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f18b8dc7d7
Avoid an issue in gcc where some of the vector (aka SIMD) ops will sometimes end up getting wrongly optimized out. We use these instructions in many of the string implementations. If/when we have an upstreamed fix for this problem in gcc we can conditionalize the use of the extended assembly workaround in glibc.
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 = 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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