1 /* rawmemchr -- find a byte within an unsized memory block.
2 Copyright (C) 2013-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
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.
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.
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/>. */
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
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
38 rsb r3, r3, #15 @ 16 - 1 peeled loop iteration
43 @ Loop until we find ...
45 subs r3, r3, #1 @ ... the alignment point
47 cmpne r2, r1 @ ... or C
50 @ Disambiguate the exit possibilites above
56 @ So now we're aligned.
58 orr r1, r1, r1, lsl #8 @ Replicate C to all bytes
67 orr r1, r1, r1, lsl #16
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.
73 2: eor r2, r2, r1 @ Convert C bytes to 0
75 uqsub8 r2, ip, r2 @ Find C
78 orrs r3, r3, r2 @ Test both words for found
80 ldrdeq r2, r3, [r0], #8
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.
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.
96 rev r2, r2 @ For LE, count from the little end
99 add r0, r0, r2, lsr #3 @ Adjust the pointer to the found byte
104 weak_alias (__rawmemchr, rawmemchr)
105 libc_hidden_def (__rawmemchr)