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, 165 insertions, 0 deletions

diff --git a/libc/string/xtensa/memset.S b/libc/string/xtensa/memset.S
new file mode 100644
index 000000000..c0928825d
--- /dev/null
+++ b/libc/string/xtensa/memset.S
@@ -0,0 +1,165 @@
+/* Optimized memset 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>
+
+/* Do not use .literal_position in the ENTRY macro.  */
+#undef LITERAL_POSITION
+#define LITERAL_POSITION
+
+/* void *memset (void *dst, int c, size_t length)
+
+   The algorithm is as follows:
+
+   Create a word with c in all byte positions.
+	
+   If the destination is aligned, set 16B chunks with a loop, and then
+   finish up with 8B, 4B, 2B, and 1B stores conditional on the length.
+
+   If the destination is unaligned, align it by conditionally
+   setting 1B and/or 2B and then go to aligned case.
+
+   This code tries to use fall-through branches for the common
+   case of an aligned destination (except for the branches to
+   the alignment labels).  */
+
+
+/* Byte-by-byte set.  */
+
+	.text
+	.align	4
+	.literal_position
+__memset_aux:
+
+	/* Skip a byte to get 1 mod 4 alignment for LOOPNEZ
+	   (0 mod 4 alignment for LBEG).  */
+	.byte	0
+
+.Lbyteset:
+#if XCHAL_HAVE_LOOPS
+	loopnez	a4, 2f
+#else
+	beqz	a4, 2f
+	add	a6, a5, a4	// a6 = ending address
+#endif
+1:	s8i	a3, a5, 0
+	addi	a5, a5, 1
+#if !XCHAL_HAVE_LOOPS
+	blt	a5, a6, 1b
+#endif
+2:	retw
+
+
+/* Destination is unaligned.  */
+
+	.align	4
+
+.Ldst1mod2: // dst is only byte aligned
+
+	/* Do short sizes byte-by-byte.  */
+	bltui	a4, 8, .Lbyteset
+
+	/* Set 1 byte.  */
+	s8i	a3, a5, 0
+	addi	a5, a5, 1
+	addi	a4, a4, -1
+
+	/* Now retest if dst is aligned.  */
+	_bbci.l	a5, 1, .Ldstaligned
+
+.Ldst2mod4: // dst has 16-bit alignment
+
+	/* Do short sizes byte-by-byte.  */
+	bltui	a4, 8, .Lbyteset
+
+	/* Set 2 bytes.  */
+	s16i	a3, a5, 0
+	addi	a5, a5, 2
+	addi	a4, a4, -2
+
+	/* dst is now aligned; return to main algorithm */
+	j	.Ldstaligned
+
+
+ENTRY (memset)
+	/* a2 = dst, a3 = c, a4 = length */
+
+	/* Duplicate character into all bytes of word.  */
+	extui	a3, a3, 0, 8
+	slli	a7, a3, 8
+	or	a3, a3, a7
+	slli	a7, a3, 16
+	or	a3, a3, a7
+
+	mov	a5, a2		// copy dst so that a2 is return value
+
+	/* Check if dst is unaligned.  */
+	_bbsi.l	a2, 0, .Ldst1mod2
+	_bbsi.l	a2, 1, .Ldst2mod4
+.Ldstaligned:
+
+	/* Get number of loop iterations with 16B per iteration.  */
+	srli	a7, a4, 4
+
+	/* Destination is word-aligned.  */
+#if XCHAL_HAVE_LOOPS
+	loopnez	a7, 2f
+#else
+	beqz	a7, 2f
+	slli	a6, a7, 4
+	add	a6, a6, a5	// a6 = end of last 16B chunk
+#endif
+	/* Set 16 bytes per iteration.  */
+1:	s32i	a3, a5, 0
+	s32i	a3, a5, 4
+	s32i	a3, a5, 8
+	s32i	a3, a5, 12
+	addi	a5, a5, 16
+#if !XCHAL_HAVE_LOOPS
+	blt	a5, a6, 1b
+#endif
+
+	/* Set any leftover pieces smaller than 16B.  */
+2:	bbci.l	a4, 3, 3f
+
+	/* Set 8 bytes.  */
+	s32i	a3, a5, 0
+	s32i	a3, a5, 4
+	addi	a5, a5, 8
+
+3:	bbci.l	a4, 2, 4f
+
+	/* Set 4 bytes.  */
+	s32i	a3, a5, 0
+	addi	a5, a5, 4
+
+4:	bbci.l	a4, 1, 5f
+
+	/* Set 2 bytes.  */
+	s16i	a3, a5, 0
+	addi	a5, a5, 2
+
+5:	bbci.l	a4, 0, 6f
+
+	/* Set 1 byte.  */
+	s8i	a3, a5, 0
+6:	retw
+
+libc_hidden_def (memset)