1/* rawmemchr -- find a byte within an unsized memory block.
2 Copyright (C) 2013-2024 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library. If not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <sysdep.h>
20
21 .syntax unified
22 .text
23
24ENTRY (__rawmemchr)
25 @ r0 = start of string
26 @ r1 = character to match
27 @ returns a pointer to the match, which must be present.
28 ldrb r2, [r0] @ load first byte asap
29
30 @ To cater to long strings, we want to search through a few
31 @ characters until we reach an aligned pointer. To cater to
32 @ small strings, we don't want to start doing word operations
33 @ immediately. The compromise is a maximum of 16 bytes less
34 @ whatever is required to end with an aligned pointer.
35 @ r3 = number of characters to search in alignment loop
36 and r3, r0, #7
37 uxtb r1, r1
38 rsb r3, r3, #15 @ 16 - 1 peeled loop iteration
39 cmp r2, r1
40 it eq
41 bxeq lr
42
43 @ Loop until we find ...
441: ldrb r2, [r0, #1]!
45 subs r3, r3, #1 @ ... the alignment point
46 it ne
47 cmpne r2, r1 @ ... or C
48 bne 1b
49
50 @ Disambiguate the exit possibilities above
51 cmp r2, r1 @ Found C
52 it eq
53 bxeq lr
54 add r0, r0, #1
55
56 @ So now we're aligned.
57 ldrd r2, r3, [r0], #8
58 orr r1, r1, r1, lsl #8 @ Replicate C to all bytes
59#ifdef ARCH_HAS_T2
60 movw ip, #0x0101
61 pld [r0, #64]
62 movt ip, #0x0101
63#else
64 ldr ip, =0x01010101
65 pld [r0, #64]
66#endif
67 orr r1, r1, r1, lsl #16
68
69 @ Loop searching for C, 8 bytes at a time.
70 @ Subtracting (unsigned saturating) from 1 means result of 1 for
71 @ any byte that was originally zero and 0 otherwise. Therefore
72 @ we consider the lsb of each byte the "found" bit.
732: eor r2, r2, r1 @ Convert C bytes to 0
74 eor r3, r3, r1
75 uqsub8 r2, ip, r2 @ Find C
76 uqsub8 r3, ip, r3
77 pld [r0, #128]
78 orrs r3, r3, r2 @ Test both words for found
79 it eq
80 ldrdeq r2, r3, [r0], #8
81 beq 2b
82
83 @ Found something. Disambiguate between first and second words.
84 @ Adjust r0 to point to the word containing the match.
85 @ Adjust r2 to the found bits for the word containing the match.
86 cmp r2, #0
87 sub r0, r0, #4
88 ite eq
89 moveq r2, r3
90 subne r0, r0, #4
91
92 @ Find the bit-offset of the match within the word. Note that the
93 @ bit result from clz will be 7 higher than "true", but we'll
94 @ immediately discard those bits converting to a byte offset.
95#ifdef __ARMEL__
96 rev r2, r2 @ For LE, count from the little end
97#endif
98 clz r2, r2
99 add r0, r0, r2, lsr #3 @ Adjust the pointer to the found byte
100 bx lr
101
102END (__rawmemchr)
103
104weak_alias (__rawmemchr, rawmemchr)
105libc_hidden_def (__rawmemchr)
106

source code of glibc/sysdeps/arm/armv6/rawmemchr.S