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/* memchr - find a character in a memory zone
Copyright (C) 2015-2024 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.
*/
#ifndef MEMCHR
# define MEMCHR __memchr
#endif
#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 vrepchr v0
#define qdata q1
#define vdata v1
#define vhas_chr v2
#define vend v3
#define dend d3
/*
Core algorithm:
For each 16-byte chunk we calculate a 64-bit nibble mask value with four bits
per byte. We take 4 bits of every comparison byte with shift right and narrow
by 4 instruction. Since the bits in the nibble mask reflect the order in
which things occur in the original string, counting leading zeros identifies
exactly which byte matched. */
ENTRY (MEMCHR)
PTR_ARG (0)
SIZE_ARG (2)
bic src, srcin, 15
cbz cntin, L(nomatch)
ld1 {vdata.16b}, [src]
dup vrepchr.16b, chrin
cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
lsl shift, srcin, 2
shrn vend.8b, vhas_chr.8h, 4 /* 128->64 */
fmov synd, dend
lsr synd, synd, shift
cbz synd, L(start_loop)
rbit synd, synd
clz synd, synd
cmp cntin, synd, lsr 2
add result, srcin, synd, lsr 2
csel result, result, xzr, hi
ret
.p2align 3
L(start_loop):
sub tmp, src, srcin
add tmp, tmp, 17
subs cntrem, cntin, tmp
b.lo L(nomatch)
/* Make sure that it won't overread by a 16-byte chunk */
tbz cntrem, 4, L(loop32_2)
sub src, src, 16
.p2align 4
L(loop32):
ldr qdata, [src, 32]!
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]
cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
subs cntrem, cntrem, 32
b.lo L(end_2)
umaxp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
fmov synd, dend
cbz synd, L(loop32)
L(end_2):
add src, src, 16
L(end):
shrn vend.8b, vhas_chr.8h, 4 /* 128->64 */
sub cntrem, src, srcin
fmov synd, dend
sub cntrem, cntin, cntrem
#ifndef __AARCH64EB__
rbit synd, synd
#endif
clz synd, synd
cmp cntrem, synd, lsr 2
add result, src, synd, lsr 2
csel result, result, xzr, hi
ret
L(nomatch):
mov result, 0
ret
END (MEMCHR)
weak_alias (MEMCHR, memchr)
libc_hidden_builtin_def (memchr)
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