linux-kernel - [PATCH v2 1/2] lib/vsprintf.c: Simplify uuid

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Date:	4 Jun 2016 01:14:11 -0400
From:	"George Spelvin" <linux@...encehorizons.net>
To:	andriy.shevchenko@...ux.intel.com
Cc:	bjorn@...k.no, linux-kernel@...r.kernel.org,
	linux@...encehorizons.net, matt@...eblueprint.co.uk,
	rv@...musvillemoes.dk
Subject: [PATCH v2 1/2] lib/vsprintf.c: Simplify uuid_string()

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@...izon.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