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

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Message-ID: <20150511195310.3608.qmail@ns.horizon.com>
Date:	11 May 2015 15:53:10 -0400
From:	"George Spelvin" <linux@...izon.com>
To:	joe@...ches.com, linux@...musvillemoes.dk
Cc:	linux-kernel@...r.kernel.org, linux@...izon.com
Subject: [PATCH 1/2] lib/vsprintf.c: Simplify uuid_string()

>From a53aa64b7b508d1f7cddbad556fb94f2c9c0191f Mon Sep 17 00:00:00 2001
From: George Spelvin <linux@...izon.com>
Date: Mon, 11 May 2015 13:05:55 -0400
Subject: [PATCH 1/2] lib/vsprintf.c: Simplify uuid_string()

Rather than have a second pass to upcase the buffer, just make the
hex lookup table variable.

I suspect it's a speedup, but since this is not hot code, the important
part is that it shrinks the function from 332 to 256 bytes.

Signed-off-by: George Spelvin <linux@...izon.com>
---
With apologies for the un-compilable intermediate state of the draft.

 lib/vsprintf.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 452e4a16..4c4f9055 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1270,21 +1270,23 @@ char *uuid_string(char *buf, char *end, const u8 *addr,
 	static const u8 be[16] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
 	static const u8 le[16] = {3,2,1,0,5,4,7,6,8,9,10,11,12,13,14,15};
 	const u8 *index = be;
-	bool uc = false;
+	const char *hex = hex_asc;
 
 	switch (*(++fmt)) {
 	case 'L':
-		uc = true;		/* fall-through */
+		hex = hex_asc_upper;	/* fall-through */
 	case 'l':
 		index = le;
 		break;
 	case 'B':
-		uc = true;
+		hex = hex_asc_upper;
 		break;
 	}
 
 	for (i = 0; i < 16; i++) {
-		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:
@@ -1297,13 +1299,6 @@ char *uuid_string(char *buf, char *end, const u8 *addr,
 
 	*p = 0;
 
-	if (uc) {
-		p = uuid;
-		do {
-			*p = toupper(*p);
-		} while (*(++p));
-	}
-
 	return string(buf, end, uuid, spec);
 }
 
-- 
2.1.4

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