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/*-
* 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 1.6 2013/08/25 06:15:06 matt Exp $")
#ifdef __ARMEL__
#define BYTE0 0x000000ff
#define BYTE1 0x0000ff00
#define BYTE2 0x00ff0000
#define BYTE3 0xff000000
#define lshi lsl
#define lshis lsls
#else
#define BYTE0 0xff000000
#define BYTE1 0x00ff0000
#define BYTE2 0x0000ff00
#define BYTE3 0x000000ff
#define lshi lsr
#define lshis lsrs
#endif
ENTRY(strrchr)
ands r2, r1, #0xff /* is the byte value NUL? */
bne 1f /* no, do it the hard way */
push {r0, lr} /* save pointer and return addr */
bl PLT_SYM(strlen) /* get length */
pop {r1, r2} /* restore pointer / return addr */
adds r0, r0, r1 /* add pointer to length */
RETr(r2) /* return */
1: mov r1, r0 /* we use r0 at the return value */
movs r0, #0 /* return NULL by default */
2: tst r1, #3 /* test for word alignment */
beq .Lpre_main_loop /* finally word aligned */
ldrb r3, [r1], #1 /* load a byte */
cmp r3, r2 /* did it match? */
#ifdef __thumb__
it eq
#endif
subeq r0, r1, #1 /* yes, remember that it did */
cmp r3, #0 /* was it NUL? */
bne 2b /* no, try next byte */
RET /* return */
.Lpre_main_loop:
push {r4, r5} /* save some registers */
#if defined(_ARM_ARCH_7)
movw ip, #0xfefe /* magic constant; 254 in each byte */
movt ip, #0xfefe /* magic constant; 254 in each byte */
#elif defined(_ARM_ARCH_6)
mov ip, #0xfe /* put 254 in low byte */
orr ip, ip, ip, lsl #8 /* move to next byte */
orr ip, ip, ip, 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, [r1], #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, ip /* NUL detection happens here */
usub8 r3, r3, r2 /* bias for char looked for? */
uqadd8 r5, r3, ip /* char detection happens here */
ands 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.
*/
bics r5, r5, r4 /* clear any NUL match bits */
beq .Ldone /* no remaining matches, we're done */
lshis r3, r4, #8 /* shift up a byte */
#ifdef __thumb__
itt ne
#endif
orrsne r3, r3, r3, lshi #8 /* if non 0, copy up to next byte */
orrsne 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.
*/
subs r3, r5, #1 /* subtract 1 */
ands r3, r3, r5 /* and with mask */
eors r5, r5, r3 /* only have the lowest bit set left */
clz r5, r5 /* count how many leading zeros */
add r0, r1, r5, lsr #3 /* divide that by 8 and add to count */
subs r0, r0, #4 /* compensate for the post-inc */
cmp 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, r1, #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, r1, #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, r1, #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, r1, #1 /* yes, remember its location */
b .Lmain_loop
#endif /* _ARM_ARCH_6 */
.Ldone:
pop {r4, r5}
RET
END(strrchr)
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