x86: Import the glibc memset implementation

The new implementation is about twice as fast as the old. This is from
glibc-2.14, sysdeps/i386/memset.c.

Signed-off-by: Gabe Black <gabeblack@chromium.org>

1 files changed, 87 insertions, 0 deletions

diff --git a/arch/x86/lib/string.c b/arch/x86/lib/string.c
new file mode 100644
index 0000000..f2ea7e4
--- /dev/null
+++ b/arch/x86/lib/string.c
@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 1991,1992,1993,1997,1998,2003, 2005 Free Software Foundation, Inc.
+ * This file is part of the GNU C Library.
+ * Copyright (c) 2011 The Chromium OS Authors.
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+/* From glibc-2.14, sysdeps/i386/memset.c */
+
+#include <compiler.h>
+#include <asm/string.h>
+#include <linux/types.h>
+
+typedef uint32_t op_t;
+
+void *memset(void *dstpp, int c, size_t len)
+{
+	int d0;
+	unsigned long int dstp = (unsigned long int) dstpp;
+
+	/* This explicit register allocation improves code very much indeed. */
+	register op_t x asm("ax");
+
+	x = (unsigned char) c;
+
+	/* Clear the direction flag, so filling will move forward.  */
+	asm volatile("cld");
+
+	/* This threshold value is optimal.  */
+	if (len >= 12) {
+		/* Fill X with four copies of the char we want to fill with. */
+		x |= (x << 8);
+		x |= (x << 16);
+
+		/* Adjust LEN for the bytes handled in the first loop.  */
+		len -= (-dstp) % sizeof(op_t);
+
+		/*
+		 * There are at least some bytes to set. No need to test for
+		 * LEN == 0 in this alignment loop.
+		 */
+
+		/* Fill bytes until DSTP is aligned on a longword boundary. */
+		asm volatile(
+			"rep\n"
+			"stosb" /* %0, %2, %3 */ :
+			"=D" (dstp), "=c" (d0) :
+			"0" (dstp), "1" ((-dstp) % sizeof(op_t)), "a" (x) :
+			"memory");
+
+		/* Fill longwords.  */
+		asm volatile(
+			"rep\n"
+			"stosl" /* %0, %2, %3 */ :
+			"=D" (dstp), "=c" (d0) :
+			"0" (dstp), "1" (len / sizeof(op_t)), "a" (x) :
+			"memory");
+		len %= sizeof(op_t);
+	}
+
+	/* Write the last few bytes. */
+	asm volatile(
+		"rep\n"
+		"stosb" /* %0, %2, %3 */ :
+		"=D" (dstp), "=c" (d0) :
+		"0" (dstp), "1" (len), "a" (x) :
+		"memory");
+
+	return dstpp;
+}