Optimization for strncpy and stpncpy on Power7
diff mbox

Message ID 1399057865-9822-1-git-send-email-vidya@linux.vnet.ibm.com
State New
Headers show

Commit Message

vidya@linux.vnet.ibm.com May 2, 2014, 7:11 p.m. UTC
From: Vidya Ranganathan <vidya@linux.vnet.ibm.com>

The optimization is achieved by following techniques:
   > data alignment [gain from aligned memory access on read/write]
   > prefetch data [gain from cache misses by anticipating load]
   > POWER7 gains performance with loop unrolling/unwinding
      [gain by reduction of branch penalty].

ChangeLog:
2014-04-27  Vidya Ranganathan  <vidya@linux.vnet.ibm.com>

	* sysdeps/powerpc/powerpc64/power7/strncpy.S: New file: Optimization.
	* sysdeps/powerpc/powerpc64/multiarch/strncpy.c: New file:
	multiarch strncpy for PPC64.
	* sysdeps/powerpc/powerpc64/multiarch/strncpy-ppc64.c: New file
	* sysdeps/powerpc/powerpc64/multiarch/strncpy-power7.S: New file
	* sysdeps/powerpc/powerpc64/multiarch/Makefile: Add strpcpy, stpncpy
	multiarch optimizations.
	* sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c:
	(__libc_ifunc_impl_list): Likewise.
	* sysdeps/powerpc/powerpc64/power7/stpncpy.S: New file: Optimization.
	* sysdeps/powerpc/powerpc64/multiarch/stpncpy.c: New file:
	multiarch stpncpy for PPC64.
	* sysdeps/powerpc/powerpc64/multiarch/stpncpy-ppc64.c: New file
	* sysdeps/powerpc/powerpc64/multiarch/stpncpy-power7.S: New file

Signed-off-by: Vidya Ranganathan <vidya@linux.vnet.ibm.com>
---
 sysdeps/powerpc/powerpc64/multiarch/Makefile       |   3 +-
 .../powerpc/powerpc64/multiarch/ifunc-impl-list.c  |  16 +
 .../powerpc/powerpc64/multiarch/stpncpy-power7.S   |  44 +++
 .../powerpc/powerpc64/multiarch/stpncpy-ppc64.c    |  26 ++
 sysdeps/powerpc/powerpc64/multiarch/stpncpy.c      |  33 ++
 .../powerpc/powerpc64/multiarch/strncpy-power7.S   |  42 +++
 .../powerpc/powerpc64/multiarch/strncpy-ppc64.c    |  33 ++
 sysdeps/powerpc/powerpc64/multiarch/strncpy.c      |  35 +++
 sysdeps/powerpc/powerpc64/power7/stpncpy.S         |  24 ++
 sysdeps/powerpc/powerpc64/power7/strncpy.S         | 340 +++++++++++++++++++++
 10 files changed, 595 insertions(+), 1 deletion(-)
 create mode 100644 sysdeps/powerpc/powerpc64/multiarch/stpncpy-power7.S
 create mode 100644 sysdeps/powerpc/powerpc64/multiarch/stpncpy-ppc64.c
 create mode 100644 sysdeps/powerpc/powerpc64/multiarch/stpncpy.c
 create mode 100644 sysdeps/powerpc/powerpc64/multiarch/strncpy-power7.S
 create mode 100644 sysdeps/powerpc/powerpc64/multiarch/strncpy-ppc64.c
 create mode 100644 sysdeps/powerpc/powerpc64/multiarch/strncpy.c
 create mode 100644 sysdeps/powerpc/powerpc64/power7/stpncpy.S
 create mode 100644 sysdeps/powerpc/powerpc64/power7/strncpy.S

Comments

Adhemerval Zanella May 6, 2014, 4:55 p.m. UTC | #1
On 02-05-2014 16:11, vidya@linux.vnet.ibm.com wrote:
> From: Vidya Ranganathan <vidya@linux.vnet.ibm.com>
>
> The optimization is achieved by following techniques:
>    > data alignment [gain from aligned memory access on read/write]
>    > prefetch data [gain from cache misses by anticipating load]
>    > POWER7 gains performance with loop unrolling/unwinding
>       [gain by reduction of branch penalty].

Hi Vidya,

Thanks for the patch, I pushed upstream as f360f94a05570045be615649e9a411cefba2e210
with some modifications:

* sysdeps/powerpc/powerpc64/multiarch/strncpy.c header indentation was bogus

* I removed the pre-fetch instruction on strncpy.S for some reason:
  1. It didn't show performance difference in my tests
  2. The usage for r3 is wrong, it should be dcbtst since the memory location will
     be written.
  3. Also, on other string/memory operations it is used on loops with large sizes.
     Usually for few bytes the cost is not shown (as I saw) and you usage just 
     prefetch the first cache-line.

  If you find a new utilization that shows a better performance, please send a patch
  with results

* Added a comment saying the algorithms is using memset to zero pad the final bytes
  (different than default algorithm)

Patch
diff mbox

diff --git a/sysdeps/powerpc/powerpc64/multiarch/Makefile b/sysdeps/powerpc/powerpc64/multiarch/Makefile
index 8d367aa..35020a7 100644
--- a/sysdeps/powerpc/powerpc64/multiarch/Makefile
+++ b/sysdeps/powerpc/powerpc64/multiarch/Makefile
@@ -16,7 +16,8 @@  sysdep_routines += memcpy-power7 memcpy-a2 memcpy-power6 memcpy-cell \
 		   strcpy-power7 strcpy-ppc64 stpcpy-power7 stpcpy-ppc64 \
 		   strrchr-power7 strrchr-ppc64 strncat-power7 strncat-ppc64 \
 		   strspn-power7 strspn-ppc64 strcspn-power7 strcspn-ppc64 \
-		   strpbrk-power7 strpbrk-ppc64
+		   strpbrk-power7 strpbrk-ppc64 strncpy-power7 strncpy-ppc64 \
+		   stpncpy-power7 stpncpy-ppc64
 
 CFLAGS-strncase-power7.c += -mcpu=power7 -funroll-loops
 CFLAGS-strncase_l-power7.c += -mcpu=power7 -funroll-loops
diff --git a/sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c b/sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c
index 91fabb0..d8578fb 100644
--- a/sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c
+++ b/sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c
@@ -278,5 +278,21 @@  __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 	      IFUNC_IMPL_ADD (array, i, strpbrk, 1,
 			     __strpbrk_ppc))
 
+  /* Support sysdeps/powerpc/powerpc64/multiarch/strncpy.c.  */
+  IFUNC_IMPL (i, name, strncpy,
+	      IFUNC_IMPL_ADD (array, i, strncpy,
+			      hwcap & PPC_FEATURE_HAS_VSX,
+			      __strncpy_power7)
+	      IFUNC_IMPL_ADD (array, i, strncpy, 1,
+			     __strncpy_ppc))
+
+  /* Support sysdeps/powerpc/powerpc64/multiarch/stpncpy.c.  */
+  IFUNC_IMPL (i, name, stpncpy,
+	      IFUNC_IMPL_ADD (array, i, stpncpy,
+			      hwcap & PPC_FEATURE_HAS_VSX,
+			      __stpncpy_power7)
+	      IFUNC_IMPL_ADD (array, i, stpncpy, 1,
+			     __stpncpy_ppc))
+
   return i;
 }
diff --git a/sysdeps/powerpc/powerpc64/multiarch/stpncpy-power7.S b/sysdeps/powerpc/powerpc64/multiarch/stpncpy-power7.S
new file mode 100644
index 0000000..e29674f
--- /dev/null
+++ b/sysdeps/powerpc/powerpc64/multiarch/stpncpy-power7.S
@@ -0,0 +1,44 @@ 
+/* Optimized stpncpy implementation for POWER7.
+   Copyright (C) 2014 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+
+#define USE_AS_STPNCPY
+
+#undef EALIGN
+#define EALIGN(name, alignt, words)				\
+  .section ".text";						\
+  ENTRY_2(__stpncpy_power7)					\
+  .align ALIGNARG(alignt);					\
+  EALIGN_W_##words;						\
+  BODY_LABEL(__stpncpy_power7):					\
+  cfi_startproc;						\
+  LOCALENTRY(__stpncpy_power7)
+
+#undef END
+#define END(name)						\
+  cfi_endproc;							\
+  TRACEBACK(__stpncpy_power7)					\
+  END_2(__stpncpy_power7)
+
+#undef libc_hidden_builtin_def
+#define libc_hidden_builtin_def(name)
+
+#define MEMSET __memset_power7
+
+#include <sysdeps/powerpc/powerpc64/power7/stpncpy.S>
diff --git a/sysdeps/powerpc/powerpc64/multiarch/stpncpy-ppc64.c b/sysdeps/powerpc/powerpc64/multiarch/stpncpy-ppc64.c
new file mode 100644
index 0000000..74f47a7
--- /dev/null
+++ b/sysdeps/powerpc/powerpc64/multiarch/stpncpy-ppc64.c
@@ -0,0 +1,26 @@ 
+/* Default stpncpy implementation for PowerPC64.
+   Copyright (C) 2014 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#define STPNCPY __stpncpy_ppc
+#ifdef SHARED
+#undef libc_hidden_def
+#define libc_hidden_def(name) \
+  __hidden_ver1 (__stpncpy_ppc, __GI___stpncpy, __stpncpy_ppc);
+#endif
+
+#include <string/stpncpy.c>
diff --git a/sysdeps/powerpc/powerpc64/multiarch/stpncpy.c b/sysdeps/powerpc/powerpc64/multiarch/stpncpy.c
new file mode 100644
index 0000000..dbf8521
--- /dev/null
+++ b/sysdeps/powerpc/powerpc64/multiarch/stpncpy.c
@@ -0,0 +1,33 @@ 
+/* Multiple versions of stpncpy. PowerPC64 version.
+   Copyright (C) 2014 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef NOT_IN_libc
+# include <string.h>
+# include <shlib-compat.h>
+# include "init-arch.h"
+
+extern __typeof (__stpncpy) __stpncpy_ppc attribute_hidden;
+extern __typeof (__stpncpy) __stpncpy_power7 attribute_hidden;
+
+libc_ifunc (__stpncpy,
+            (hwcap & PPC_FEATURE_HAS_VSX)
+            ? __stpncpy_power7
+            : __stpncpy_ppc);
+
+weak_alias (__stpncpy, stpncpy)
+#endif
diff --git a/sysdeps/powerpc/powerpc64/multiarch/strncpy-power7.S b/sysdeps/powerpc/powerpc64/multiarch/strncpy-power7.S
new file mode 100644
index 0000000..be349f9
--- /dev/null
+++ b/sysdeps/powerpc/powerpc64/multiarch/strncpy-power7.S
@@ -0,0 +1,42 @@ 
+/* Optimized strncpy implementation for POWER7.
+   Copyright (C) 2014 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+
+#undef EALIGN
+#define EALIGN(name, alignt, words)				\
+  .section ".text";						\
+  ENTRY_2(__strncpy_power7)					\
+  .align ALIGNARG(alignt);					\
+  EALIGN_W_##words;						\
+  BODY_LABEL(__strncpy_power7):					\
+  cfi_startproc;						\
+  LOCALENTRY(__strncpy_power7)
+
+#undef END
+#define END(name)						\
+  cfi_endproc;							\
+  TRACEBACK(__strncpy_power7)					\
+  END_2(__strncpy_power7)
+
+#undef libc_hidden_builtin_def
+#define libc_hidden_builtin_def(name)
+
+#define MEMSET __memset_power7
+
+#include <sysdeps/powerpc/powerpc64/power7/strncpy.S>
diff --git a/sysdeps/powerpc/powerpc64/multiarch/strncpy-ppc64.c b/sysdeps/powerpc/powerpc64/multiarch/strncpy-ppc64.c
new file mode 100644
index 0000000..e3111d2
--- /dev/null
+++ b/sysdeps/powerpc/powerpc64/multiarch/strncpy-ppc64.c
@@ -0,0 +1,33 @@ 
+/* Copyright (C) 2014 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <string.h>
+
+#define STRNCPY __strncpy_ppc
+#undef weak_alias
+#define weak_alias(name, aliasname) \
+  extern __typeof (__strncpy_ppc) aliasname \
+    __attribute__ ((weak, alias ("__strncpy_ppc")));
+#if !defined(NOT_IN_libc) && defined(SHARED)
+# undef libc_hidden_builtin_def
+# define libc_hidden_builtin_def(name) \
+  __hidden_ver1(__strncpy_ppc, __GI_strncpy, __strncpy_ppc);
+#endif
+
+extern __typeof (strncpy) __strncpy_ppc attribute_hidden;
+
+#include <string/strncpy.c>
diff --git a/sysdeps/powerpc/powerpc64/multiarch/strncpy.c b/sysdeps/powerpc/powerpc64/multiarch/strncpy.c
new file mode 100644
index 0000000..818aba8
--- /dev/null
+++ b/sysdeps/powerpc/powerpc64/multiarch/strncpy.c
@@ -0,0 +1,35 @@ 
+/* Multiple versions of strncpy.
+ Copyright (C) 2014 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, see
+ <http://www.gnu.org/licenses/ >. */
+
+/* Define multiple versions only for definition in libc. */
+#ifndef NOT_IN_libc
+# include <string.h>
+# include <shlib-compat.h>
+# include "init-arch.h"
+
+extern __typeof (strncpy) __strncpy_ppc attribute_hidden;
+extern __typeof (strncpy) __strncpy_power7 attribute_hidden;
+
+/* Avoid DWARF definition DIE on ifunc symbol so that GDB can handle
+ ifunc symbol properly. */
+libc_ifunc (strncpy,
+            (hwcap & PPC_FEATURE_HAS_VSX)
+            ? __strncpy_power7
+            : __strncpy_ppc);
+
+#endif
diff --git a/sysdeps/powerpc/powerpc64/power7/stpncpy.S b/sysdeps/powerpc/powerpc64/power7/stpncpy.S
new file mode 100644
index 0000000..a539093
--- /dev/null
+++ b/sysdeps/powerpc/powerpc64/power7/stpncpy.S
@@ -0,0 +1,24 @@ 
+/* Optimized stpncpy implementation for PowerPC64/POWER7.
+   Copyright (C) 2014 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#define USE_AS_STPNCPY
+#include <sysdeps/powerpc/powerpc64/power7/strncpy.S>
+
+weak_alias (__stpncpy, stpncpy)
+libc_hidden_def (__stpncpy)
+libc_hidden_builtin_def (stpncpy)
diff --git a/sysdeps/powerpc/powerpc64/power7/strncpy.S b/sysdeps/powerpc/powerpc64/power7/strncpy.S
new file mode 100644
index 0000000..dd28088
--- /dev/null
+++ b/sysdeps/powerpc/powerpc64/power7/strncpy.S
@@ -0,0 +1,340 @@ 
+/* Copyright (C) 2014 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+
+/* Implements the functions
+
+   char * [r3] strncpy (char *dst [r3], const char *src [r4], size_t n [r5])
+
+   AND
+
+   char * [r3] stpncpy (char *dst [r3], const char *src [r4], size_t n [r5])
+
+   The algorithm is as follows:
+   > if src and dest are 8 byte aligned, perform double word copy
+     else
+   > copy byte by byte on unaligned addresses.
+
+   The aligned comparison are made using cmpb instructions.  */
+
+/* The focus on optimization for performance improvements are as follows:
+   1. data alignment [gain from aligned memory access on read/write]
+   2. prefetch data [gain from cache misses by anticipating load]
+   3. POWER7 gains performance with loop unrolling/unwinding
+      [gain by reduction of branch penalty].  */
+
+#ifdef USE_AS_STPNCPY
+# define FUNC_NAME __stpncpy
+#else
+# define FUNC_NAME strncpy
+#endif
+
+#define		FRAMESIZE	(FRAME_MIN_SIZE+32)
+
+#ifndef MEMSET
+/* For builds with no IFUNC support, local calls should be made to internal
+   GLIBC symbol (created by libc_hidden_builtin_def).  */
+# ifdef SHARED
+#  define MEMSET   __GI_memset
+# else
+#  define MEMSET   memset
+# endif
+#endif
+
+	.machine  power7
+EALIGN(FUNC_NAME, 4, 0)
+	CALL_MCOUNT 3
+
+	dcbt 0, r3		/* CPU pre-fetch dst to avoid cache miss  */
+	dcbt 0, r4		/* CPU pre-fetch src to avoid cache miss  */
+
+	mflr r0			/* load link register LR to r0  */
+	or r10, r3, r4		/* to verify source and destination  */
+	rldicl. r8, r10, 0, 61	/* is double word aligned .. ?  */
+
+	std r19, -8(r1)		/* save callers register , r19  */
+	std r18, -16(r1)	/* save callers register , r18  */
+	std r0, 16(r1)		/* store the link register  */
+	stdu r1, -FRAMESIZE(r1)	/* create the stack frame  */
+
+	mr r9, r3		/* save r3 into r9 for use  */
+	mr r18, r3		/* save r3 for retCode of strncpy  */
+	bne 0, L(byte_by_byte)
+
+
+	srdi r11, r5, 3		/* compute count for CTR ; count = n/8  */
+	cmpldi cr7, r11, 3	/* if count > 4 ; perform unrolling 4 times  */
+	ble 7, L(update1)
+
+	ld r10, 0(r4)		/* load doubleWord from src  */
+	cmpb r8, r10, r8	/* compare src with NULL ,we read just now  */
+	cmpdi cr7, r8, 0	/* if cmpb returned NULL ; we continue  */
+	bne cr7, L(update3)
+
+	std r10, 0(r3)		/* copy doubleword at offset=0  */
+	ld r10, 8(r4)		/* load next doubleword from offset=8  */
+	cmpb r8, r10, r8	/* compare src with NULL , we read just now  */
+	cmpdi cr7, r8, 0	/* if cmpb returned NULL ; we continue  */
+	bne 7,L(HopBy8)
+
+	addi r8, r11, -4
+	mr r7, r3
+	srdi r8, r8, 2
+	mr r6, r4
+	addi r8, r8, 1
+	li r12, 0
+	mtctr r8
+	b L(dwordCopy)
+
+	.p2align 4
+L(dWordUnroll):
+	std r8, 16(r9)
+	ld r8, 24(r4)		/* load dword,perform loop unrolling again  */
+	cmpb r10, r8, r10
+	cmpdi cr7, r10, 0
+	bne cr7, L(HopBy24)
+
+	std r8, 24(r7)		/* copy dword at offset=24  */
+	addi r9, r9, 32
+	addi r4, r4, 32
+	bdz  L(leftDwords)	/* continue with loop on counter  */
+
+	ld r3, 32(r6)
+	cmpb r8, r3, r10
+	cmpdi cr7, r8, 0
+	bne cr7, L(update2)
+
+	std r3, 32(r7)
+	ld r10, 40(r6)
+	cmpb r8, r10, r8
+	cmpdi cr7, r8, 0
+	bne cr7, L(HopBy40)
+
+	mr r6, r4		/* update values  */
+	mr r7, r9
+	mr r11, r0
+	mr r5, r19
+
+L(dwordCopy):
+	std r10, 8(r9)		/* copy dword at offset=8  */
+	addi r19, r5, -32
+	addi r0, r11, -4
+	ld r8, 16(r4)
+	cmpb r10, r8, r12
+	cmpdi cr7, r10, 0
+	beq cr7, L(dWordUnroll)
+
+	addi r9, r9, 16		/* increment dst by 16  */
+	addi r4, r4, 16		/* increment src by 16  */
+	addi r5, r5, -16	/* decrement length 'n' by 16  */
+	addi r0, r11, -2	/* decrement loop counter  */
+
+L(dWordUnrollOFF):
+	ld r10, 0(r4)		/* load first dword  */
+	li r8, 0		/* load mask  */
+	cmpb r8, r10, r8
+	cmpdi cr7, r8, 0
+	bne cr7, L(byte_by_byte)
+	mtctr r0
+	li r7, 0
+	b L(CopyDword)
+
+	.p2align 4
+L(loadDWordandCompare):
+	ld r10, 0(r4)
+	cmpb r8, r10, r7
+	cmpdi cr7, r8, 0
+	bne cr7, L(byte_by_byte)
+
+L(CopyDword):
+	addi r9, r9, 8
+	std r10, -8(r9)
+	addi r4, r4, 8
+	addi r5, r5, -8
+	bdnz L(loadDWordandCompare)
+
+L(byte_by_byte):
+	cmpldi cr7, r5, 3
+	ble cr7, L(verifyByte)
+	srdi r10, r5, 2
+	mr r19, r9
+	mtctr r10
+	b L(firstByteUnroll)
+
+	.p2align 4
+L(bytes_unroll):
+	lbz r10, 1(r4)		/* load byte from src  */
+	cmpdi cr7, r10, 0	/* compare for NULL  */
+	stb r10, 1(r19)		/* store byte to dst  */
+	beq cr7, L(updtDestComputeN2ndByte)
+
+	addi r4, r4, 4		/* advance src  */
+
+	lbz r10, -2(r4)		/* perform loop unrolling for byte r/w  */
+	cmpdi cr7, r10, 0
+	stb r10, 2(r19)
+	beq cr7, L(updtDestComputeN3rdByte)
+
+	lbz r10, -1(r4)		/* perform loop unrolling for byte r/w  */
+	addi r19, r19, 4
+	cmpdi cr7, r10, 0
+	stb r10, -1(r19)
+	beq cr7, L(ComputeNByte)
+
+	bdz L(update0)
+
+L(firstByteUnroll):
+	lbz r10, 0(r4)		/* perform loop unrolling for byte r/w  */
+	cmpdi cr7, 10, 0
+	stb r10, 0(r19)
+	bne cr7, L(bytes_unroll)
+	addi r19, r19, 1
+
+L(ComputeNByte):
+	subf r9, r19, r9	/* compute 'n'n bytes to fill  */
+	add r8, r9, r5
+
+L(zeroFill):
+	cmpdi cr7, r8, 0	/* compare if length is zero  */
+	beq cr7, L(update3return)
+
+	mr r3, r19		/* fill buffer with  */
+	li r4, 0		/* zero fill buffer  */
+	mr r5, r8		/* how many bytes to fill buffer with  */
+	bl MEMSET		/* call optimized memset  */
+	nop			/* trigger CPU activity  */
+
+L(update3return):
+#ifdef USE_AS_STPNCPY
+	addi r3, r19, -1	/* update return value  */
+#endif
+
+L(hop2return):
+#ifndef USE_AS_STPNCPY
+	mr r3, r18		/* set return value  */
+#endif
+	addi r1, r1, FRAMESIZE	/* restore stack pointer  */
+	ld r0, 16(r1)		/* read the saved link register  */
+	ld r18, -16(r1)		/* restore callers save register, r18  */
+	ld r19, -8(r1)		/* restore callers save register, r19  */
+	mtlr r0			/* branch to link register  */
+	blr			/* return  */
+
+	.p2align 4
+L(update0):
+	mr r9, r19
+
+	.p2align 4
+L(verifyByte):
+	rldicl. r8, r5, 0, 62
+#ifdef USE_AS_STPNCPY
+	mr r3, r9
+#endif
+	beq cr0, L(hop2return)
+	mtctr r8
+	addi r4, r4, -1
+	mr r19, r9
+	b L(oneBYone)
+
+	.p2align 4
+L(proceed):
+	bdz L(done)
+
+L(oneBYone):
+	lbzu r10, 1(r4)		/* copy byte  */
+	addi r19, r19, 1
+	addi r8, r8, -1
+	cmpdi cr7, r10, 0
+	stb r10, -1(r19)
+	bne cr7, L(proceed)
+	b L(zeroFill)
+
+	.p2align 4
+L(done):
+	addi r1, r1, FRAMESIZE	/* restore stack pointer  */
+#ifdef USE_AS_STPNCPY
+	mr r3, r19		/* set the return value  */
+#else
+	mr r3, r18		/* set the return value  */
+#endif
+	ld r0, 16(r1)		/* read the saved link register  */
+	ld r18, -16(r1)		/* restore callers save register, r18  */
+	ld r19, -8(r1)		/* restore callers save register, r19  */
+	mtlr r0			/* branch to link register  */
+	blr			/* return  */
+
+L(update1):
+	mr r0, r11
+	mr r19, r5
+
+	.p2align 4
+L(leftDwords):
+	cmpdi cr7, r0, 0
+	mr r5, r19
+	bne cr7, L(dWordUnrollOFF)
+	b L(byte_by_byte)
+
+	.p2align 4
+L(updtDestComputeN2ndByte):
+	addi r19, r19, 2	/* update dst by 2  */
+	subf r9, r19, r9	/* compute distance covered  */
+	add r8, r9, r5
+	b L(zeroFill)
+
+	.p2align 4
+L(updtDestComputeN3rdByte):
+	addi r19, r19, 3	/* update dst by 3  */
+	subf r9, r19, r9	/* compute distance covered  */
+	add r8, r9, r5
+	b L(zeroFill)
+
+	.p2align 4
+L(HopBy24):
+	addi r9, r9, 24		/* increment dst by 24  */
+	addi r4, r4, 24		/* increment src by 24  */
+	addi r5, r5, -24	/* decrement length 'n' by 24  */
+	addi r0, r11, -3	/* decrement loop counter  */
+	b L(dWordUnrollOFF)
+
+	.p2align 4
+L(update2):
+	mr r5, r19
+	b L(dWordUnrollOFF)
+
+	.p2align 4
+L(HopBy40):
+	addi r9, r7, 40		/* increment dst by 40  */
+	addi r4, r6, 40		/* increment src by 40  */
+	addi r5, r5, -40	/* decrement length 'n' by 40  */
+	addi r0, r11, -5	/* decrement loop counter  */
+	b L(dWordUnrollOFF)
+
+L(update3):
+	mr r0, r11
+	b L(dWordUnrollOFF)
+
+L(HopBy8):
+	addi r9, r3, 8		/* increment dst by 8  */
+	addi r4, r4, 8		/* increment src by 8  */
+	addi r5, r5, -8		/* decrement length 'n' by 8  */
+	addi r0, r11, -1	/* decrement loop counter  */
+	b L(dWordUnrollOFF)
+END(FUNC_NAME)
+#ifndef USE_AS_STPNCPY
+libc_hidden_builtin_def (strncpy)
+#endif