Module Name: src
Committed By: matt
Date: Tue Jan 8 20:15:00 UTC 2013
Added Files:
src/common/lib/libc/arch/arm/string: memset_naive.S
Log Message:
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.
To generate a diff of this commit:
cvs rdiff -u -r0 -r1.1 src/common/lib/libc/arch/arm/string/memset_naive.S
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Added files:
Index: src/common/lib/libc/arch/arm/string/memset_naive.S
diff -u /dev/null src/common/lib/libc/arch/arm/string/memset_naive.S:1.1
--- /dev/null Tue Jan 8 20:15:00 2013
+++ src/common/lib/libc/arch/arm/string/memset_naive.S Tue Jan 8 20:15:00 2013
@@ -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)
