From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 1791) id D777F3858418; Mon, 6 Feb 2023 20:14:01 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org D777F3858418 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1675714441; bh=blYeJLK7dZprkCcdEhVmIFI9rlUtldaXvw0S3dF7lW8=; h=From:To:Subject:Date:From; b=X8w8XLEXTJih1fYew3ZlljA4iPSlSqabbaKmeCBEYtkG3QIbqGI4sEQk7hXI31Ku2 xpNHeKYkwxmGaNXdalW5ZLdsf92fK3JmYXgDMrtjCBVTcQluJnk2rWVAhEht1dxE+b biXh/ejED75w8kl/7pwY0RnodKY5tXA6+ErTtEPI= Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit From: Adhemerval Zanella To: glibc-cvs@sourceware.org Subject: [glibc] string: Improve generic strnlen with memchr X-Act-Checkin: glibc X-Git-Author: Adhemerval Zanella X-Git-Refname: refs/heads/master X-Git-Oldrev: 2a8867a17ffe5c5a4251fd40bf6c73a3fd426062 X-Git-Newrev: 0f4254311ebf15b8f3f6f66182e8dd5151a58a88 Message-Id: <20230206201401.D777F3858418@sourceware.org> Date: Mon, 6 Feb 2023 20:14:01 +0000 (GMT) List-Id: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=0f4254311ebf15b8f3f6f66182e8dd5151a58a88 commit 0f4254311ebf15b8f3f6f66182e8dd5151a58a88 Author: Adhemerval Zanella Date: Tue Jan 10 18:00:55 2023 -0300 string: Improve generic strnlen with memchr It also cleanups the multiple inclusion by leaving the ifunc implementation to undef the weak_alias and libc_hidden_def. Co-authored-by: Richard Henderson Reviewed-by: Noah Goldstein Diff: --- string/strnlen.c | 137 +-------------------- sysdeps/i386/i686/multiarch/strnlen-c.c | 14 +-- .../powerpc32/power4/multiarch/strnlen-ppc32.c | 14 +-- sysdeps/s390/strnlen-c.c | 14 ++- 4 files changed, 27 insertions(+), 152 deletions(-) diff --git a/string/strnlen.c b/string/strnlen.c index 6ff294eab1..dc23354ec8 100644 --- a/string/strnlen.c +++ b/string/strnlen.c @@ -1,10 +1,6 @@ /* Find the length of STRING, but scan at most MAXLEN characters. Copyright (C) 1991-2023 Free Software Foundation, Inc. - Based on strlen 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 License as published by the Free Software Foundation; either version 2.1 of the @@ -20,7 +16,6 @@ not, see . */ #include -#include /* Find the length of S, but scan at most MAXLEN characters. If no '\0' terminator is found in that many characters, return MAXLEN. */ @@ -32,134 +27,12 @@ size_t __strnlen (const char *str, size_t maxlen) { - const char *char_ptr, *end_ptr = str + maxlen; - const unsigned long int *longword_ptr; - unsigned long int longword, himagic, lomagic; - - if (maxlen == 0) - return 0; - - if (__glibc_unlikely (end_ptr < str)) - end_ptr = (const char *) ~0UL; - - /* 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') - { - if (char_ptr > end_ptr) - char_ptr = end_ptr; - 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. */ - while (longword_ptr < (unsigned long int *) end_ptr) - { - /* 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. */ - - longword = *longword_ptr++; - - if ((longword - lomagic) & himagic) - { - /* 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); - - char_ptr = cp; - if (cp[0] == 0) - break; - char_ptr = cp + 1; - if (cp[1] == 0) - break; - char_ptr = cp + 2; - if (cp[2] == 0) - break; - char_ptr = cp + 3; - if (cp[3] == 0) - break; - if (sizeof (longword) > 4) - { - char_ptr = cp + 4; - if (cp[4] == 0) - break; - char_ptr = cp + 5; - if (cp[5] == 0) - break; - char_ptr = cp + 6; - if (cp[6] == 0) - break; - char_ptr = cp + 7; - if (cp[7] == 0) - break; - } - } - char_ptr = end_ptr; - } - - if (char_ptr > end_ptr) - char_ptr = end_ptr; - return char_ptr - str; + const char *found = memchr (str, '\0', maxlen); + return found ? found - str : maxlen; } + #ifndef STRNLEN -libc_hidden_def (__strnlen) weak_alias (__strnlen, strnlen) -#endif +libc_hidden_def (__strnlen) libc_hidden_def (strnlen) +#endif diff --git a/sysdeps/i386/i686/multiarch/strnlen-c.c b/sysdeps/i386/i686/multiarch/strnlen-c.c index 351e939a93..beb0350d53 100644 --- a/sysdeps/i386/i686/multiarch/strnlen-c.c +++ b/sysdeps/i386/i686/multiarch/strnlen-c.c @@ -1,10 +1,10 @@ #define STRNLEN __strnlen_ia32 +#include + #ifdef SHARED -# undef libc_hidden_def -# define libc_hidden_def(name) \ - __hidden_ver1 (__strnlen_ia32, __GI_strnlen, __strnlen_ia32); \ - strong_alias (__strnlen_ia32, __strnlen_ia32_1); \ - __hidden_ver1 (__strnlen_ia32_1, __GI___strnlen, __strnlen_ia32_1); +/* Alias for internal symbol to avoid PLT generation, it redirects the + libc_hidden_def (__strnlen/strlen) to default implementation. */ +__hidden_ver1 (__strnlen_ia32, __GI_strnlen, __strnlen_ia32); +strong_alias (__strnlen_ia32, __strnlen_ia32_1); +__hidden_ver1 (__strnlen_ia32_1, __GI___strnlen, __strnlen_ia32_1); #endif - -#include "string/strnlen.c" diff --git a/sysdeps/powerpc/powerpc32/power4/multiarch/strnlen-ppc32.c b/sysdeps/powerpc/powerpc32/power4/multiarch/strnlen-ppc32.c index 957b9b99e8..2ca1cd7181 100644 --- a/sysdeps/powerpc/powerpc32/power4/multiarch/strnlen-ppc32.c +++ b/sysdeps/powerpc/powerpc32/power4/multiarch/strnlen-ppc32.c @@ -17,12 +17,12 @@ . */ #define STRNLEN __strnlen_ppc +#include + #ifdef SHARED -# undef libc_hidden_def -# define libc_hidden_def(name) \ - __hidden_ver1 (__strnlen_ppc, __GI_strnlen, __strnlen_ppc); \ - strong_alias (__strnlen_ppc, __strnlen_ppc_1); \ - __hidden_ver1 (__strnlen_ppc_1, __GI___strnlen, __strnlen_ppc_1); +/* Alias for internal symbol to avoid PLT generation, it redirects the + libc_hidden_def (__strnlen/strlen) to default implementation. */ +__hidden_ver1 (__strnlen_ppc, __GI_strnlen, __strnlen_ppc); \ +strong_alias (__strnlen_ppc, __strnlen_ppc_1); \ +__hidden_ver1 (__strnlen_ppc_1, __GI___strnlen, __strnlen_ppc_1); #endif - -#include diff --git a/sysdeps/s390/strnlen-c.c b/sysdeps/s390/strnlen-c.c index 172fcc7caa..95156a0ff5 100644 --- a/sysdeps/s390/strnlen-c.c +++ b/sysdeps/s390/strnlen-c.c @@ -21,14 +21,16 @@ #if HAVE_STRNLEN_C # if HAVE_STRNLEN_IFUNC # define STRNLEN STRNLEN_C +# endif + +# include + +# if HAVE_STRNLEN_IFUNC # if defined SHARED && IS_IN (libc) -# undef libc_hidden_def -# define libc_hidden_def(name) \ - __hidden_ver1 (__strnlen_c, __GI_strnlen, __strnlen_c); \ - strong_alias (__strnlen_c, __strnlen_c_1); \ - __hidden_ver1 (__strnlen_c_1, __GI___strnlen, __strnlen_c_1); +__hidden_ver1 (__strnlen_c, __GI_strnlen, __strnlen_c); +strong_alias (__strnlen_c, __strnlen_c_1); +__hidden_ver1 (__strnlen_c_1, __GI___strnlen, __strnlen_c_1); # endif # endif -# include #endif