From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755414AbbBTXVv (ORCPT ); Fri, 20 Feb 2015 18:21:51 -0500 Received: from mail-lb0-f180.google.com ([209.85.217.180]:42192 "EHLO mail-lb0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755010AbbBTXVt (ORCPT ); Fri, 20 Feb 2015 18:21:49 -0500 From: Rasmus Villemoes To: Andrew Morton , Rasmus Villemoes , "Peter Zijlstra (Intel)" , Tejun Heo Cc: linux-kernel@vger.kernel.org Subject: [PATCH 1/4] lib/vsprintf.c: Eliminate some branches Date: Sat, 21 Feb 2015 00:21:16 +0100 Message-Id: <1424474479-25543-2-git-send-email-linux@rasmusvillemoes.dk> X-Mailer: git-send-email 2.1.3 In-Reply-To: <1424474479-25543-1-git-send-email-linux@rasmusvillemoes.dk> References: <1424474479-25543-1-git-send-email-linux@rasmusvillemoes.dk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Since FORMAT_TYPE_INT is simply 1 more than FORMAT_TYPE_UINT, and similarly for BYTE/UBYTE, SHORT/USHORT, LONG/ULONG, we can eliminate a few instructions by making SIGN have the value 1 instead of 2, and then use arithmetic instead of branches for computing the right spec->type. It's a little hacky, but certainly in the same spirit as SMALL needing to have the value 0x20. For example for the spec->qualifier == 'l' case, gcc now generates 75e: 0f b6 53 01 movzbl 0x1(%rbx),%edx 762: 83 e2 01 and $0x1,%edx 765: 83 c2 09 add $0x9,%edx 768: 88 13 mov %dl,(%rbx) instead of 763: 0f b6 53 01 movzbl 0x1(%rbx),%edx 767: 83 e2 02 and $0x2,%edx 76a: 80 fa 01 cmp $0x1,%dl 76d: 19 d2 sbb %edx,%edx 76f: 83 c2 0a add $0xa,%edx 772: 88 13 mov %dl,(%rbx) Signed-off-by: Rasmus Villemoes --- lib/vsprintf.c | 30 +++++++++++------------------- 1 file changed, 11 insertions(+), 19 deletions(-) diff --git a/lib/vsprintf.c b/lib/vsprintf.c index b235c96167d3..318d583fe862 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -340,8 +340,8 @@ int num_to_str(char *buf, int size, unsigned long long num) return len; } -#define ZEROPAD 1 /* pad with zero */ -#define SIGN 2 /* unsigned/signed long */ +#define SIGN 1 /* unsigned/signed, must be 1 */ +#define ZEROPAD 2 /* pad with zero */ #define PLUS 4 /* show plus */ #define SPACE 8 /* space if plus */ #define LEFT 16 /* left justified */ @@ -447,7 +447,7 @@ char *number(char *buf, char *end, unsigned long long num, spec.precision = i; /* leading space padding */ spec.field_width -= spec.precision; - if (!(spec.flags & (ZEROPAD+LEFT))) { + if (!(spec.flags & (ZEROPAD | LEFT))) { while (--spec.field_width >= 0) { if (buf < end) *buf = ' '; @@ -1738,29 +1738,21 @@ qualifier: if (spec->qualifier == 'L') spec->type = FORMAT_TYPE_LONG_LONG; else if (spec->qualifier == 'l') { - if (spec->flags & SIGN) - spec->type = FORMAT_TYPE_LONG; - else - spec->type = FORMAT_TYPE_ULONG; + BUILD_BUG_ON(FORMAT_TYPE_ULONG + SIGN != FORMAT_TYPE_LONG); + spec->type = FORMAT_TYPE_ULONG + (spec->flags & SIGN); } else if (_tolower(spec->qualifier) == 'z') { spec->type = FORMAT_TYPE_SIZE_T; } else if (spec->qualifier == 't') { spec->type = FORMAT_TYPE_PTRDIFF; } else if (spec->qualifier == 'H') { - if (spec->flags & SIGN) - spec->type = FORMAT_TYPE_BYTE; - else - spec->type = FORMAT_TYPE_UBYTE; + BUILD_BUG_ON(FORMAT_TYPE_UBYTE + SIGN != FORMAT_TYPE_BYTE); + spec->type = FORMAT_TYPE_UBYTE + (spec->flags & SIGN); } else if (spec->qualifier == 'h') { - if (spec->flags & SIGN) - spec->type = FORMAT_TYPE_SHORT; - else - spec->type = FORMAT_TYPE_USHORT; + BUILD_BUG_ON(FORMAT_TYPE_USHORT + SIGN != FORMAT_TYPE_SHORT); + spec->type = FORMAT_TYPE_USHORT + (spec->flags & SIGN); } else { - if (spec->flags & SIGN) - spec->type = FORMAT_TYPE_INT; - else - spec->type = FORMAT_TYPE_UINT; + BUILD_BUG_ON(FORMAT_TYPE_UINT + SIGN != FORMAT_TYPE_INT); + spec->type = FORMAT_TYPE_UINT + (spec->flags & SIGN); } return ++fmt - start; -- 2.1.3