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58 lines
1.9 KiB
C
58 lines
1.9 KiB
C
/* Copyright (C) 2013-2017 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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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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#include <stdint.h>
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#include "string-endian.h"
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/* Find the length of S, but scan at most MAXLEN characters. If no
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'\0' terminator is found in that many characters, return MAXLEN. */
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size_t
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__strnlen (const char *s, size_t maxlen)
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{
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/* When maxlen is 0, can't read any bytes or it might cause a page fault. */
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if (maxlen == 0)
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return 0;
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/* Get an aligned pointer. */
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const uintptr_t s_int = (uintptr_t) s;
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const uint64_t *p = (const uint64_t *) (s_int & -8);
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size_t bytes_read = sizeof (*p) - (s_int & (sizeof (*p) - 1));
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/* Read and MASK the first word. */
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uint64_t v = *p | MASK (s_int);
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uint64_t bits;
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while ((bits = __insn_v1cmpeqi (v, 0)) == 0)
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{
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if (bytes_read >= maxlen)
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{
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/* Read maxlen bytes and didn't find the terminator. */
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return maxlen;
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}
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v = *++p;
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bytes_read += sizeof (v);
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}
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/* Found '\0', check it is not larger than maxlen */
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size_t len = ((const char *) p) + (CFZ (bits) >> 3) - s;
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return (len < maxlen ? len : maxlen);
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}
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libc_hidden_def (__strnlen)
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weak_alias (__strnlen, strnlen)
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libc_hidden_def (strnlen)
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