */
+		never_interesting = 0;
+
 		if (pathlen > matchlen)
 			continue;
 
@@ -119,12 +145,15 @@ static int tree_entry_interesting(struct tree_desc *desc, const char *base, int
 				continue;
 		}
 
-		if (strncmp(path, match, pathlen))
-			continue;
-
-		return 1;
+		/*
+		 * If common part matched earlier then it is a hit,
+		 * because we rejected the case where path is not a
+		 * leading directory and is shorter than match.
+		 */
+		if (!m)
+			return 1;
 	}
-	return 0; /* No matches */
+	return never_interesting; /* No matches */
 }
 
 /* A whole sub-tree went away or appeared */