mirror of
https://sourceware.org/git/glibc.git
synced 2024-12-02 01:40:07 +00:00
03c8ce5000
Optimize strlen by unrolling the main loop. Large strings are 64% faster on modern CPUs. Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
94 lines
2.2 KiB
ArmAsm
94 lines
2.2 KiB
ArmAsm
/* Copyright (C) 2012-2023 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:
|
|
Process the string in 16-byte aligned chunks. Compute a 64-bit mask with
|
|
four bits per byte using the shrn instruction. A count trailing zeros then
|
|
identifies the first zero byte. */
|
|
|
|
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
|
|
cbnz synd, L(loop_end)
|
|
ldr data, [src, 32]!
|
|
cmeq vhas_nul.16b, vdata.16b, 0
|
|
umaxp vend.16b, vhas_nul.16b, vhas_nul.16b
|
|
fmov synd, dend
|
|
cbz synd, L(loop)
|
|
sub src, src, 16
|
|
L(loop_end):
|
|
shrn vend.8b, vhas_nul.8h, 4 /* 128->64 */
|
|
sub result, src, srcin
|
|
fmov synd, dend
|
|
#ifndef __AARCH64EB__
|
|
rbit synd, synd
|
|
#endif
|
|
add result, result, 16
|
|
clz tmp, synd
|
|
add result, result, tmp, lsr 2
|
|
ret
|
|
|
|
END (STRLEN)
|
|
weak_alias (STRLEN, strlen)
|
|
libc_hidden_builtin_def (strlen)
|