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de85bfc508
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.
116 lines
3.2 KiB
C
116 lines
3.2 KiB
C
/*-
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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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