From patchwork Wed May 27 09:18:58 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ondrej Bilka X-Patchwork-Id: 6937 Received: (qmail 526 invoked by alias); 27 May 2015 09:19:21 -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 475 invoked by uid 89); 27 May 2015 09:19:20 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=1.3 required=5.0 tests=AWL, BAYES_80, FREEMAIL_FROM, SPF_NEUTRAL autolearn=no version=3.3.2 X-HELO: popelka.ms.mff.cuni.cz Date: Wed, 27 May 2015 11:18:58 +0200 From: =?utf-8?B?T25kxZllaiBCw61sa2E=?= To: libc-alpha@sourceware.org Subject: [PATCH 3/* v2] Generic string strlen and rawmemchr Message-ID: <20150527091858.GC27814@domone> References: <20150527060121.GA19105@domone> <20150527090717.GA27814@domone> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20150527090717.GA27814@domone> User-Agent: Mutt/1.5.20 (2009-06-14) With strlen and rawmemchr I use same idea. As one could get rawmemchr with strlen by first xoring input and strlen from rawmemchr by letting gcc optimize rawmemchr(x,0) these belong together. I keep them separate now but it could change if you want it. * string/strlen.c: Use skeleton. * string/rawmemchr.c: Likewise. diff --git a/string/rawmemchr.c b/string/rawmemchr.c index 05b22be..4aeaf03 100644 --- a/string/rawmemchr.c +++ b/string/rawmemchr.c @@ -1,10 +1,5 @@ /* Copyright (C) 1991-2015 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 @@ -20,166 +15,23 @@ License along with the GNU C Library; if not, see . */ -#ifdef HAVE_CONFIG_H -#include -#endif +#include +#include -#undef __ptr_t -#define __ptr_t void * +#undef rawmemchr +#undef __rawmemchr -#if defined (_LIBC) -# include -# include -# include -#endif -#if defined (HAVE_LIMITS_H) || defined (_LIBC) -# include -#endif +#include "string/common.h" +#define EXPRESSION(p, c) (contains_zero (p ^ c)) +#include "string/skeleton.h" -#define LONG_MAX_32_BITS 2147483647 - -#ifndef LONG_MAX -#define LONG_MAX LONG_MAX_32_BITS -#endif - -#include - -#undef memchr - -#ifndef RAWMEMCHR -# define RAWMEMCHR __rawmemchr -#endif - -/* Find the first occurrence of C in S. */ -__ptr_t -RAWMEMCHR (s, c_in) - 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. */ - - if (sizeof (longword) != 4 && sizeof (longword) != 8) - abort (); - -#if LONG_MAX <= LONG_MAX_32_BITS - magic_bits = 0x7efefeff; -#else - magic_bits = ((unsigned long int) 0x7efefefe << 32) | 0xfefefeff; -#endif - - /* 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 - } - } + return (void *) string_skeleton (s, c, NULL); } + libc_hidden_def (__rawmemchr) weak_alias (__rawmemchr, rawmemchr) + diff --git a/string/strlen.c b/string/strlen.c index d066bde..2cc0369 100644 --- a/string/strlen.c +++ b/string/strlen.c @@ -1,8 +1,5 @@ /* Copyright (C) 1991-2015 Free Software Foundation, Inc. This file is part of the GNU C Library. - Written by Torbjorn Granlund (tege@sics.se), - with help from Dan Sahlin (dan@sics.se); - commentary by Jim Blandy (jimb@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 @@ -25,81 +22,15 @@ /* Return the length of the null-terminated string STR. Scan for the null terminator quickly by testing four bytes at a time. */ + +#include "string/common.h" +#define EXPRESSION(p, c) (contains_zero (p)) +#include "string/skeleton.h" + size_t strlen (const char *str) { - const char *char_ptr; - const unsigned long int *longword_ptr; - unsigned long int longword, himagic, lomagic; - - /* 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 = str; ((unsigned long int) char_ptr - & (sizeof (longword) - 1)) != 0; - ++char_ptr) - if (*char_ptr == '\0') - return char_ptr - str; - - /* 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. */ - himagic = 0x80808080L; - lomagic = 0x01010101L; - if (sizeof (longword) > 4) - { - /* 64-bit version of the magic. */ - /* Do the shift in two steps to avoid a warning if long has 32 bits. */ - himagic = ((himagic << 16) << 16) | himagic; - lomagic = ((lomagic << 16) << 16) | lomagic; - } - if (sizeof (longword) > 8) - abort (); - - /* 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. */ - for (;;) - { - longword = *longword_ptr++; - - if (((longword - lomagic) & ~longword & himagic) != 0) - { - /* Which of the bytes was the zero? If none of them were, it was - a misfire; continue the search. */ - - const char *cp = (const char *) (longword_ptr - 1); - - if (cp[0] == 0) - return cp - str; - if (cp[1] == 0) - return cp - str + 1; - if (cp[2] == 0) - return cp - str + 2; - if (cp[3] == 0) - return cp - str + 3; - if (sizeof (longword) > 4) - { - if (cp[4] == 0) - return cp - str + 4; - if (cp[5] == 0) - return cp - str + 5; - if (cp[6] == 0) - return cp - str + 6; - if (cp[7] == 0) - return cp - str + 7; - } - } - } + return string_skeleton (str, 0, 0) - str; } + libc_hidden_builtin_def (strlen)