Message-ID: <4C7E2CA9.9060702@cn.fujitsu.com>
Date:	Wed, 01 Sep 2010 18:36:25 +0800
From:	Miao Xie <miaox@...fujitsu.com>
To:	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Mason <chris.mason@...cle.com>,
	"Theodore Ts'o" <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Btrfs <linux-btrfs@...r.kernel.org>,
	Linux Ext4 <linux-ext4@...r.kernel.org>
Subject: [PATCH 1/3] lib: introduce some memory copy macros and functions

the kernel's memcpy and memmove is very inefficient. But the glibc version is
quite fast, in some cases it is 10 times faster than the kernel version. So I
introduce some memory copy macros and functions of the glibc to improve the
kernel version's performance.

The strategy of the memory functions is:
1. Copy bytes until the destination pointer is aligned.
2. Copy words in unrolled loops.  If the source and destination are not aligned
   in the same way, use word memory operations, but shift and merge two read
   words before writing.
3. Copy the few remaining bytes.

Signed-off-by: Miao Xie <miaox@...fujitsu.com>
---
 include/linux/memcopy.h |  226 ++++++++++++++++++++++++++
 lib/Makefile            |    3 +-
 lib/memcopy.c           |  403 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 631 insertions(+), 1 deletions(-)
 create mode 100644 include/linux/memcopy.h
 create mode 100644 lib/memcopy.c

diff --git a/include/linux/memcopy.h b/include/linux/memcopy.h
new file mode 100644
index 0000000..9c65ac8
--- /dev/null
+++ b/include/linux/memcopy.h
@@ -0,0 +1,226 @@
+/*
+ * memcopy.h -- definitions for memory copy functions.  Generic C version.
+ *
+ * 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 2.1 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.
+ *
+ * The code is derived from the GNU C Library.
+ * Copyright (C) 1991, 1992, 1993, 1997, 2004 Free Software Foundation, Inc.
+ */
+#ifndef _LINUX_MEMCOPY_H_
+#define _LINUX_MEMCOPY_H_
+
+/*
+ * The strategy of the memory functions is:
+ *
+ *   1. Copy bytes until the destination pointer is aligned.
+ *
+ *   2. Copy words in unrolled loops.  If the source and destination
+ *      are not aligned in the same way, use word memory operations,
+ *      but shift and merge two read words before writing.
+ *
+ *   3. Copy the few remaining bytes.
+ *
+ * This is fast on processors that have at least 10 registers for
+ * allocation by GCC, and that can access memory at reg+const in one
+ * instruction.
+ */
+
+#include <linux/types.h>
+#include <linux/compiler.h>
+#include <asm/byteorder.h>
+
+/*
+ * The macros defined in this file are:
+ *
+ * BYTE_COPY_FWD(dst_beg_ptr, src_beg_ptr, nbytes_to_copy)
+ * 
+ * BYTE_COPY_BWD(dst_end_ptr, src_end_ptr, nbytes_to_copy)
+ * 
+ * WORD_COPY_FWD(dst_beg_ptr, src_beg_ptr, nbytes_remaining, nbytes_to_copy)
+ * 
+ * WORD_COPY_BWD(dst_end_ptr, src_end_ptr, nbytes_remaining, nbytes_to_copy)
+ * 
+ * MERGE(old_word, sh_1, new_word, sh_2)
+ * 
+ * MEM_COPY_FWD(dst_beg_ptr, src_beg_ptr, nbytes_to_copy)
+ * 
+ * MEM_COPY_BWD(dst_end_ptr, src_end_ptr, nbytes_to_copy)
+ */
+
+#define OP_T_THRESHOLD	16
+
+/*
+ * Type to use for aligned memory operations.
+ * This should normally be the biggest type supported by a single load
+ * and store.
+ */
+#define	op_t	unsigned long int
+#define OPSIZ	(sizeof(op_t))
+
+/* Type to use for unaligned operations.  */
+typedef unsigned char byte;
+
+#ifndef MERGE
+# ifdef __LITTLE_ENDIAN
+#  define MERGE(w0, sh_1, w1, sh_2) (((w0) >> (sh_1)) | ((w1) << (sh_2)))
+# elif defined(__BIG_ENDIAN)
+#  define MERGE(w0, sh_1, w1, sh_2) (((w0) << (sh_1)) | ((w1) >> (sh_2)))
+# else
+#  error "Macro MERGE() hasn't defined!"
+# endif
+#endif
+
+/*
+ * Copy exactly NBYTES bytes from SRC_BP to DST_BP,
+ * without any assumptions about alignment of the pointers.
+ */
+#ifndef BYTE_COPY_FWD
+#define BYTE_COPY_FWD(dst_bp, src_bp, nbytes)				      \
+do {									      \
+	size_t __nbytes = (nbytes);					      \
+	while (__nbytes > 0) {						      \
+		byte __x = ((byte *) src_bp)[0];			      \
+		src_bp += 1;						      \
+		__nbytes -= 1;						      \
+		((byte *) dst_bp)[0] = __x;				      \
+		dst_bp += 1;						      \
+	}								      \
+} while (0)
+#endif
+
+/*
+ * Copy exactly NBYTES_TO_COPY bytes from SRC_END_PTR to DST_END_PTR,
+ * beginning at the bytes right before the pointers and continuing towards
+ * smaller addresses.  Don't assume anything about alignment of the
+ * pointers.
+ */
+#ifndef BYTE_COPY_BWD
+#define BYTE_COPY_BWD(dst_ep, src_ep, nbytes)				      \
+do {									      \
+	size_t __nbytes = (nbytes);					      \
+	while (__nbytes > 0) {						      \
+		byte __x;						      \
+		src_ep -= 1;						      \
+		__x = ((byte *) src_ep)[0];				      \
+		dst_ep -= 1;						      \
+		__nbytes -= 1;						      \
+		((byte *) dst_ep)[0] = __x;				      \
+	}								      \
+} while (0)
+#endif
+/*
+ * Copy *up to* NBYTES bytes from SRC_BP to DST_BP, with
+ * the assumption that DST_BP is aligned on an OPSIZ multiple.  If
+ * not all bytes could be easily copied, store remaining number of bytes
+ * in NBYTES_LEFT, otherwise store 0.
+ */
+extern void _wordcopy_fwd_aligned(long int, long int, size_t);
+extern void _wordcopy_fwd_dest_aligned(long int, long int, size_t);
+#ifndef WORD_COPY_FWD
+#define WORD_COPY_FWD(dst_bp, src_bp, nbytes_left, nbytes)		      \
+do {									      \
+	if (src_bp % OPSIZ == 0)					      \
+		_wordcopy_fwd_aligned (dst_bp, src_bp, (nbytes) / OPSIZ);     \
+	else								      \
+		_wordcopy_fwd_dest_aligned (dst_bp, src_bp, (nbytes) / OPSIZ);\
+									      \
+	src_bp += (nbytes) & -OPSIZ;					      \
+	dst_bp += (nbytes) & -OPSIZ;					      \
+	(nbytes_left) = (nbytes) % OPSIZ;				      \
+} while (0)
+#endif
+
+/*
+ * Copy *up to* NBYTES_TO_COPY bytes from SRC_END_PTR to DST_END_PTR,
+ * beginning at the words (of type op_t) right before the pointers and
+ * continuing towards smaller addresses.  May take advantage of that
+ * DST_END_PTR is aligned on an OPSIZ multiple.  If not all bytes could be
+ * easily copied, store remaining number of bytes in NBYTES_REMAINING,
+ * otherwise store 0.
+ */
+extern void _wordcopy_bwd_aligned(long int, long int, size_t);
+extern void _wordcopy_bwd_dest_aligned(long int, long int, size_t);
+#ifndef WORD_COPY_BWD
+#define WORD_COPY_BWD(dst_ep, src_ep, nbytes_left, nbytes)		      \
+do {									      \
+	if (src_ep % OPSIZ == 0)					      \
+		_wordcopy_bwd_aligned (dst_ep, src_ep, (nbytes) / OPSIZ);     \
+	else								      \
+		_wordcopy_bwd_dest_aligned (dst_ep, src_ep, (nbytes) / OPSIZ);\
+									      \
+	src_ep -= (nbytes) & -OPSIZ;					      \
+	dst_ep -= (nbytes) & -OPSIZ;					      \
+	(nbytes_left) = (nbytes) % OPSIZ;				      \
+} while (0)
+#endif
+
+/* Copy memory from the beginning to the end */
+#ifndef MEM_COPY_FWD
+static __always_inline void mem_copy_fwd(unsigned long dstp,
+					unsigned long srcp,
+					size_t count)
+{
+	/* If there not too few bytes to copy, use word copy. */
+	if (count >= OP_T_THRESHOLD) {
+		/* Copy just a few bytes to make dstp aligned. */
+		count -= (-dstp) % OPSIZ;
+		BYTE_COPY_FWD(dstp, srcp, (-dstp) % OPSIZ);
+
+		/*
+		 * Copy from srcp to dstp taking advantage of the known
+		 * alignment of dstp. Number if bytes remaining is put in
+		 * the third argument.
+		 */
+		WORD_COPY_FWD(dstp, srcp, count, count);
+
+		/* Fall out and copy the tail. */
+	}
+
+	/* There are just a few bytes to copy. Use byte memory operations. */
+	BYTE_COPY_FWD(dstp, srcp, count);
+}
+#endif
+
+/* Copy memory from the end to the beginning.  */
+#ifndef MEM_COPY_BWD
+static __always_inline void mem_copy_bwd(unsigned long dstp,
+					unsigned long srcp,
+					size_t count)
+{
+	srcp += count;
+	dstp += count;
+
+	/* If there not too few bytes to copy, use word copy. */
+	if (count >= OP_T_THRESHOLD) {
+		/* Copy just a few bytes to make dstp aligned. */
+		count -= dstp % OPSIZ;
+		BYTE_COPY_BWD(dstp, srcp, dstp % OPSIZ);
+
+		/*
+		 * Copy from srcp to dstp taking advantage of the known
+		 * alignment of dstp. Number if bytes remaining is put in
+		 * the third argument.
+		 */
+		WORD_COPY_BWD(dstp, srcp, count, count);
+
+		/* Fall out and copy the tail. */
+	}
+
+	/* There are just a few bytes to copy. Use byte memory operations. */
+	BYTE_COPY_BWD (dstp, srcp, count);
+}
+#endif
+
+#endif
diff --git a/lib/Makefile b/lib/Makefile
index e6a3763..10a319e 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -12,7 +12,8 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
 	 idr.o int_sqrt.o extable.o prio_tree.o \
 	 sha1.o irq_regs.o reciprocal_div.o argv_split.o \
 	 proportions.o prio_heap.o ratelimit.o show_mem.o \
-	 is_single_threaded.o plist.o decompress.o flex_array.o
+	 is_single_threaded.o plist.o decompress.o flex_array.o \
+	 memcopy.o
 
 lib-$(CONFIG_MMU) += ioremap.o
 lib-$(CONFIG_SMP) += cpumask.o
diff --git a/lib/memcopy.c b/lib/memcopy.c
new file mode 100644
index 0000000..70fb6b2
--- /dev/null
+++ b/lib/memcopy.c
@@ -0,0 +1,403 @@
+/*
+ * memcopy.c -- subroutines for memory copy functions.
+ *
+ * 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 2.1 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.
+ *
+ * The code is derived from the GNU C Library.
+ * Copyright (C) 1991, 1992, 1993, 1997, 2004 Free Software Foundation, Inc.
+ */
+
+/* BE VERY CAREFUL IF YOU CHANGE THIS CODE...!  */
+
+#include <linux/memcopy.h>
+
+/*
+ * _wordcopy_fwd_aligned -- Copy block beginning at SRCP to block beginning
+ * at DSTP with LEN `op_t' words (not LEN bytes!).
+ * Both SRCP and DSTP should be aligned for memory operations on `op_t's.
+ */
+void _wordcopy_fwd_aligned (long int dstp, long int srcp, size_t len)
+{
+	op_t a0, a1;
+
+	switch (len % 8) {
+	case 2:
+		a0 = ((op_t *) srcp)[0];
+		srcp -= 6 * OPSIZ;
+		dstp -= 7 * OPSIZ;
+		len += 6;
+		goto do1;
+	case 3:
+		a1 = ((op_t *) srcp)[0];
+		srcp -= 5 * OPSIZ;
+		dstp -= 6 * OPSIZ;
+		len += 5;
+		goto do2;
+	case 4:
+		a0 = ((op_t *) srcp)[0];
+		srcp -= 4 * OPSIZ;
+		dstp -= 5 * OPSIZ;
+		len += 4;
+		goto do3;
+	case 5:
+		a1 = ((op_t *) srcp)[0];
+		srcp -= 3 * OPSIZ;
+		dstp -= 4 * OPSIZ;
+		len += 3;
+		goto do4;
+	case 6:
+		a0 = ((op_t *) srcp)[0];
+		srcp -= 2 * OPSIZ;
+		dstp -= 3 * OPSIZ;
+		len += 2;
+		goto do5;
+	case 7:
+		a1 = ((op_t *) srcp)[0];
+		srcp -= 1 * OPSIZ;
+		dstp -= 2 * OPSIZ;
+		len += 1;
+		goto do6;
+	case 0:
+		if (OP_T_THRESHOLD <= 3 * OPSIZ && len == 0)
+			return;
+		a0 = ((op_t *) srcp)[0];
+		srcp -= 0 * OPSIZ;
+		dstp -= 1 * OPSIZ;
+		goto do7;
+	case 1:
+		a1 = ((op_t *) srcp)[0];
+		srcp -=-1 * OPSIZ;
+		dstp -= 0 * OPSIZ;
+		len -= 1;
+		if (OP_T_THRESHOLD <= 3 * OPSIZ && len == 0)
+			goto do0;
+		goto do8;			/* No-op.  */
+	}
+
+	do {
+do8:
+		a0 = ((op_t *) srcp)[0];
+		((op_t *) dstp)[0] = a1;
+do7:
+		a1 = ((op_t *) srcp)[1];
+		((op_t *) dstp)[1] = a0;
+do6:
+		a0 = ((op_t *) srcp)[2];
+		((op_t *) dstp)[2] = a1;
+do5:
+		a1 = ((op_t *) srcp)[3];
+		((op_t *) dstp)[3] = a0;
+do4:
+		a0 = ((op_t *) srcp)[4];
+		((op_t *) dstp)[4] = a1;
+do3:
+		a1 = ((op_t *) srcp)[5];
+		((op_t *) dstp)[5] = a0;
+do2:
+		a0 = ((op_t *) srcp)[6];
+		((op_t *) dstp)[6] = a1;
+do1:
+		a1 = ((op_t *) srcp)[7];
+		((op_t *) dstp)[7] = a0;
+
+		srcp += 8 * OPSIZ;
+		dstp += 8 * OPSIZ;
+		len -= 8;
+	} while (len != 0);
+
+	/*
+	 * This is the right position for do0.  Please don't move it into
+	 * the loop.
+	 */
+do0:
+	((op_t *) dstp)[0] = a1;
+}
+
+/*
+ * _wordcopy_fwd_dest_aligned -- Copy block beginning at SRCP to block
+ * beginning at DSTP with LEN `op_t' words (not LEN bytes!). DSTP should
+ * be aligned for memory operations on `op_t's, but SRCP must *not* be aligned.
+ */
+
+void _wordcopy_fwd_dest_aligned (long int dstp, long int srcp, size_t len)
+{
+	op_t a0, a1, a2, a3;
+	int sh_1, sh_2;
+
+	/*
+	 * Calculate how to shift a word read at the memory operation aligned
+	 * srcp to make it aligned for copy.
+	 */
+	sh_1 = 8 * (srcp % OPSIZ);
+	sh_2 = 8 * OPSIZ - sh_1;
+
+	/*
+	 * Make SRCP aligned by rounding it down to the beginning of the `op_t'
+	 * it points in the middle of.
+	 */
+	srcp &= -OPSIZ;
+
+	switch (len % 4) {
+	case 2:
+		a1 = ((op_t *) srcp)[0];
+		a2 = ((op_t *) srcp)[1];
+		srcp -= 1 * OPSIZ;
+		dstp -= 3 * OPSIZ;
+		len += 2;
+		goto do1;
+	case 3:
+		a0 = ((op_t *) srcp)[0];
+		a1 = ((op_t *) srcp)[1];
+		srcp -= 0 * OPSIZ;
+		dstp -= 2 * OPSIZ;
+		len += 1;
+		goto do2;
+	case 0:
+		if (OP_T_THRESHOLD <= 3 * OPSIZ && len == 0)
+			return;
+		a3 = ((op_t *) srcp)[0];
+		a0 = ((op_t *) srcp)[1];
+		srcp -=-1 * OPSIZ;
+		dstp -= 1 * OPSIZ;
+		len += 0;
+		goto do3;
+	case 1:
+		a2 = ((op_t *) srcp)[0];
+		a3 = ((op_t *) srcp)[1];
+		srcp -=-2 * OPSIZ;
+		dstp -= 0 * OPSIZ;
+		len -= 1;
+		if (OP_T_THRESHOLD <= 3 * OPSIZ && len == 0)
+			goto do0;
+		goto do4;			/* No-op. */
+	}
+
+	do {
+do4:
+		a0 = ((op_t *) srcp)[0];
+		((op_t *) dstp)[0] = MERGE (a2, sh_1, a3, sh_2);
+do3:
+		a1 = ((op_t *) srcp)[1];
+		((op_t *) dstp)[1] = MERGE (a3, sh_1, a0, sh_2);
+do2:
+		a2 = ((op_t *) srcp)[2];
+		((op_t *) dstp)[2] = MERGE (a0, sh_1, a1, sh_2);
+do1:
+		a3 = ((op_t *) srcp)[3];
+		((op_t *) dstp)[3] = MERGE (a1, sh_1, a2, sh_2);
+
+		srcp += 4 * OPSIZ;
+		dstp += 4 * OPSIZ;
+		len -= 4;
+	} while (len != 0);
+
+	/*
+	 * This is the right position for do0.  Please don't move it into
+	 * the loop.
+	 */
+do0:
+	((op_t *) dstp)[0] = MERGE (a2, sh_1, a3, sh_2);
+}
+
+/*
+ * _wordcopy_bwd_aligned -- Copy block finishing right before
+ * SRCP to block finishing right before DSTP with LEN `op_t' words (not LEN
+ * bytes!).  Both SRCP and DSTP should be aligned for memory operations
+ * on `op_t's.
+ */
+void _wordcopy_bwd_aligned (long int dstp, long int srcp, size_t len)
+{
+	op_t a0, a1;
+
+	switch (len % 8) {
+	case 2:
+		srcp -= 2 * OPSIZ;
+		dstp -= 1 * OPSIZ;
+		a0 = ((op_t *) srcp)[1];
+		len += 6;
+		goto do1;
+	case 3:
+		srcp -= 3 * OPSIZ;
+		dstp -= 2 * OPSIZ;
+		a1 = ((op_t *) srcp)[2];
+		len += 5;
+		goto do2;
+	case 4:
+		srcp -= 4 * OPSIZ;
+		dstp -= 3 * OPSIZ;
+		a0 = ((op_t *) srcp)[3];
+		len += 4;
+		goto do3;
+	case 5:
+		srcp -= 5 * OPSIZ;
+		dstp -= 4 * OPSIZ;
+		a1 = ((op_t *) srcp)[4];
+		len += 3;
+		goto do4;
+	case 6:
+		srcp -= 6 * OPSIZ;
+		dstp -= 5 * OPSIZ;
+		a0 = ((op_t *) srcp)[5];
+		len += 2;
+		goto do5;
+	case 7:
+		srcp -= 7 * OPSIZ;
+		dstp -= 6 * OPSIZ;
+		a1 = ((op_t *) srcp)[6];
+		len += 1;
+		goto do6;
+	case 0:
+		if (OP_T_THRESHOLD <= 3 * OPSIZ && len == 0)
+			return;
+		srcp -= 8 * OPSIZ;
+		dstp -= 7 * OPSIZ;
+		a0 = ((op_t *) srcp)[7];
+		goto do7;
+	case 1:
+		srcp -= 9 * OPSIZ;
+		dstp -= 8 * OPSIZ;
+		a1 = ((op_t *) srcp)[8];
+		len -= 1;
+		if (OP_T_THRESHOLD <= 3 * OPSIZ && len == 0)
+			goto do0;
+		goto do8;			/* No-op.  */
+	}
+
+	do {
+do8:
+		a0 = ((op_t *) srcp)[7];
+		((op_t *) dstp)[7] = a1;
+do7:
+		a1 = ((op_t *) srcp)[6];
+		((op_t *) dstp)[6] = a0;
+do6:
+		a0 = ((op_t *) srcp)[5];
+		((op_t *) dstp)[5] = a1;
+do5:
+		a1 = ((op_t *) srcp)[4];
+		((op_t *) dstp)[4] = a0;
+do4:
+		a0 = ((op_t *) srcp)[3];
+		((op_t *) dstp)[3] = a1;
+do3:
+		a1 = ((op_t *) srcp)[2];
+		((op_t *) dstp)[2] = a0;
+do2:
+		a0 = ((op_t *) srcp)[1];
+		((op_t *) dstp)[1] = a1;
+do1:
+		a1 = ((op_t *) srcp)[0];
+		((op_t *) dstp)[0] = a0;
+
+		srcp -= 8 * OPSIZ;
+		dstp -= 8 * OPSIZ;
+		len -= 8;
+	} while (len != 0);
+
+	/*
+	 * This is the right position for do0.  Please don't move it into
+	 * the loop.
+	 */
+do0:
+	((op_t *) dstp)[7] = a1;
+}
+
+/*
+ * _wordcopy_bwd_dest_aligned -- Copy block finishing right before SRCP to
+ * block finishing right before DSTP with LEN `op_t' words (not LEN bytes!).
+ * DSTP should be aligned for memory operations on `op_t', but SRCP must *not*
+ * be aligned.
+ */
+void _wordcopy_bwd_dest_aligned (long int dstp, long int srcp, size_t len)
+{
+	op_t a0, a1, a2, a3;
+	int sh_1, sh_2;
+
+	/*
+	 * Calculate how to shift a word read at the memory operation aligned
+	 * srcp to make it aligned for copy.
+	 */
+
+	sh_1 = 8 * (srcp % OPSIZ);
+	sh_2 = 8 * OPSIZ - sh_1;
+
+	/*
+	 * Make srcp aligned by rounding it down to the beginning of the op_t
+	 * it points in the middle of.
+	 */
+	srcp &= -OPSIZ;
+	srcp += OPSIZ;
+
+	switch (len % 4) {
+	case 2:
+		srcp -= 3 * OPSIZ;
+		dstp -= 1 * OPSIZ;
+		a2 = ((op_t *) srcp)[2];
+		a1 = ((op_t *) srcp)[1];
+		len += 2;
+		goto do1;
+	case 3:
+		srcp -= 4 * OPSIZ;
+		dstp -= 2 * OPSIZ;
+		a3 = ((op_t *) srcp)[3];
+		a2 = ((op_t *) srcp)[2];
+		len += 1;
+		goto do2;
+	case 0:
+		if (OP_T_THRESHOLD <= 3 * OPSIZ && len == 0)
+			return;
+		srcp -= 5 * OPSIZ;
+		dstp -= 3 * OPSIZ;
+		a0 = ((op_t *) srcp)[4];
+		a3 = ((op_t *) srcp)[3];
+		goto do3;
+	case 1:
+		srcp -= 6 * OPSIZ;
+		dstp -= 4 * OPSIZ;
+		a1 = ((op_t *) srcp)[5];
+		a0 = ((op_t *) srcp)[4];
+		len -= 1;
+		if (OP_T_THRESHOLD <= 3 * OPSIZ && len == 0)
+			goto do0;
+		goto do4;			/* No-op.  */
+	}
+
+	do {
+do4:
+		a3 = ((op_t *) srcp)[3];
+		((op_t *) dstp)[3] = MERGE (a0, sh_1, a1, sh_2);
+do3:
+		a2 = ((op_t *) srcp)[2];
+		((op_t *) dstp)[2] = MERGE (a3, sh_1, a0, sh_2);
+do2:
+		a1 = ((op_t *) srcp)[1];
+		((op_t *) dstp)[1] = MERGE (a2, sh_1, a3, sh_2);
+do1:
+		a0 = ((op_t *) srcp)[0];
+		((op_t *) dstp)[0] = MERGE (a1, sh_1, a2, sh_2);
+
+		srcp -= 4 * OPSIZ;
+		dstp -= 4 * OPSIZ;
+		len -= 4;
+	} while (len != 0);
+
+	/*
+	 * This is the right position for do0.  Please don't move it into
+	 * the loop.
+	 */
+do0:
+	((op_t *) dstp)[3] = MERGE (a0, sh_1, a1, sh_2);
+}
+
-- 
1.7.0.1
--
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