[src/trunk]: src/common/lib/libc/arch/arm/string Add a simplier version of me...

[matt <matt%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/918411e17f08
branches:  trunk
changeset: 783791:918411e17f08
user:      matt <matt%NetBSD.org@localhost>
date:      Tue Jan 08 20:15:00 2013 +0000

description:
Add a simplier version of memset which is less than 1/2 the size of the
current one.  On a Cortex-A9, this is about 15%-30% faster than the current
libc version.  This is not a trivial implementation since that was an order
magnitude slower than the existing libc version.

diffstat:

 common/lib/libc/arch/arm/string/memset_naive.S |  86 ++++++++++++++++++++++++++
 1 files changed, 86 insertions(+), 0 deletions(-)

diffs (90 lines):

diff -r b472a0f0b660 -r 918411e17f08 common/lib/libc/arch/arm/string/memset_naive.S
--- /dev/null   Thu Jan 01 00:00:00 1970 +0000
+++ b/common/lib/libc/arch/arm/string/memset_naive.S    Tue Jan 08 20:15:00 2013 +0000
@@ -0,0 +1,86 @@
+/*-
+ * Copyright (c) 2013 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * This code is derived from software contributed to The NetBSD Foundation
+ * by Matt Thomas of 3am Software Foundry.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <machine/asm.h>
+
+RCSID("$NetBSD: memset_naive.S,v 1.1 2013/01/08 20:15:00 matt Exp $")
+
+/*
+ * This isn't quite as simple/short as it could be but the truly trivial
+ * memset was an order of magnitude slower than this.
+ */
+
+ENTRY(memset)
+/* LINTSTUB: void *memset(void *, int, size_t) */
+       mov     ip, r0                  /* need to preserve r0 */
+       cmp     r2, #10                 /* 10 bytes or less? */
+       ble     .Lbyte_by_byte          /*    yes, bytewise is faster */
+       ands    r3, r1, #0xff           /* we are dealing with bytes */
+       orrne   r3, r3, r3, lsl #8      /* move value into 2nd byte lane */
+       orrne   r3, r3, r3, lsl #16     /* move value into all byte lanes */
+       mov     r1, r2                  /* move count */
+       ands    r2, ip, #7              /* are we dword aligned? */
+       beq     1f                      /*   yes we are */
+       rsb     r2, r2, #8              /* how many bytes until aligned? */
+       sub     r1, r1, r2              /* subtract from count */
+       tst     ip, #1                  /* halfword aligned? */
+       strneb  r3, [ip], #1            /*   nope, write a byte */
+       tst     ip, #2                  /* word aligned? */
+       strneh  r3, [ip], #2            /*   nope, write a halfword */
+       tst     ip, #4                  /* dword aligned? */
+       strne   r3, [ip], #4            /*   nope, write a word */
+       /*
+        * At this point, we are dword aligned.
+        */
+1:     mov     r2, r3                  /* duplicate fill value */
+2:     subs    r1, r1, #16             /* can we write 16 bytes? */
+       stmgeia ip!, {r2,r3}            /*   yes, write the first 8 of them */
+       stmgeia ip!, {r2,r3}            /*   yes, write the second 8 of them */
+       bgt     2b                      /* more left to fill */
+       RETc(eq)                        /*   no, return */
+       /*
+        * Our count went negative but the bits below 16 haven't changed.
+        * So we are effectively testing modulo 16.
+        */
+       tst     r1, #8                  /* can we write at least 8 bytes? */
+       stmneia ip!, {r2,r3}            /*   so do it */
+       tst     r1, #4                  /* can we write at least 4 bytes? */
+       strne   r3, [ip], #4            /*   so do it */
+       tst     r1, #2                  /* can we write at least 2 bytes? */
+       strneh  r3, [ip], #2            /*   so do it */
+       tst     r1, #1                  /* can we write 1 bytes? */
+       strneb  r3, [ip], #1            /*   so do it */
+       RET                             /* return */
+
+.Lbyte_by_byte:
+       subs    r2, r2, #1              /* can we write a byte? */
+       RETc(lt)                        /*   no, return */
+       strb    r3, [ip], #1            /* write a byte */
+       b       .Lbyte_by_byte          /* do next byte */
+END(memset)