Chris Zankel writes:

The following patches add support for the Xtensa processor architecture
to uClibc. They are based on a recent SVN checkout (12/05/2007).

The first patch (attached to this post) adds Xtensa support to various
shared configuration and make files. The following patches then include
the Xtensa specific files and directories.

I welcome any feedback and would appreciate it if you could include the
patches into the mainline tree. I am certainly committed to maintain the port. 

Bob Wilson was kind enough to review the patches.

Some notes about the architecture: Xtensa is a configurable and
extensible processor architecture developed by Tensilica. For more
information, please visit: www.linux-xtensa.org.

1 files changed, 104 insertions, 0 deletions

diff --git a/libc/string/xtensa/strlen.S b/libc/string/xtensa/strlen.S
new file mode 100644
index 000000000..dd72c16fa
--- /dev/null
+++ b/libc/string/xtensa/strlen.S
@@ -0,0 +1,104 @@
+/* Optimized strlen for Xtensa.
+   Copyright (C) 2001, 2007 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
+   Boston, MA 02110-1301, USA.  */
+
+#include "../../sysdeps/linux/xtensa/sysdep.h"
+#include <bits/xtensa-config.h>
+
+#ifdef __XTENSA_EB__
+#define	MASK0 0xff000000
+#define	MASK1 0x00ff0000
+#define	MASK2 0x0000ff00
+#define	MASK3 0x000000ff
+#else
+#define	MASK0 0x000000ff
+#define	MASK1 0x0000ff00
+#define	MASK2 0x00ff0000
+#define	MASK3 0xff000000
+#endif
+
+	.text
+ENTRY (strlen)
+	/* a2 = s */
+
+	addi	a3, a2, -4	// because we overincrement at the end
+	movi	a4, MASK0
+	movi	a5, MASK1
+	movi	a6, MASK2
+	movi	a7, MASK3
+	bbsi.l	a2, 0, .L1mod2
+	bbsi.l	a2, 1, .L2mod4
+	j	.Laligned
+
+.L1mod2: // address is odd
+	l8ui	a8, a3, 4	// get byte 0
+	addi	a3, a3, 1	// advance string pointer
+	beqz	a8, .Lz3	// if byte 0 is zero
+	bbci.l	a3, 1, .Laligned // if string pointer is now word-aligned
+
+.L2mod4: // address is 2 mod 4
+	addi	a3, a3, 2	// advance ptr for aligned access
+	l32i	a8, a3, 0	// get word with first two bytes of string
+	bnone	a8, a6, .Lz2	// if byte 2 (of word, not string) is zero
+	bany	a8, a7, .Laligned // if byte 3 (of word, not string) is nonzero
+
+	/* Byte 3 is zero.  */
+	addi	a3, a3, 3	// point to zero byte
+	sub	a2, a3, a2	// subtract to get length
+	retw
+
+
+/* String is word-aligned.  */
+
+	.align	4
+	/* (2 mod 4) alignment for loop instruction */
+.Laligned:
+#if XCHAL_HAVE_LOOPS
+	_movi.n	a8, 0		// set up for the maximum loop count
+	loop	a8, .Lz3	// loop forever (almost anyway)
+#endif
+1:	l32i	a8, a3, 4	// get next word of string
+	addi	a3, a3, 4	// advance string pointer
+	bnone	a8, a4, .Lz0	// if byte 0 is zero
+	bnone	a8, a5, .Lz1	// if byte 1 is zero
+	bnone	a8, a6, .Lz2	// if byte 2 is zero
+#if XCHAL_HAVE_LOOPS
+	bnone	a8, a7, .Lz3	// if byte 3 is zero
+#else
+	bany	a8, a7, 1b	// repeat if byte 3 is non-zero
+#endif
+
+.Lz3:	/* Byte 3 is zero.  */
+	addi	a3, a3, 3	// point to zero byte
+	/* Fall through....  */
+
+.Lz0:	/* Byte 0 is zero.  */
+	sub	a2, a3, a2	// subtract to get length
+	retw
+
+.Lz1:	/* Byte 1 is zero.  */
+	addi	a3, a3, 1	// point to zero byte
+	sub	a2, a3, a2	// subtract to get length
+	retw
+
+.Lz2:	/* Byte 2 is zero.  */
+	addi	a3, a3, 2	// point to zero byte
+	sub	a2, a3, a2	// subtract to get length
+	retw
+
+libc_hidden_def (strlen)