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[PATCH 21/26] arm: Implement armv6t2 optimized strcpy
- From: Richard Henderson <rth at twiddle dot net>
- To: libc-ports at sourceware dot org
- Cc: Joseph Myers <joseph at codesourcery dot com>
- Date: Tue, 26 Feb 2013 19:16:21 -0800
- Subject: [PATCH 21/26] arm: Implement armv6t2 optimized strcpy
- References: <1361934986-17018-1-git-send-email-rth@twiddle.net>
Four times faster than the byte-by-byte default version.
---
* sysdeps/arm/armv6t2/strcpy.S: New file.
* sysdeps/arm/armv6t2/stpcpy.S: New file.
---
ports/sysdeps/arm/armv6t2/stpcpy.S | 1 +
ports/sysdeps/arm/armv6t2/strcpy.S | 213 +++++++++++++++++++++++++++++++++++++
2 files changed, 214 insertions(+)
create mode 100644 ports/sysdeps/arm/armv6t2/stpcpy.S
create mode 100644 ports/sysdeps/arm/armv6t2/strcpy.S
diff --git a/ports/sysdeps/arm/armv6t2/stpcpy.S b/ports/sysdeps/arm/armv6t2/stpcpy.S
new file mode 100644
index 0000000..21a4f38
--- /dev/null
+++ b/ports/sysdeps/arm/armv6t2/stpcpy.S
@@ -0,0 +1 @@
+/* Defined in strcpy.S. */
diff --git a/ports/sysdeps/arm/armv6t2/strcpy.S b/ports/sysdeps/arm/armv6t2/strcpy.S
new file mode 100644
index 0000000..a0e3bcc
--- /dev/null
+++ b/ports/sysdeps/arm/armv6t2/strcpy.S
@@ -0,0 +1,213 @@
+/* Copyright (C) 2013 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>
+
+/* Endian independent macros for shifting bytes within registers. */
+#ifdef __ARMEB__
+#define lsh_gt lsr
+#define lsh_ls lsl
+#else
+#define lsh_gt lsl
+#define lsh_ls lsr
+#endif
+
+#ifndef USE_AS_STPCPY
+# define STRCPY strcpy
+#endif
+
+ .syntax unified
+ .text
+
+ENTRY(__stpcpy)
+ @ Signal stpcpy with NULL in IP.
+ s(mov) ip, #0
+ b 0f
+END(__stpcpy)
+
+weak_alias (__stpcpy, stpcpy)
+libc_hidden_def (__stpcpy)
+libc_hidden_builtin_def (stpcpy)
+
+ENTRY(strcpy)
+ @ Signal strcpy with DEST in IP.
+ mov ip, r0
+0:
+ @ To cater to long strings, we want 8 byte alignment in the source.
+ @ To cater to small strings, we don't want to start that right away.
+ @ Loop up to 16 times, less whatever it takes to reach alignment.
+ and r3, r1, #7
+ rsb r3, r3, #16
+
+ @ Loop until we find ...
+1: ldrb r2, [r1], #1
+ subs r3, r3, #1 @ ... the alignment point
+ strb r2, [r0], #1
+ it ne
+ cmpne r2, #0 @ ... or EOS
+ bne 1b
+
+ @ Disambiguate the exit possibilites above
+ cmp r2, #0 @ Found EOS
+ beq .Lreturn
+
+ @ Load the next two words asap
+ ldrd r2, r3, [r1], #8
+
+ @ For longer strings, we actaully need a stack frame.
+ push { r4, r5, r6, r7 }
+ cfi_adjust_cfa_offset (16)
+ cfi_rel_offset (r4, 0)
+ cfi_rel_offset (r5, 4)
+ cfi_rel_offset (r6, 8)
+ cfi_rel_offset (r7, 12)
+
+ @ Adding (unsigned saturating) 0xfe means result of 0xfe for any byte
+ @ that was originally zero and 0xff otherwise. Therefore we consider
+ @ the lsb of each byte the "found" bit, with 0 for a match.
+ movw r7, #0xfefe
+ tst r0, #3 @ Test alignment of DEST
+ movt r7, #0xfefe
+ bne .Lunaligned
+
+ @ So now source (r1) is aligned to 8, and dest (r0) is aligned to 4.
+ @ Loop, reading 8 bytes at a time, searching for EOS.
+ .balign 16
+2: uqadd8 r4, r2, r7 @ Find EOS
+ uqadd8 r5, r3, r7
+ pld [r1, #256]
+ mvns r4, r4 @ EOS in first word?
+
+ pld [r0, #256]
+ bne 3f
+ str r2, [r0], #4
+ mvns r5, r5 @ EOS in second word?
+
+ bne 4f
+ str r3, [r0], #4
+ ldrd r2, r3, [r1], #8
+ b 2b
+
+3: s(sub) r1, r1, #4 @ backup to first word
+4: s(sub) r1, r1, #4 @ backup to second word
+
+ @ ... then finish up any tail a byte at a time.
+ @ Note that we generally back up and re-read source bytes,
+ @ but we'll not re-write dest bytes.
+.Lbyte_loop:
+ ldrb r2, [r1], #1
+ cmp r2, #0
+ strb r2, [r0], #1
+ bne .Lbyte_loop
+
+ pop { r4, r5, r6, r7 }
+ cfi_remember_state
+ cfi_adjust_cfa_offset (-16)
+ cfi_restore (r4)
+ cfi_restore (r5)
+ cfi_restore (r6)
+ cfi_restore (r7)
+
+.Lreturn:
+ cmp ip, #0 @ Was this strcpy or strcpy?
+ ite eq
+ subeq r0, r0, #1 @ stpcpy: undo post-inc from store
+ movne r0, ip @ strcpy: return original dest
+ bx lr
+
+.Lunaligned:
+ cfi_restore_state
+ @ Here, source is aligned to 8, but the destination is not word
+ @ aligned. Therefore we have to shift the data in order to be
+ @ able to perform aligned word stores.
+
+ @ Find out which misalignment we're dealing with.
+ tst r0, #1
+ beq .Lunaligned2
+ tst r0, #2
+ bne .Lunaligned3
+ @ Fallthru to .Lunaligned1.
+
+.macro unaligned_copy unalign
+ @ Prologue to unaligned loop. Seed shifted non-zero bytes.
+ uqadd8 r4, r2, r7 @ Find EOS
+ uqadd8 r5, r3, r7
+ mvns r4, r4 @ EOS in first word?
+ it ne
+ subne r1, r1, #8
+ bne .Lbyte_loop
+#ifdef __ARMEB__
+ rev r2, r2 @ Byte stores below need LE data
+#endif
+ @ Store a few bytes from the first word.
+ @ At the same time we align r0 and shift out bytes from r2.
+.rept 4-\unalign
+ strb r2, [r0], #1
+ s(lsr) r2, r2, #8
+.endr
+#ifdef __ARMEB__
+ rev r2, r2 @ Undo previous rev
+#endif
+ @ Rotated unaligned copy loop. The tail of the prologue is
+ @ shared with the loop itself.
+ .balign 8
+1: mvns r5, r5 @ EOS in second word?
+ bne 4f
+ @ Combine first and second words
+ orr r2, r2, r3, lsh_gt #(\unalign*8)
+ @ Save leftover bytes from the two words
+ lsh_ls r6, r3, #((4-\unalign)*8)
+ str r2, [r0], #4
+ @ The "real" start of the unaligned copy loop.
+ ldrd r2, r3, [r1], #8 @ Load 8 more bytes
+ uqadd8 r4, r2, r7 @ Find EOS
+ pld [r1, #256]
+ uqadd8 r5, r3, r7
+ pld [r0, #256]
+ mvns r4, r4 @ EOS in first word?
+ bne 3f
+ @ Combine the leftover and the first word
+ orr r6, r6, r2, lsh_gt #(\unalign*8)
+ @ Discard used bytes from the first word.
+ lsh_ls r2, r2, #((4-\unalign)*8)
+ str r6, [r0], #4
+ b 1b
+ @ Found EOS in one of the words; adjust backward
+3: s(sub) r1, r1, #4
+ mov r2, r6
+4: s(sub) r1, r1, #4
+ @ And store the remaining bytes from the leftover
+#ifdef __ARMEB__
+ rev r2, r2
+#endif
+.rept \unalign
+ strb r2, [r0], #1
+ s(lsr) r2, r2, #8
+.endr
+ b .Lbyte_loop
+.endm
+
+.Lunaligned1:
+ unaligned_copy 1
+.Lunaligned2:
+ unaligned_copy 2
+.Lunaligned3:
+ unaligned_copy 3
+
+END(STRCPY)
+
+libc_hidden_builtin_def (strcpy)
--
1.8.1.2