From patchwork Wed Nov 16 18:53:03 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Wilco Dijkstra X-Patchwork-Id: 17523 Received: (qmail 119651 invoked by alias); 16 Nov 2016 18:53:19 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 119632 invoked by uid 89); 16 Nov 2016 18:53:18 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=AWL, BAYES_00, RCVD_IN_DNSWL_NONE, SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=Suppose, LONG_MAX, Arent, long_max X-HELO: EUR01-VE1-obe.outbound.protection.outlook.com From: Wilco Dijkstra To: "libc-alpha@sourceware.org" CC: nd Subject: [PATCH] Improve generic rawmemchr Date: Wed, 16 Nov 2016 18:53:03 +0000 Message-ID: authentication-results: spf=none (sender IP is ) smtp.mailfrom=Wilco.Dijkstra@arm.com; x-microsoft-exchange-diagnostics: 1; AM5PR0802MB2610; 7:RHDmGtD38r4+vZ9AN+WnV7IrYwLxLm+xIaj0K793DjRj9X0IUrO+SVIYTZLUTwTfNRXv55pD/feR0ZjpkLI57WYhUkRp5uPzFS9NBtEKUImqx5vYT0jmycl1Cy0VmLhd2lXCQxK45pw9sR1iX9sZedNERvcNUeshVphfZQyso9RhDF8Kxct6/kaPz8vvwUJwukVMNMsWBj5X/zHSp1/s4Z4G2HflQ2qkk+NdMK7ja9Cx5OPGiiYY70VIuAjqgmMGFEEW2ioEP5cr0ZRS3zN+vG7bcsR35NZXUtzObYR4YGrnKaCAUqUppdYhDKeImRw9mk++NTLBsuFhnk+pfK+2Z3WzWm5TvtK0f8CWsqoQLb4= x-ms-office365-filtering-correlation-id: aac978a4-5439-4538-2ded-08d40e51cb6a x-microsoft-antispam: UriScan:; BCL:0; PCL:0; RULEID:(22001); SRVR:AM5PR0802MB2610; nodisclaimer: True x-microsoft-antispam-prvs: x-exchange-antispam-report-test: UriScan:(250305191791016)(180628864354917)(22074186197030); x-exchange-antispam-report-cfa-test: BCL:0; PCL:0; RULEID:(6060326)(6040281)(601004)(2401047)(8121501046)(5005006)(3002001)(10201501046)(6055026)(6041223)(6061324); SRVR:AM5PR0802MB2610; BCL:0; PCL:0; RULEID:; SRVR:AM5PR0802MB2610; x-forefront-prvs: 01283822F8 x-forefront-antispam-report: SFV:NSPM; SFS:(10009020)(6009001)(7916002)(54534003)(199003)(189002)(377424004)(92566002)(2900100001)(8676002)(86362001)(4326007)(102836003)(101416001)(122556002)(106116001)(68736007)(106356001)(105586002)(66066001)(9686002)(50986999)(3846002)(2351001)(450100001)(33656002)(54356999)(6116002)(77096005)(2906002)(7846002)(2501003)(97736004)(7736002)(3660700001)(3280700002)(189998001)(5640700001)(6916009)(305945005)(4001150100001)(7696004)(8936002)(110136003)(76576001)(5660300001)(81166006)(6506003)(74316002)(87936001)(81156014)(41533002)(2004002); DIR:OUT; SFP:1101; SCL:1; SRVR:AM5PR0802MB2610; H:AM5PR0802MB2610.eurprd08.prod.outlook.com; FPR:; SPF:None; PTR:InfoNoRecords; A:1; MX:1; LANG:en; received-spf: None (protection.outlook.com: arm.com does not designate permitted sender hosts) spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM MIME-Version: 1.0 X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-originalarrivaltime: 16 Nov 2016 18:53:03.2104 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM5PR0802MB2610 Improve generic rawmemchr for targets that don't have an assembler version by tailcalling memchr with the maximum size. If a target has an optimized memchr this is significantly faster (~3x on AArch64), if not, then this makes little difference. Also optimize the special case of zero to use strlen as this is typically faster than memchr. ChangeLog: 2015-11-16 Wilco Dijkstra * string/rawmemchr.c (RAWMEMCHR): Use faster memchr/strlen. diff --git a/string/rawmemchr.c b/string/rawmemchr.c index fa3176d6ac7e25490be415af0459807509d1e02b..1a146af980619ac9a37a3c9d8df3917e7ce5db12 100644 --- a/string/rawmemchr.c +++ b/string/rawmemchr.c @@ -1,10 +1,5 @@ /* Copyright (C) 1991-2016 Free Software Foundation, Inc. This file is part of the GNU C Library. - Based on strlen implementation by Torbjorn Granlund (tege@sics.se), - with help from Dan Sahlin (dan@sics.se) and - commentary by Jim Blandy (jimb@ai.mit.edu); - adaptation to memchr suggested by Dick Karpinski (dick@cca.ucsf.edu), - and implemented by Roland McGrath (roland@ai.mit.edu). The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public @@ -20,157 +15,19 @@ License along with the GNU C Library; if not, see . */ -#ifdef HAVE_CONFIG_H -#include -#endif - -#undef __ptr_t -#define __ptr_t void * - -#if defined (_LIBC) -# include -# include -# include -#endif - -#if defined (HAVE_LIMITS_H) || defined (_LIBC) -# include -#endif - -#define LONG_MAX_32_BITS 2147483647 - -#ifndef LONG_MAX -#define LONG_MAX LONG_MAX_32_BITS -#endif - -#include - -#undef memchr +#include #ifndef RAWMEMCHR # define RAWMEMCHR __rawmemchr #endif /* Find the first occurrence of C in S. */ -__ptr_t -RAWMEMCHR (const __ptr_t s, int c_in) +void * +RAWMEMCHR (const void *s, int c) { - const unsigned char *char_ptr; - const unsigned long int *longword_ptr; - unsigned long int longword, magic_bits, charmask; - unsigned char c; - - c = (unsigned char) c_in; - - /* Handle the first few characters by reading one character at a time. - Do this until CHAR_PTR is aligned on a longword boundary. */ - for (char_ptr = (const unsigned char *) s; - ((unsigned long int) char_ptr & (sizeof (longword) - 1)) != 0; - ++char_ptr) - if (*char_ptr == c) - return (__ptr_t) char_ptr; - - /* All these elucidatory comments refer to 4-byte longwords, - but the theory applies equally well to 8-byte longwords. */ - - longword_ptr = (unsigned long int *) char_ptr; - - /* Bits 31, 24, 16, and 8 of this number are zero. Call these bits - the "holes." Note that there is a hole just to the left of - each byte, with an extra at the end: - - bits: 01111110 11111110 11111110 11111111 - bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD - - The 1-bits make sure that carries propagate to the next 0-bit. - The 0-bits provide holes for carries to fall into. */ - magic_bits = -1; - magic_bits = magic_bits / 0xff * 0xfe << 1 >> 1 | 1; - - /* Set up a longword, each of whose bytes is C. */ - charmask = c | (c << 8); - charmask |= charmask << 16; -#if LONG_MAX > LONG_MAX_32_BITS - charmask |= charmask << 32; -#endif - - /* Instead of the traditional loop which tests each character, - we will test a longword at a time. The tricky part is testing - if *any of the four* bytes in the longword in question are zero. */ - while (1) - { - /* We tentatively exit the loop if adding MAGIC_BITS to - LONGWORD fails to change any of the hole bits of LONGWORD. - - 1) Is this safe? Will it catch all the zero bytes? - Suppose there is a byte with all zeros. Any carry bits - propagating from its left will fall into the hole at its - least significant bit and stop. Since there will be no - carry from its most significant bit, the LSB of the - byte to the left will be unchanged, and the zero will be - detected. - - 2) Is this worthwhile? Will it ignore everything except - zero bytes? Suppose every byte of LONGWORD has a bit set - somewhere. There will be a carry into bit 8. If bit 8 - is set, this will carry into bit 16. If bit 8 is clear, - one of bits 9-15 must be set, so there will be a carry - into bit 16. Similarly, there will be a carry into bit - 24. If one of bits 24-30 is set, there will be a carry - into bit 31, so all of the hole bits will be changed. - - The one misfire occurs when bits 24-30 are clear and bit - 31 is set; in this case, the hole at bit 31 is not - changed. If we had access to the processor carry flag, - we could close this loophole by putting the fourth hole - at bit 32! - - So it ignores everything except 128's, when they're aligned - properly. - - 3) But wait! Aren't we looking for C, not zero? - Good point. So what we do is XOR LONGWORD with a longword, - each of whose bytes is C. This turns each byte that is C - into a zero. */ - - longword = *longword_ptr++ ^ charmask; - - /* Add MAGIC_BITS to LONGWORD. */ - if ((((longword + magic_bits) - - /* Set those bits that were unchanged by the addition. */ - ^ ~longword) - - /* Look at only the hole bits. If any of the hole bits - are unchanged, most likely one of the bytes was a - zero. */ - & ~magic_bits) != 0) - { - /* Which of the bytes was C? If none of them were, it was - a misfire; continue the search. */ - - const unsigned char *cp = (const unsigned char *) (longword_ptr - 1); - - if (cp[0] == c) - return (__ptr_t) cp; - if (cp[1] == c) - return (__ptr_t) &cp[1]; - if (cp[2] == c) - return (__ptr_t) &cp[2]; - if (cp[3] == c) - return (__ptr_t) &cp[3]; -#if LONG_MAX > 2147483647 - if (cp[4] == c) - return (__ptr_t) &cp[4]; - if (cp[5] == c) - return (__ptr_t) &cp[5]; - if (cp[6] == c) - return (__ptr_t) &cp[6]; - if (cp[7] == c) - return (__ptr_t) &cp[7]; -#endif - } - } + if (c != '\0') + return memchr (s, c, (size_t)-1); + return (char *)s + strlen (s); } libc_hidden_def (__rawmemchr) weak_alias (__rawmemchr, rawmemchr)