Module Name: src
Committed By: matt
Date: Tue Jan 15 08:52:27 UTC 2013
Added Files:
src/common/lib/libc/arch/arm/string: strrchr_arm.S
Log Message:
Add ARM optimized version of strrchr.
To generate a diff of this commit:
cvs rdiff -u -r0 -r1.1 src/common/lib/libc/arch/arm/string/strrchr_arm.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/strrchr_arm.S
diff -u /dev/null src/common/lib/libc/arch/arm/string/strrchr_arm.S:1.1
--- /dev/null Tue Jan 15 08:52:27 2013
+++ src/common/lib/libc/arch/arm/string/strrchr_arm.S Tue Jan 15 08:52:27 2013
@@ -0,0 +1,145 @@
+/*-
+ * 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: strrchr_arm.S,v 1.1 2013/01/15 08:52:27 matt Exp $")
+
+#ifdef __ARMEL__
+#define BYTE0 0x000000ff
+#define BYTE1 0x0000ff00
+#define BYTE2 0x00ff0000
+#define BYTE3 0xff000000
+#define lshi lsl
+#else
+#define BYTE0 0xff000000
+#define BYTE1 0x00ff0000
+#define BYTE2 0x0000ff00
+#define BYTE3 0x000000ff
+#define lshi lsr
+#endif
+
+ .text
+ENTRY(strrchr)
+ mov ip, r0 /* we use r0 at the return value */
+ mov r0, #0 /* return NULL by default */
+ and r2, r1, #0xff /* restrict to byte value */
+1: tst ip, #3 /* test for word alignment */
+ beq .Lpre_main_loop /* finally word aligned */
+ ldrb r3, [ip], #1 /* load a byte */
+ cmp r3, r2 /* did it match? */
+ subeq r0, ip, #1 /* yes, remember that it did */
+ teq r3, #0 /* was it NUL? */
+ bne 1b /* no, try next byte */
+ RET /* return */
+.Lpre_main_loop:
+ push {r4, r5} /* save some registers */
+#if defined(_ARM_ARCH_7)
+ movw r1, #0xfefe /* magic constant; 254 in each byte */
+ movt r1, #0xfefe /* magic constant; 254 in each byte */
+#elif defined(_ARM_ARCH_6)
+ mov r1, #0xfe /* put 254 in low byte */
+ orr r1, r1, r1, lsl #8 /* move to next byte */
+ orr r1, r1, r1, lsl #16 /* move to next halfword */
+#endif /* _ARM_ARCH_6 */
+ orr r2, r2, r2, lsl #8 /* move to next byte */
+ orr r2, r2, r2, lsl #16 /* move to next halfword */
+.Lmain_loop:
+ ldr r3, [ip], #4 /* load next word */
+#if defined(_ARM_ARCH_6)
+ /*
+ * Add 254 to each byte using the UQADD8 (unsigned saturating add 8)
+ * instruction. For every non-NUL byte, the result for that byte will
+ * become 255. For NUL, it will be 254. When we complement the
+ * result, if the result is non-0 then we must have encountered a NUL.
+ */
+ uqadd8 r4, r3, r1 /* NUL detection happens here */
+ usub8 r3, r3, r2 /* bias for char looked for? */
+ uqadd8 r5, r3, r1 /* char detection happens here */
+ and r3, r4, r5 /* merge results */
+ mvns r3, r3 /* is the complement non-0? */
+ beq .Lmain_loop /* no, then keep going */
+
+ mvns r5, r5 /* get we find any matching bytes? */
+ beq .Ldone /* no, then we hit the end, return */
+ mvns r4, r4 /* did we encounter a NUL? */
+ beq .Lfind_match /* no, find matching byte */
+ /*
+ * Copy the NUL bit to the following byte lanes. Then clear any match
+ * bits in those byte lanes to prevent false positives in those bytes.
+ */
+ movs r3, r4, lshi #8 /* shift up a byte */
+ orrnes r3, r3, r3, lshi #8 /* if non 0, copy up to next byte */
+ orrnes r3, r3, r3, lshi #8 /* if non 0, copy up to last byte */
+ bics r5, r5, r3 /* clear match bits */
+ beq .Ldone /* no remaining matches, we're done */
+.Lfind_match:
+#ifdef __ARMEL__
+ rev r5, r5 /* we want this in BE for the CLZ */
+#endif
+ /*
+ * If we have multiple matches, we want to the select the "last" match
+ * in the word which will be the lowest bit set.
+ */
+ sub r3, r5, #1 /* subtract 1 */
+ and r3, r3, r5 /* and with mask */
+ eor r5, r5, r3 /* only have the lowest bit set left */
+ clz r5, r5 /* count how many leading zeros */
+ add r0, ip, r5, lsr #3 /* divide that by 8 and add to count */
+ sub r0, r0, #4 /* compensate for the post-inc */
+ teq r4, #0 /* did we read any NULs? */
+ beq .Lmain_loop /* no, get next word */
+#else
+ /*
+ * No fancy shortcuts so just test each byte lane for a NUL.
+ * (other tests for NULs in a word take more instructions/cycles).
+ */
+ eor r4, r3, r2 /* xor .. */
+ tst r3, #BYTE0 /* is byte 0 a NUL? */
+ beq .Ldone /* yes, then we're done */
+ tst r4, #BYTE0 /* is byte 0 a match? */
+ subeq r0, ip, #4 /* yes, remember its location */
+ tst r3, #BYTE1 /* is byte 1 a NUL? */
+ beq .Ldone /* yes, then we're done */
+ tst r4, #BYTE1 /* is byte 1 a match? */
+ subeq r0, ip, #3 /* yes, remember its location */
+ tst r3, #BYTE2 /* is byte 2 a NUL? */
+ beq .Ldone /* yes, then we're done */
+ tst r4, #BYTE2 /* is byte 2 a match? */
+ subeq r0, ip, #2 /* yes, remember its location */
+ tst r3, #BYTE3 /* is byte 3 a NUL? */
+ beq .Ldone /* yes, then we're done */
+ tst r4, #BYTE3 /* is byte 3 a match? */
+ subeq r0, ip, #1 /* yes, remember its location */
+ b .Lmain_loop
+#endif /* _ARM_ARCH_6 */
+.Ldone:
+ pop {r4, r5}
+ RET
+END(strrchr)
