From f4afb4f4e3e9af626ad695c87e4f9aaa780b29ec Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Thu, 6 Jun 2013 11:40:37 -0400 Subject: [PATCH] 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" --- fs/ext4/balloc.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c index d0f13ea..5833939 100644 --- 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) -- 2.7.4