Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753989AbbEKQcf (ORCPT ); Mon, 11 May 2015 12:32:35 -0400 Received: from ns.horizon.com ([71.41.210.147]:53901 "HELO ns.horizon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751208AbbEKQcc (ORCPT ); Mon, 11 May 2015 12:32:32 -0400 Date: 11 May 2015 12:32:30 -0400 Message-ID: <20150511163230.14333.qmail@ns.horizon.com> From: "George Spelvin" To: linux@rasmusvillemoes.dk Subject: [RFC PATCH] lib/vsprintf.c: Simplify uuid_string() Cc: linux@horizon.com, linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4235 Lines: 149 I didn't see your decimal print changes before they went in, but great work! That's a real "why didn't I think of that?" change. Anyway, merging some local patches I have with that prompted me to look over that file and I came up with the following two patches which might be interesting. RFC until I build a test harness and made sure there aren't any stupid bugs, but the ideas are simple enough. They're so small I'm breaking protocol and including them both in the same e-mail. >From 065a49efdf601acdf8f9c2689259a4210a527da0 Mon Sep 17 00:00:00 2001 From: George Spelvin Date: Mon, 11 May 2015 08:09:39 -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 --- lib/vsprintf.c | 17 ++++++----------- 1 file changed, 6 insertions(+), 11 deletions(-) diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 452e4a16..de7f5bde 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[x >> 4]; + *p++ = hex[x & 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 >From 744056f73bb5625d52de61605b31300ba3d3fbc6 Mon Sep 17 00:00:00 2001 From: George Spelvin Date: Mon, 11 May 2015 10:46:52 -0400 Subject: [PATCH 2/2] lib/vsprintf.c: Further simplify uuid_string(). Make the endianness permutation table do double duty by having it list not source offsets, but destination offsets. Thus, it both puts the bytes in the right order and skips the hyphens. This further shrinks the code from 256 to 214 bytes. Eliminating erratic branches probably helps speed, too. Signed-off-by: George Spelvin --- lib/vsprintf.c | 25 +++++++++---------------- 1 file changed, 9 insertions(+), 16 deletions(-) diff --git a/lib/vsprintf.c b/lib/vsprintf.c index de7f5bde..38c1d87e 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -1265,10 +1265,9 @@ char *uuid_string(char *buf, char *end, const u8 *addr, struct printf_spec spec, const char *fmt) { char uuid[sizeof("xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx")]; - char *p = uuid; int i; - 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}; + static const u8 be[16] = {0,2,4,6,9,11,14,16,19,21,24,26,28,30,32,34}; + static const u8 le[16] = {6,4,2,0,11,9,16,14,19,21,24,26,28,30,32,34}; const u8 *index = be; const char *hex = hex_asc; @@ -1284,20 +1283,14 @@ char *uuid_string(char *buf, char *end, const u8 *addr, } for (i = 0; i < 16; i++) { - u8 byte = addr[index[i]]; - *p++ = hex[x >> 4]; - *p++ = hex[x & 0x0f]; - switch (i) { - case 3: - case 5: - case 7: - case 9: - *p++ = '-'; - break; - } - } + u8 byte = addr[i]; + char *p = uuid + index[i]; - *p = 0; + p[0] = hex[byte >> 4]; + p[1] = hex[byte & 0x0f]; + } + uuid[23] = uuid[18] = uuid[13] = uuid[8] = '-'; + uuid[36] = 0; return string(buf, end, uuid, spec); } -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/