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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 shift x4
#define data q0
#define vdata v0
#define vhas_nul v1
#define vend v2
#define dend d2
/* 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 trailing zeros identifies
exactly which byte matched. */
ENTRY (STRLEN)
PTR_ARG (0)
bic src, srcin, 15
ld1 {vdata.16b}, [src]
cmeq vhas_nul.16b, vdata.16b, 0
lsl shift, srcin, 2
shrn vend.8b, vhas_nul.8h, 4 /* 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)
shrn vend.8b, vhas_nul.8h, 4 /* 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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