mirror of
https://sourceware.org/git/glibc.git
synced 2024-12-28 21:41:08 +00:00
ad098893ba
Optimize strnlen using the shrn instruction and improve the main loop. Small strings are around 10% faster, large strings are 40% faster on modern CPUs. Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
118 lines
2.7 KiB
ArmAsm
118 lines
2.7 KiB
ArmAsm
/* strnlen - calculate the length of a string with limit.
|
|
|
|
Copyright (C) 2013-2023 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.
|
|
*/
|
|
|
|
#define srcin x0
|
|
#define cntin x1
|
|
#define result x0
|
|
|
|
#define src x2
|
|
#define synd x3
|
|
#define shift x4
|
|
#define tmp x4
|
|
#define cntrem x5
|
|
|
|
#define qdata q0
|
|
#define vdata v0
|
|
#define vhas_chr 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 (__strnlen)
|
|
PTR_ARG (0)
|
|
SIZE_ARG (1)
|
|
bic src, srcin, 15
|
|
cbz cntin, L(nomatch)
|
|
ld1 {vdata.16b}, [src]
|
|
cmeq vhas_chr.16b, vdata.16b, 0
|
|
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)
|
|
L(finish):
|
|
rbit synd, synd
|
|
clz synd, synd
|
|
lsr result, synd, 2
|
|
cmp cntin, result
|
|
csel result, cntin, result, ls
|
|
ret
|
|
|
|
L(nomatch):
|
|
mov result, cntin
|
|
ret
|
|
|
|
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 5
|
|
L(loop32):
|
|
ldr qdata, [src, 32]!
|
|
cmeq vhas_chr.16b, vdata.16b, 0
|
|
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]
|
|
subs cntrem, cntrem, 32
|
|
cmeq vhas_chr.16b, vdata.16b, 0
|
|
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 result, src, srcin
|
|
fmov synd, dend
|
|
#ifndef __AARCH64EB__
|
|
rbit synd, synd
|
|
#endif
|
|
clz synd, synd
|
|
add result, result, synd, lsr 2
|
|
cmp cntin, result
|
|
csel result, cntin, result, ls
|
|
ret
|
|
|
|
END (__strnlen)
|
|
libc_hidden_def (__strnlen)
|
|
weak_alias (__strnlen, strnlen)
|
|
libc_hidden_def (strnlen)
|