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/* strchr - find a character in a string
Copyright (C) 2014-2024 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.
*/
#define srcin x0
#define chrin w1
#define result x0
#define src x2
#define tmp1 x1
#define tmp2 x3
#define vrepchr v0
#define vdata v1
#define qdata q1
#define vhas_nul v2
#define vhas_chr v3
#define vrepmask v4
#define vend v5
#define dend d5
/* Core algorithm.
For each 16-byte chunk we calculate a 64-bit syndrome value with four bits
per byte. Bits 0-1 are set if the relevant byte matched the requested
character, bits 2-3 are set if the byte is NUL or matched. Count trailing
zeroes gives the position of the matching byte if it is a multiple of 4.
If it is not a multiple of 4, there was no match. */
ENTRY (strchr)
PTR_ARG (0)
bic src, srcin, 15
dup vrepchr.16b, chrin
ld1 {vdata.16b}, [src]
movi vrepmask.16b, 0x33
cmeq vhas_nul.16b, vdata.16b, 0
cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
bit vhas_nul.16b, vhas_chr.16b, vrepmask.16b
lsl tmp2, srcin, 2
shrn vend.8b, vhas_nul.8h, 4 /* 128->64 */
fmov tmp1, dend
lsr tmp1, tmp1, tmp2
cbz tmp1, L(loop)
rbit tmp1, tmp1
clz tmp1, tmp1
/* Tmp1 is an even multiple of 2 if the target character was
found first. Otherwise we've found the end of string. */
tst tmp1, 2
add result, srcin, tmp1, lsr 2
csel result, result, xzr, eq
ret
.p2align 4
L(loop):
ldr qdata, [src, 16]
cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
cmhs vhas_nul.16b, vhas_chr.16b, vdata.16b
umaxp vend.16b, vhas_nul.16b, vhas_nul.16b
fmov tmp1, dend
cbnz tmp1, L(end)
ldr qdata, [src, 32]!
cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
cmhs vhas_nul.16b, vhas_chr.16b, vdata.16b
umaxp vend.16b, vhas_nul.16b, vhas_nul.16b
fmov tmp1, dend
cbz tmp1, L(loop)
sub src, src, 16
L(end):
#ifdef __AARCH64EB__
bif vhas_nul.16b, vhas_chr.16b, vrepmask.16b
shrn vend.8b, vhas_nul.8h, 4 /* 128->64 */
fmov tmp1, dend
#else
bit vhas_nul.16b, vhas_chr.16b, vrepmask.16b
shrn vend.8b, vhas_nul.8h, 4 /* 128->64 */
fmov tmp1, dend
rbit tmp1, tmp1
#endif
add src, src, 16
clz tmp1, tmp1
/* Tmp1 is a multiple of 4 if the target character was found. */
tst tmp1, 2
add result, src, tmp1, lsr 2
csel result, result, xzr, eq
ret
END (strchr)
libc_hidden_builtin_def (strchr)
weak_alias (strchr, index)
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