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/* Copyright (C) 2012-2020 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.
*/
#ifndef STRLEN
# define STRLEN __strlen
#endif
#define srcin x0
#define result x0
#define src x1
#define synd x2
#define tmp x3
#define wtmp w3
#define shift x4
#define data q0
#define vdata v0
#define vhas_nul v1
#define vrepmask v2
#define vend v3
#define dend d3
/* 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 (STRLEN)
DELOUSE (0)
DELOUSE (1)
bic src, srcin, 15
mov wtmp, 0xf00f
ld1 {vdata.16b}, [src]
dup vrepmask.8h, wtmp
cmeq vhas_nul.16b, vdata.16b, 0
lsl shift, srcin, 2
and vhas_nul.16b, vhas_nul.16b, vrepmask.16b
addp vend.16b, vhas_nul.16b, vhas_nul.16b /* 128->64 */
fmov synd, dend
lsr synd, synd, shift
cbz synd, L(loop)
rbit synd, synd
clz result, synd
lsr result, result, 2
ret
.p2align 5
L(loop):
ldr data, [src, 16]!
cmeq vhas_nul.16b, vdata.16b, 0
umaxp vend.16b, vhas_nul.16b, vhas_nul.16b
fmov synd, dend
cbz synd, L(loop)
and vhas_nul.16b, vhas_nul.16b, vrepmask.16b
addp vend.16b, vhas_nul.16b, vhas_nul.16b /* 128->64 */
sub result, src, srcin
fmov synd, dend
#ifndef __AARCH64EB__
rbit synd, synd
#endif
clz tmp, synd
add result, result, tmp, lsr 2
ret
END (STRLEN)
weak_alias (STRLEN, strlen)
libc_hidden_builtin_def (strlen)
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