Re: [PATCH v2 1/2] lib/vsprintf.c: Simplify uuid_string()

Andy Shevchenko
2016-06-05T14:21:42Z

On Sat, 2016-06-04 at 01:14 -0400, George Spelvin wrote:
> Rather than have a second pass to upcase the buffer, just make the
> hex lookup table a variable.
>
> Removing the conditional branch from the inner loop is also a
> speedup, but since this is not hot code, the important factor
> it shrinks both source and compiled forms:
>
> Before After Delta Percentage
> x86-32 245 199 -46 -18.8%
> x86-64 246 186 -60 -24.4%
> arm 292 264 -28  -9.6%
> thumb 220 160 -60 -27.3%
> arm64 296 244 -52 -17.6%
>
> Signed-off-by: George Spelvin <linux@horizon.com>
> ---
>  lib/vsprintf.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 7332a5d7..4ee07e89 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1316,24 +1316,24 @@ char *uuid_string(char *buf, char *end, const
> u8 *addr,
>   char *p = uuid;
>   int i;
>   const u8 *index = uuid_be_index;
> - bool uc = false;
> + const char *hex = hex_asc;
>
> - switch (*(++fmt)) {
> + switch (fmt[1]) {
>   case 'L':
> - uc = true; /* fall-through */
> + hex = hex_asc_upper; /* fall-through */
>   case 'l':
>   index = uuid_le_index;
>   break;
>   case 'B':
> - uc = true;
> + hex = hex_asc_upper;
>   break;
>   }
>
>   for (i = 0; i < 16; i++) {
> - if (uc)
> - p = hex_byte_pack_upper(p, addr[index[i]]);
> - else
> - p = hex_byte_pack(p, addr[index[i]]);
> + u8 byte = addr[index[i]];
> +
> + *p++ = hex[byte >> 4];
> + *p++ = hex[byte & 0x0f];

And what prevents you to assign hex_byte_pack()/hex_byte_pack_upper()
and do one call here?

>   switch (i) {
>   case 3:
>   case 5:

--
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy