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ext4: optimize test_root()

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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>
This commit is contained in:
Theodore Ts'o 2013-06-06 11:40:37 -04:00
parent 2f2e09eb15
commit f4afb4f4e3
1 changed files with 9 additions and 5 deletions
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14
fs/ext4/balloc.c
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@ -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) static inline int test_root(ext4_group_t a, int b)
{ {
int num = b; while (1) {
if (a < b)
while (a > num) return 0;
num *= b; if (a == b)
return num == a; return 1;
if ((a % b) != 0)
return 0;
a = a / b;
}
} }
static int ext4_group_sparse(ext4_group_t group) static int ext4_group_sparse(ext4_group_t group)