1/* strchrnul - find a character or nul in a string
2
3 Copyright (C) 2014-2024 Free Software Foundation, Inc.
4
5 This file is part of the GNU C Library.
6
7 The GNU C Library is free software; you can redistribute it and/or
8 modify it under the terms of the GNU Lesser General Public
9 License as published by the Free Software Foundation; either
10 version 2.1 of the License, or (at your option) any later version.
11
12 The GNU C Library is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 Lesser General Public License for more details.
16
17 You should have received a copy of the GNU Lesser General Public
18 License along with the GNU C Library. If not, see
19 <https://www.gnu.org/licenses/>. */
20
21#include <sysdep.h>
22
23/* Assumptions:
24 *
25 * ARMv8-a, AArch64, Advanced SIMD.
26 * MTE compatible.
27 */
28
29#define srcin x0
30#define chrin w1
31#define result x0
32
33#define src x2
34#define tmp1 x1
35#define tmp2 x3
36
37#define vrepchr v0
38#define vdata v1
39#define qdata q1
40#define vhas_nul v2
41#define vhas_chr v3
42#define vend v4
43#define dend d4
44
45/*
46 Core algorithm:
47 For each 16-byte chunk we calculate a 64-bit nibble mask value with four bits
48 per byte. We take 4 bits of every comparison byte with shift right and narrow
49 by 4 instruction. Since the bits in the nibble mask reflect the order in
50 which things occur in the original string, counting leading zeros identifies
51 exactly which byte matched. */
52
53ENTRY (__strchrnul)
54 PTR_ARG (0)
55 bic src, srcin, 15
56 dup vrepchr.16b, chrin
57 ld1 {vdata.16b}, [src]
58 cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
59 cmhs vhas_chr.16b, vhas_chr.16b, vdata.16b
60 lsl tmp2, srcin, 2
61 shrn vend.8b, vhas_chr.8h, 4 /* 128->64 */
62 fmov tmp1, dend
63 lsr tmp1, tmp1, tmp2 /* Mask padding bits. */
64 cbz tmp1, L(loop)
65
66 rbit tmp1, tmp1
67 clz tmp1, tmp1
68 add result, srcin, tmp1, lsr 2
69 ret
70
71 .p2align 4
72L(loop):
73 ldr qdata, [src, 16]
74 cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
75 cmhs vhas_chr.16b, vhas_chr.16b, vdata.16b
76 umaxp vend.16b, vhas_chr.16b, vhas_chr.16b
77 fmov tmp1, dend
78 cbnz tmp1, L(end)
79 ldr qdata, [src, 32]!
80 cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
81 cmhs vhas_chr.16b, vhas_chr.16b, vdata.16b
82 umaxp vend.16b, vhas_chr.16b, vhas_chr.16b
83 fmov tmp1, dend
84 cbz tmp1, L(loop)
85 sub src, src, 16
86L(end):
87 shrn vend.8b, vhas_chr.8h, 4 /* 128->64 */
88 add src, src, 16
89 fmov tmp1, dend
90#ifndef __AARCH64EB__
91 rbit tmp1, tmp1
92#endif
93 clz tmp1, tmp1
94 add result, src, tmp1, lsr 2
95 ret
96
97END(__strchrnul)
98libc_hidden_def (__strchrnul)
99weak_alias (__strchrnul, strchrnul)
100

source code of glibc/sysdeps/aarch64/strchrnul.S