On Fri, 16 Sep 2011 08:50:26 -0400
Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> wrote:
> Since converting 2 ascii hex digits into a byte with error checks
> is commonly used, we can replace multiple hex_to_bin() calls with
> a single call to unpack_hex_byte().
>
> Changelog:
> - Error checking added based on Tetsuo Handa's patch.
> - Moved the hex2bin code here, making it into a static inline function.
> (Andy Shevchenko's request.)
Why, on earth? Not for performance reasons - the code is already quite
inefficient.
> Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> ---
> include/linux/kernel.h | 21 +++++++++++++++++++++
> 1 files changed, 21 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 46ac9a5..d8ea13b 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -385,6 +385,27 @@ extern int hex_to_bin(char ch);
> extern void hex2bin(u8 *dst, const char *src, size_t count);
>
> /*
> + * unpack_hex_byte - convert 2 asii hex digits into a byte
> + * @byte: binary result
> + * @buf: ascii hexadecimal byte string
> + */
> +static inline bool unpack_hex_byte(u8 *byte, const char *buf)
> +{
> + int hi, lo;
> +
> + hi = hex_to_bin(buf[0]);
> + if (hi < 0)
> + return false;
> +
> + lo = hex_to_bin(buf[1]);
> + if (lo < 0)
> + return false;
> +
> + *byte = (hi << 4) | lo;
> + return true;
> +}
Putting the return value into *byte is inefficient too - it forces the
compiler to place the return value into addressible storage (ie: into a
stack temporary). Maybe the compiler can avoid doing that if the code
is inlined, but the code shouldn't be inlined :(
The return value is undocumented.
Why not copy the hex2bin return value semantics rather than creating a
new scheme? Returning "bool false" in response to an error is very
unconventional and unexpected. Kernel code returns a negative value on
error.
Wouldn't it be better to fix hex2bin() so that it returns -1 on error?
Then the above function becomes a one-liner:
return hex2bin(dst, src, 2);
Finally, the name is poor. It starts with "unpack_", so it belongs to
the "unpack" subsystem. There's no such thing. Something like
hex_byte_to_bin() would be better.
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