Blame sysdeps/i386/strlen.c

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/* Determine the length of a string.  For Intel 80x86, x>=3.
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   Copyright (C) 1991-2018 Free Software Foundation, Inc.
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   This file is part of the GNU C Library.
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   Contributed by Torbjorn Granlund (tege@sics.se).
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   The GNU C Library is free software; you can redistribute it and/or
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   modify it under the terms of the GNU Lesser General Public
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   License as published by the Free Software Foundation; either
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   version 2.1 of the License, or (at your option) any later version.
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   The GNU C Library is distributed in the hope that it will be useful,
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   but WITHOUT ANY WARRANTY; without even the implied warranty of
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   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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   Lesser General Public License for more details.
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   You should have received a copy of the GNU Lesser General Public
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   License along with the GNU C Library; if not, see
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   <http://www.gnu.org/licenses/>.  */
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#include <string.h>
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size_t
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strlen (const char *str)
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{
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  int cnt;
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  asm("cld\n"			/* Search forward.  */
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      /* Some old versions of gas need `repne' instead of `repnz'.  */
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      "repnz\n"			/* Look for a zero byte.  */
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      "scasb" /* %0, %1, %3 */ :
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      "=c" (cnt) : "D" (str), "0" (-1), "a" (0));
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  return -2 - cnt;
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}
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libc_hidden_builtin_def (strlen)