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

[Andy Shevchenko]

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	Â-9.6%
> thumb	220	160	-60	-27.3%
> arm64	296	244	-52	-17.6%
> 
> Signed-off-by: George Spelvin <linux@xxxxxxxxxxx>
> ---
> Âlib/vsprintf.c | 16 ++++++++--------
> Â1 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,
> Â	char *p = uuid;
> Â	int i;
> Â	const u8 *index = uuid_be_index;
> -	bool uc = false;
> +	const char *hex = hex_asc;
> Â
> -	switch (*(++fmt)) {
> +	switch (fmt[1]) {
> Â	case 'L':
> -		uc = true;		/* fall-through */
> +		hex = hex_asc_upper;	/* fall-through */
> Â	case 'l':
> Â		index = uuid_le_index;
> Â		break;
> Â	case 'B':
> -		uc = true;
> +		hex = hex_asc_upper;
> Â		break;
> Â	}
> Â
> Â	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?


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

-- 
Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Intel Finland Oy