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/* Copyright (C) 2011-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Code contributed by Dave Gilbert <david.gilbert@linaro.org>
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
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
@ This memchr routine is optimised on a Cortex-A9 and should work on all ARMv7
@ and ARMv6T2 processors. It has a fast path for short sizes, and has an
@ optimised path for large data sets; the worst case is finding the match early
@ in a large data set.
@ Note: The use of cbz/cbnz means it's Thumb only
@ 2011-07-15 david.gilbert@linaro.org
@ Copy from Cortex strings release 21 and change license
@ http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/view/head:/src/linaro-a9/memchr.S
@ Change function declarations/entry/exit
@ 2011-12-01 david.gilbert@linaro.org
@ Add some fixes from comments received (including use of ldrd instead ldm)
@ 2011-12-07 david.gilbert@linaro.org
@ Removed cbz from align loop - can't be taken
@ this lets us check a flag in a 00/ff byte easily in either endianness
#ifdef __ARMEB__
#define CHARTSTMASK(c) 1<<(31-(c*8))
#else
#define CHARTSTMASK(c) 1<<(c*8)
#endif
.syntax unified
.text
.thumb
.thumb_func
.global memchr
.type memchr,%function
ENTRY(memchr)
@ r0 = start of memory to scan
@ r1 = character to look for
@ r2 = length
@ returns r0 = pointer to character or NULL if not found
and r1,r1,#0xff @ Don't think we can trust the caller to actually pass a char
cmp r2,#16 @ If it's short don't bother with anything clever
blt 20f
tst r0, #7 @ If it's already aligned skip the next bit
beq 10f
@ Work up to an aligned point
5:
ldrb r3, [r0],#1
subs r2, r2, #1
cmp r3, r1
beq 50f @ If it matches exit found
tst r0, #7
bne 5b @ If not aligned yet then do next byte
10:
@ At this point, we are aligned, we know we have at least 8 bytes to work with
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)
cfi_remember_state
orr r1, r1, r1, lsl #8 @ expand the match word across to all bytes
orr r1, r1, r1, lsl #16
bic r6, r2, #7 @ Number of double words to work with * 8
mvns r7, #0 @ all F's
movs r3, #0
15:
ldrd r4,r5, [r0],#8
subs r6, r6, #8
eor r4,r4, r1 @ Get it so that r4,r5 have 00's where the bytes match the target
eor r5,r5, r1
uadd8 r4, r4, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0
sel r4, r3, r7 @ bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
uadd8 r5, r5, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0
sel r5, r4, r7 @ chained....bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
cbnz r5, 60f
bne 15b @ (Flags from the subs above) If not run out of bytes then go around again
pop {r4,r5,r6,r7}
cfi_adjust_cfa_offset (-16)
cfi_restore (r4)
cfi_restore (r5)
cfi_restore (r6)
cfi_restore (r7)
and r1,r1,#0xff @ Get r1 back to a single character from the expansion above
and r2,r2,#7 @ Leave the count remaining as the number after the double words have been done
20:
cbz r2, 40f @ 0 length or hit the end already then not found
21: @ Post aligned section, or just a short call
ldrb r3,[r0],#1
subs r2,r2,#1
eor r3,r3,r1 @ r3 = 0 if match - doesn't break flags from sub
cbz r3, 50f
bne 21b @ on r2 flags
40:
movs r0,#0 @ not found
DO_RET(lr)
50:
subs r0,r0,#1 @ found
DO_RET(lr)
60: @ We're here because the fast path found a hit - now we have to track down exactly which word it was
@ r0 points to the start of the double word after the one that was tested
@ r4 has the 00/ff pattern for the first word, r5 has the chained value
cfi_restore_state
cmp r4, #0
itte eq
moveq r4, r5 @ the end is in the 2nd word
subeq r0,r0,#3 @ Points to 2nd byte of 2nd word
subne r0,r0,#7 @ or 2nd byte of 1st word
@ r0 currently points to the 2nd byte of the word containing the hit
tst r4, # CHARTSTMASK(0) @ 1st character
bne 61f
adds r0,r0,#1
tst r4, # CHARTSTMASK(1) @ 2nd character
ittt eq
addeq r0,r0,#1
tsteq r4, # (3<<15) @ 2nd & 3rd character
@ If not the 3rd must be the last one
addeq r0,r0,#1
61:
pop {r4,r5,r6,r7}
cfi_adjust_cfa_offset (-16)
cfi_restore (r4)
cfi_restore (r5)
cfi_restore (r6)
cfi_restore (r7)
subs r0,r0,#1
DO_RET(lr)
END(memchr)
libc_hidden_builtin_def (memchr)
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