ext4: optimize test_root()

The test_root() function could potentially loop forever due to
overflow issues.  So rewrite test_root() to avoid this issue; as a
bonus, it is 38% faster when benchmarked via a test loop:

int main(int argc, char **argv)
{
	int  i;

	for (i = 0; i < 1 << 24; i++) {
		if (test_root(i, 7))
			printf("%d\n", i);
	}
}

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index d0f13eada0ed5799295a5378642cd3786cf32595..58339393fa6e55c689adfa375b804a108a25c924 100644 (file)
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -682,11 +682,15 @@ ext4_fsblk_t ext4_count_free_clusters(struct super_block *sb)
 
 static inline int test_root(ext4_group_t a, int b)
 {
-       int num = b;
-
-       while (a > num)
-               num *= b;
-       return num == a;
+       while (1) {
+               if (a < b)
+                       return 0;
+               if (a == b)
+                       return 1;
+               if ((a % b) != 0)
+                       return 0;
+               a = a / b;
+       }
 }
 
 static int ext4_group_sparse(ext4_group_t group)