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

George Spelvin
2016-06-04T05:14:14Z

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];
switch (i) {
case 3:
case 5:
--
2.8.1