Re: [PATCH,RFC] ext3: Add support for non-native signed/unsigned htree hash algorithms

Matt Mackall
2008-10-22T18:48:20Z

On Mon, 2008-10-20 at 23:43 -0400, Theodore Ts'o wrote:
> The original ext3 hash algorithms assumed that variables of type char
> were signed, as God and K&R intended. Unfortunately, this assumption
> is not true on some architectures. Userspace support for marking
> filesystems with non-native signed/unsigned chars was added two years
> ago, but the kernel-side support was never added (until now).
>
> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
> Cc: akpm@linux-foundation.org
> Cc: linux-kernel@vger.kernel.org
> ---
> fs/ext3/hash.c | 42 +++++++++++++++++++++++++++++++++---------
> fs/ext3/namei.c | 7 +++++++
> fs/ext3/super.c | 15 +++++++++++++++
> include/linux/ext3_fs.h | 28 +++++++++++++++++++++++++++-
> include/linux/ext3_fs_sb.h | 1 +
> 5 files changed, 83 insertions(+), 10 deletions(-)
>
> diff --git a/fs/ext3/hash.c b/fs/ext3/hash.c
> index c30e149..855eacb 100644
> --- a/fs/ext3/hash.c
> +++ b/fs/ext3/hash.c
> @@ -35,11 +35,20 @@ static void TEA_transform(__u32 buf[4], __u32 const in[])
>
>
> /* The old legacy hash */
> -static __u32 dx_hack_hash (const char *name, int len)
> +static __u32 dx_hack_hash (const char *name, int len, int unsigned_flag)
> {
> - __u32 hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
> + __u32 hash, hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
> + const unsigned char *ucp = (const unsigned char *) name;
> + const signed char *scp = (const signed char *) name;
> + int c;
> +
> while (len--) {
> - __u32 hash = hash1 + (hash0 ^ (*name++ * 7152373));
> + if (unsigned_flag)
> + c = (int) *ucp++;
> + else
> + c = (int) *scp++;

Branch in the inner loop? Space after typecast?

> for (i=0; i < len; i++) {
> if ((i % 4) == 0)
> val = pad;
> - val = msg[i] + (val << 8);
> + if (unsigned_flag)
> + c = (int) ucp[i];
> + else
> + c = (int) scp[i];
> +
> + val = c + (val << 8);

And here.

--
Mathematics is the supreme nostalgia of our time.