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/* memrchr - find the last occurrence of a byte in a memory block
Copyright (C) 2015-2020 Free Software Foundation, Inc.
This file is part of the GNU C Library.
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>
/* Assumptions:
*
* ARMv8-a, AArch64, Advanced SIMD.
* MTE compatible.
*/
/* Arguments and results. */
#define srcin x0
#define chrin w1
#define cntin x2
#define result x0
#define src x3
#define cntrem x4
#define synd x5
#define shift x6
#define tmp x7
#define wtmp w7
#define end x8
#define endm1 x9
#define vrepchr v0
#define qdata q1
#define vdata v1
#define vhas_chr v2
#define vrepmask v3
#define vend v4
#define dend d4
/*
Core algorithm:
For each 16-byte chunk we calculate a 64-bit syndrome value with four bits
per byte. For even bytes, bits 0-3 are set if the relevant byte matched the
requested character or the byte is NUL. Bits 4-7 must be zero. Bits 4-7 are
set likewise for odd bytes so that adjacent bytes can be merged. Since the
bits in the syndrome reflect the order in which things occur in the original
string, counting trailing zeros identifies exactly which byte matched. */
ENTRY (__memrchr)
PTR_ARG (0)
SIZE_ARG (2)
add end, srcin, cntin
sub endm1, end, 1
bic src, endm1, 15
cbz cntin, L(nomatch)
ld1 {vdata.16b}, [src]
dup vrepchr.16b, chrin
mov wtmp, 0xf00f
dup vrepmask.8h, wtmp
cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
neg shift, end, lsl 2
and vhas_chr.16b, vhas_chr.16b, vrepmask.16b
addp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
fmov synd, dend
lsl synd, synd, shift
cbz synd, L(start_loop)
clz synd, synd
sub result, endm1, synd, lsr 2
cmp cntin, synd, lsr 2
csel result, result, xzr, hi
ret
L(start_loop):
sub tmp, end, src
subs cntrem, cntin, tmp
b.ls L(nomatch)
/* Make sure that it won't overread by a 16-byte chunk */
add tmp, cntrem, 15
tbnz tmp, 4, L(loop32_2)
.p2align 4
L(loop32):
ldr qdata, [src, -16]!
cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
umaxp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
fmov synd, dend
cbnz synd, L(end)
L(loop32_2):
ldr qdata, [src, -16]!
subs cntrem, cntrem, 32
cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
b.ls L(end)
umaxp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
fmov synd, dend
cbz synd, L(loop32)
L(end):
and vhas_chr.16b, vhas_chr.16b, vrepmask.16b
addp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
fmov synd, dend
add tmp, src, 15
#ifdef __AARCH64EB__
rbit synd, synd
#endif
clz synd, synd
sub tmp, tmp, synd, lsr 2
cmp tmp, srcin
csel result, tmp, xzr, hs
ret
L(nomatch):
mov result, 0
ret
END (__memrchr)
weak_alias (__memrchr, memrchr)
libc_hidden_builtin_def (memrchr)
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