From patchwork Sat Dec 17 06:57:24 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Richard Henderson X-Patchwork-Id: 706652 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from sourceware.org (server1.sourceware.org [209.132.180.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 3tgdLg1KbPz9t2D for ; Sat, 17 Dec 2016 17:58:34 +1100 (AEDT) Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; secure) header.d=sourceware.org header.i=@sourceware.org header.b="B+F8uTsK"; dkim-atps=neutral DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:from:to:subject:date:message-id:in-reply-to :references; q=dns; s=default; b=PHZ6IslXYd1eVFbEOoMc/rQv0TXSR0e 3DdozjRuzDVEgV44nbSRR4r7ZuxZ+jngCT4lhHnx2MEtJdnaJgTIpT4opoWEpNfN D3EMNLKIPRVvL6KHQG24RNYEJf4bqr5nN8XR3tmP3OHhiNsEqKiXUE9zoVNDExaB 8H8We1o/ZrSk= DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:from:to:subject:date:message-id:in-reply-to :references; s=default; bh=pqcXWtLuusTctFXiW2aTUSk/91M=; b=B+F8u TsKVezpRRlyyXmy48zkpXyCUp+XsO2Jit4GWwj8Hedq2VEaa+FGddrtcynyYUXHR 3/r2SE0eAOvQ/9iqx4prZsGhyfi4yxkYbR98boWyp8Eu7V97R1zvUHxGPm86myeQ ZJBFldumUC1NfkubuTiBI2kFzQxZ5OHSikPWL8= Received: (qmail 93224 invoked by alias); 17 Dec 2016 06:57:53 -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 92932 invoked by uid 89); 17 Dec 2016 06:57:51 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.1 required=5.0 tests=BAYES_00, FREEMAIL_ENVFROM_END_DIGIT, FREEMAIL_FROM, RCVD_IN_DNSWL_NONE, RCVD_IN_SORBS_SPAM, SPF_PASS autolearn=no version=3.3.2 spammy=H*RU:74.125.83.65, Hx-spam-relays-external:74.125.83.65, holes, our X-HELO: mail-pg0-f65.google.com X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:from:to:subject:date:message-id :in-reply-to:references; bh=Y2yHalUU18anNbXWS8RzcZdH2VzDmPucNPF7FyOY1zg=; b=tYfkiK9MGv3wItGoMpjBWItN+oiMDeQet20GqXj9+E2vfkt6uEm79msa692rPq5k3z dB37LHUGUSowa6CgZbvT7WnRdxVdXwuk6pewBQnH5tlYzs2Dlq+oyFD3Kf+S/A2sWUri YFGol4FSyhsv709THaBkg57N6xuY1VRa1czJFdHy5Dqe7f/ZLHfCAFtYhY6Jynlchioa Sjlq5kvrlujI8PfgMw9CflnRvSmBdpsUMsqPUXqnm+59kTTpGq8gyDs6fuYAd/0HRIi7 632qRs5VwbeuO48PGH4r8hGJYbWftndWvu6shzFU3iIlRAtQ5jN5F2ngUqPm3ogK6UIw cEAQ== X-Gm-Message-State: AKaTC02WkO2chsTwuPpycDRUFsHEKl4oEDtt8fxHJUem0BsF6Yc6STMD3ic7DoXn2vKWYg== X-Received: by 10.84.218.13 with SMTP id q13mr14997820pli.168.1481957863271; Fri, 16 Dec 2016 22:57:43 -0800 (PST) From: Richard Henderson To: libc-alpha@sourceware.org Subject: [PATCH 06/11] Improve generic memrchr Date: Fri, 16 Dec 2016 22:57:24 -0800 Message-Id: <20161217065729.28561-7-rth@twiddle.net> In-Reply-To: <20161217065729.28561-1-rth@twiddle.net> References: <20161217065729.28561-1-rth@twiddle.net> * string/memrchr.c: Use haszero.h, whichzero.h. --- string/memrchr.c | 180 ++++++++++--------------------------------------------- 1 file changed, 30 insertions(+), 150 deletions(-) diff --git a/string/memrchr.c b/string/memrchr.c index b9b0c9e..d45b261 100644 --- a/string/memrchr.c +++ b/string/memrchr.c @@ -21,180 +21,60 @@ License along with the GNU C Library; if not, see . */ -#include - -#ifdef HAVE_CONFIG_H -# include -#endif - -#undef __ptr_t -#define __ptr_t void * - -#if defined _LIBC -# 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 +#include +#include +#include +#include #undef __memrchr #undef memrchr -#ifndef weak_alias -# define __memrchr memrchr -#endif - /* Search no more than N bytes of S for C. */ -__ptr_t -#ifndef MEMRCHR -__memrchr -#else -MEMRCHR -#endif - (const __ptr_t s, int c_in, size_t n) +void * +__memrchr (const void *s, int c_in, size_t n) { - const unsigned char *char_ptr; + const unsigned char *char_ptr = (const unsigned char *) s + n; const unsigned long int *longword_ptr; - unsigned long int longword, magic_bits, charmask; + unsigned long int longword, repeated_c; + uintptr_t i, align; unsigned char c; c = (unsigned char) c_in; /* Handle the last 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 + n; - n > 0 && ((unsigned long int) char_ptr - & (sizeof (longword) - 1)) != 0; - --n) + align = (uintptr_t)char_ptr % sizeof(longword); + for (i = 0; i < align; ++i) if (*--char_ptr == c) - return (__ptr_t) char_ptr; + return (void *) char_ptr; - /* All these elucidatory comments refer to 4-byte longwords, - but the theory applies equally well to 8-byte longwords. */ + /* Set up a longword, each of whose bytes is C. */ + repeated_c = (-1ul / 0xff) * c; longword_ptr = (const unsigned long int *) char_ptr; + n -= align; + if (__glibc_unlikely(n == 0)) + return NULL; - /* 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 (n >= sizeof (longword)) + /* Loop while we have more than one longword remaining. */ + while (n > sizeof (longword)) { - /* 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; - -#if LONG_MAX > 2147483647 - if (cp[7] == c) - return (__ptr_t) &cp[7]; - if (cp[6] == c) - return (__ptr_t) &cp[6]; - if (cp[5] == c) - return (__ptr_t) &cp[5]; - if (cp[4] == c) - return (__ptr_t) &cp[4]; -#endif - if (cp[3] == c) - return (__ptr_t) &cp[3]; - if (cp[2] == c) - return (__ptr_t) &cp[2]; - if (cp[1] == c) - return (__ptr_t) &cp[1]; - if (cp[0] == c) - return (__ptr_t) cp; - } - + longword = *--longword_ptr ^ repeated_c; + if (haszero (longword)) + goto found; n -= sizeof (longword); } - char_ptr = (const unsigned char *) longword_ptr; - - while (n-- > 0) + /* Since our pointer is aligned, we can always read the last longword. */ + longword = *--longword_ptr ^ repeated_c; + if (haszero (longword)) { - if (*--char_ptr == c) - return (__ptr_t) char_ptr; + found: + i = whichzero (longword); + if (sizeof (longword) - 1 - i < n) + return (char *) longword_ptr + i; } - return 0; + return NULL; } -#ifndef MEMRCHR -# ifdef weak_alias weak_alias (__memrchr, memrchr) -# endif -#endif