Merge "libc: memset: improve performance by avoiding single byte writes" into integration

lib/libc/memset.c

@@ -1,18 +1,48 @@
 /*
- * Copyright (c) 2013-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2020, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
 #include <stddef.h>
 #include <string.h>
+#include <stdint.h>
 
 void *memset(void *dst, int val, size_t count)
 {
 	char *ptr = dst;
+	uint64_t *ptr64;
+	uint64_t fill = (unsigned char)val;
 
-	while (count--)
+	/* Simplify code below by making sure we write at least one byte. */
+	if (count == 0) {
+		return dst;
+	}
+
+	/* Handle the first part, until the pointer becomes 64-bit aligned. */
+	while (((uintptr_t)ptr & 7)) {
+		*ptr++ = val;
+		if (--count == 0) {
+			return dst;
+		}
+	}
+
+	/* Duplicate the fill byte to the rest of the 64-bit word. */
+	fill |= fill << 8;
+	fill |= fill << 16;
+	fill |= fill << 32;
+
+	/* Use 64-bit writes for as long as possible. */
+	ptr64 = (void *)ptr;
+	for (; count >= 8; count -= 8) {
+		*ptr64++ = fill;
+	}
+
+	/* Handle the remaining part byte-per-byte. */
+	ptr = (void *)ptr64;
+	while (count--) {
 		*ptr++ = val;
+	}
 
 	return dst;
 }