Introducing memcchr(3).
It seems two of the file system drivers we have in the tree, namely ufs and ext3, use a function called `skpc()'. The meaning of this function does not seem to be documented in FreeBSD, but it turns out one needs to be a VAX programmer to understand what it does. SPKC is an instruction on the VAX that does the opposite of memchr(). It searches for the non-equal character. Add a new function called memcchr() to the tree that has the following advantages over skpc(): - It has a name that makes more sense than skpc(). Just like strcspn() matches the complement of strspn(), memcchr() is the complement of memchr(). - It is faster than skpc(). Similar to our strlen() in libc, it compares entire words, instead of single bytes. It seems that for this routine this yields a sixfold performance increase on amd64. - It has a man page.
This commit is contained in:
Ed Schouten
parent
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commit
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=229198
59
share/man/man9/memcchr.3
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59
share/man/man9/memcchr.3
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@ -0,0 +1,59 @@
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.\" Copyright (c) 2012 Ed Schouten <ed@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd January 1, 2012
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.Dt MEMCCHR 9
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.Os
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.Sh NAME
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.Nm memcchr
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.Nd locate the complement of a byte in byte string
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.Sh SYNOPSIS
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.In sys/libkern.h
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.Ft void *
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.Fn memcchr "const void *b" "int c" "size_t len"
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.Sh DESCRIPTION
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The
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.Fn memcchr
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function locates the first occurrence of a byte unequal to
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.Fa c
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(converted to an
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.Vt "unsigned char" )
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in string
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.Fa b .
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.Sh RETURN VALUES
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The
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.Fn memcchr
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function return a pointer to the byte located, or NULL if no such byte
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exists within
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.Fa len
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bytes.
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.Sh SEE ALSO
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.Xr memchr 3
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.Sh HISTORY
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The
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.Fn memcchr
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function first appeared in
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.Fx 10.0 .
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@ -2557,6 +2557,7 @@ libkern/inet_ntoa.c standard
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libkern/inet_ntop.c standard
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libkern/inet_pton.c standard
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libkern/mcount.c optional profiling-routine
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libkern/memcchr.c standard
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libkern/memcmp.c standard
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libkern/qsort.c standard
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libkern/qsort_r.c standard
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115
sys/libkern/memcchr.c
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115
sys/libkern/memcchr.c
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@ -0,0 +1,115 @@
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/*-
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* Copyright (c) 2012 Ed Schouten <ed@FreeBSD.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/libkern.h>
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#include <sys/limits.h>
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#include <sys/param.h>
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/*
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* memcchr(): find first character in buffer not matching `c'.
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*
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* This function performs the complement of memchr(). To provide decent
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* performance, this function compares data from the buffer one word at
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* a time.
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*
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* This code is inspired by libc's strlen(), written by Xin Li.
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*/
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#if LONG_BIT != 32 && LONG_BIT != 64
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#error Unsupported word size
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#endif
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#define LONGPTR_MASK (sizeof(long) - 1)
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#define TESTBYTE \
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do { \
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if (*p != (unsigned char)c) \
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goto done; \
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p++; \
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} while (0)
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void *
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memcchr(const void *begin, int c, size_t n)
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{
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const unsigned long *lp;
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const unsigned char *p, *end;
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unsigned long word;
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/* Four or eight repetitions of `c'. */
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word = (unsigned char)c;
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word |= word << 8;
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word |= word << 16;
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#if LONG_BIT >= 64
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word |= word << 32;
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#endif
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/* Don't perform memory I/O when passing a zero-length buffer. */
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if (n == 0)
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return (NULL);
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/*
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* First determine whether there is a character unequal to `c'
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* in the first word. As this word may contain bytes before
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* `begin', we may execute this loop spuriously.
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*/
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lp = (const unsigned long *)((uintptr_t)begin & ~LONGPTR_MASK);
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end = (const unsigned char *)begin + n;
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if (*lp++ != word)
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for (p = begin; p < (const unsigned char *)lp;)
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TESTBYTE;
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/* Now compare the data one word at a time. */
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for (; (const unsigned char *)lp < end; lp++) {
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if (*lp != word) {
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p = (const unsigned char *)lp;
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TESTBYTE;
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TESTBYTE;
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TESTBYTE;
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#if LONG_BIT >= 64
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TESTBYTE;
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TESTBYTE;
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TESTBYTE;
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TESTBYTE;
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#endif
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goto done;
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}
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}
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return (NULL);
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done:
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/*
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* If the end of the buffer is not word aligned, the previous
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* loops may obtain an address that's beyond the end of the
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* buffer.
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*/
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if (p < end)
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return (__DECONST(void *, p));
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return (NULL);
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}
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@ -92,6 +92,7 @@ int flsl(long);
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int fnmatch(const char *, const char *, int);
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int locc(int, char *, u_int);
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void *memchr(const void *s, int c, size_t n);
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void *memcchr(const void *s, int c, size_t n);
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int memcmp(const void *b1, const void *b2, size_t len);
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void qsort(void *base, size_t nmemb, size_t size,
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int (*compar)(const void *, const void *));
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