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72 lines
2.1 KiB
C
72 lines
2.1 KiB
C
/* Copyright (C) 1991-2023 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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This program 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
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License along
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with this program; if not, write to the Free Software Foundation,
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Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
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/*
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@deftypefn Supplemental void* memmem (const void *@var{haystack}, @
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size_t @var{haystack_len} const void *@var{needle}, size_t @var{needle_len})
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Returns a pointer to the first occurrence of @var{needle} (length
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@var{needle_len}) in @var{haystack} (length @var{haystack_len}).
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Returns @code{NULL} if not found.
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@end deftypefn
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*/
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#ifndef _LIBC
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# include <config.h>
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#endif
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#include <stddef.h>
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#include <string.h>
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#ifndef _LIBC
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# define __builtin_expect(expr, val) (expr)
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#endif
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#undef memmem
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/* Return the first occurrence of NEEDLE in HAYSTACK. */
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void *
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memmem (const void *haystack, size_t haystack_len, const void *needle,
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size_t needle_len)
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{
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const char *begin;
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const char *const last_possible
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= (const char *) haystack + haystack_len - needle_len;
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if (needle_len == 0)
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/* The first occurrence of the empty string is deemed to occur at
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the beginning of the string. */
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return (void *) haystack;
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/* Sanity check, otherwise the loop might search through the whole
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memory. */
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if (__builtin_expect (haystack_len < needle_len, 0))
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return NULL;
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for (begin = (const char *) haystack; begin <= last_possible; ++begin)
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if (begin[0] == ((const char *) needle)[0] &&
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!memcmp ((const void *) &begin[1],
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(const void *) ((const char *) needle + 1),
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needle_len - 1))
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return (void *) begin;
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return NULL;
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}
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