Initial Spring 2016 commit.

common/libc/string/memmove.c

@@ -0,0 +1,117 @@
+/*
+ * Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
+ *	The President and Fellows of Harvard College.
+ *
+ * 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.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY 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 UNIVERSITY 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.
+ */
+
+/*
+ * This file is shared between libc and the kernel, so don't put anything
+ * in here that won't work in both contexts.
+ */
+
+#ifdef _KERNEL
+#include <types.h>
+#include <lib.h>
+#else
+#include <stdint.h>
+#include <string.h>
+#endif
+
+/*
+ * C standard function - copy a block of memory, handling overlapping
+ * regions correctly.
+ */
+
+void *
+memmove(void *dst, const void *src, size_t len)
+{
+	size_t i;
+
+	/*
+	 * If the buffers don't overlap, it doesn't matter what direction
+	 * we copy in. If they do, it does, so just assume they always do.
+	 * We don't concern ourselves with the possibility that the region
+	 * to copy might roll over across the top of memory, because it's
+	 * not going to happen.
+	 *
+	 * If the destination is above the source, we have to copy
+	 * back to front to avoid overwriting the data we want to
+	 * copy.
+	 *
+	 *      dest:       dddddddd
+	 *      src:    ssssssss   ^
+	 *              |   ^  |___|
+         *              |___|
+	 *
+	 * If the destination is below the source, we have to copy
+	 * front to back.
+	 *
+	 *      dest:   dddddddd
+	 *      src:    ^   ssssssss
+	 *              |___|  ^   |
+         *                     |___|
+	 */
+
+	if ((uintptr_t)dst < (uintptr_t)src) {
+		/*
+		 * As author/maintainer of libc, take advantage of the
+		 * fact that we know memcpy copies forwards.
+		 */
+		return memcpy(dst, src, len);
+	}
+
+	/*
+	 * Copy by words in the common case. Look in memcpy.c for more
+	 * information.
+	 */
+
+	if ((uintptr_t)dst % sizeof(long) == 0 &&
+	    (uintptr_t)src % sizeof(long) == 0 &&
+	    len % sizeof(long) == 0) {
+
+		long *d = dst;
+		const long *s = src;
+
+		/*
+		 * The reason we copy index i-1 and test i>0 is that
+		 * i is unsigned -- so testing i>=0 doesn't work.
+		 */
+
+		for (i=len/sizeof(long); i>0; i--) {
+			d[i-1] = s[i-1];
+		}
+	}
+	else {
+		char *d = dst;
+		const char *s = src;
+
+		for (i=len; i>0; i--) {
+			d[i-1] = s[i-1];
+		}
+	}
+
+	return dst;
+}