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.

4 files changed, 176 insertions, 0 deletions

diff --git a/share/man/man9/memcchr.3 b/share/man/man9/memcchr.3
new file mode 100644
index 0000000..a3ade21
--- /dev/null
+++ b/share/man/man9/memcchr.3
@@ -0,0 +1,59 @@
+.\" Copyright (c) 2012 Ed Schouten <ed@FreeBSD.org>
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd January 1, 2012
+.Dt MEMCCHR 9
+.Os
+.Sh NAME
+.Nm memcchr
+.Nd locate the complement of a byte in byte string
+.Sh SYNOPSIS
+.In sys/libkern.h
+.Ft void *
+.Fn memcchr "const void *b" "int c" "size_t len"
+.Sh DESCRIPTION
+The
+.Fn memcchr
+function locates the first occurrence of a byte unequal to
+.Fa c
+(converted to an
+.Vt "unsigned char" )
+in string
+.Fa b .
+.Sh RETURN VALUES
+The
+.Fn memcchr
+function return a pointer to the byte located, or NULL if no such byte
+exists within
+.Fa len
+bytes.
+.Sh SEE ALSO
+.Xr memchr 3
+.Sh HISTORY
+The
+.Fn memcchr
+function first appeared in
+.Fx 10.0 .
diff --git a/sys/conf/files b/sys/conf/files
index 2f8b5f6..871921c 100644
--- a/sys/conf/files
+++ b/sys/conf/files
@@ -2557,6 +2557,7 @@ libkern/inet_ntoa.c		standard
 libkern/inet_ntop.c		standard
 libkern/inet_pton.c		standard
 libkern/mcount.c		optional profiling-routine
+libkern/memcchr.c		standard
 libkern/memcmp.c		standard
 libkern/qsort.c			standard
 libkern/qsort_r.c		standard
diff --git a/sys/libkern/memcchr.c b/sys/libkern/memcchr.c
new file mode 100644
index 0000000..eebb23a
--- /dev/null
+++ b/sys/libkern/memcchr.c
@@ -0,0 +1,115 @@
+/*-
+ * Copyright (c) 2012 Ed Schouten <ed@FreeBSD.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/libkern.h>
+#include <sys/limits.h>
+#include <sys/param.h>
+
+/*
+ * memcchr(): find first character in buffer not matching `c'.
+ *
+ * This function performs the complement of memchr().  To provide decent
+ * performance, this function compares data from the buffer one word at
+ * a time.
+ *
+ * This code is inspired by libc's strlen(), written by Xin Li.
+ */
+
+#if LONG_BIT != 32 && LONG_BIT != 64
+#error Unsupported word size
+#endif
+
+#define	LONGPTR_MASK (sizeof(long) - 1)
+
+#define	TESTBYTE				\
+	do {					\
+		if (*p != (unsigned char)c)	\
+			goto done;		\
+		p++;				\
+	} while (0)
+
+void *
+memcchr(const void *begin, int c, size_t n)
+{
+	const unsigned long *lp;
+	const unsigned char *p, *end;
+	unsigned long word;
+
+	/* Four or eight repetitions of `c'. */
+	word = (unsigned char)c;
+	word |= word << 8;
+	word |= word << 16;
+#if LONG_BIT >= 64
+	word |= word << 32;
+#endif
+
+	/* Don't perform memory I/O when passing a zero-length buffer. */
+	if (n == 0)
+		return (NULL);
+
+	/*
+	 * First determine whether there is a character unequal to `c'
+	 * in the first word.  As this word may contain bytes before
+	 * `begin', we may execute this loop spuriously.
+	 */
+	lp = (const unsigned long *)((uintptr_t)begin & ~LONGPTR_MASK);
+	end = (const unsigned char *)begin + n;
+	if (*lp++ != word)
+		for (p = begin; p < (const unsigned char *)lp;)
+			TESTBYTE;
+
+	/* Now compare the data one word at a time. */
+	for (; (const unsigned char *)lp < end; lp++) {
+		if (*lp != word) {
+			p = (const unsigned char *)lp;
+			TESTBYTE;
+			TESTBYTE;
+			TESTBYTE;
+#if LONG_BIT >= 64
+			TESTBYTE;
+			TESTBYTE;
+			TESTBYTE;
+			TESTBYTE;
+#endif
+			goto done;
+		}
+	}
+
+	return (NULL);
+
+done:
+	/*
+	 * If the end of the buffer is not word aligned, the previous
+	 * loops may obtain an address that's beyond the end of the
+	 * buffer.
+	 */
+	if (p < end)
+		return (__DECONST(void *, p));
+	return (NULL);
+}
diff --git a/sys/sys/libkern.h b/sys/sys/libkern.h
index aa53fb7..0e525de 100644
--- a/sys/sys/libkern.h
+++ b/sys/sys/libkern.h
@@ -92,6 +92,7 @@ int	 flsl(long);
 int	 fnmatch(const char *, const char *, int);
 int	 locc(int, char *, u_int);
 void	*memchr(const void *s, int c, size_t n);
+void	*memcchr(const void *s, int c, size_t n);
 int	 memcmp(const void *b1, const void *b2, size_t len);
 void	 qsort(void *base, size_t nmemb, size_t size,
 	    int (*compar)(const void *, const void *));