1 /* rawmemchr -- find a byte within an unsized memory block.
2 Copyright (C) 2013-2016 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 <http://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.
29 ldrb r2, [\B] @ load first byte asap
31 @ To cater to long strings, we want to search through a few
32 @ characters until we reach an aligned pointer. To cater to
33 @ small strings, we don't want to start doing word operations
34 @ immediately. The compromise is a maximum of 16 bytes less
35 @ whatever is required to end with an aligned pointer.
36 @ r3 = number of characters to search in alignment loop
39 rsb r3, r3, #15 @ 16 - 1 peeled loop iteration
44 @ Loop until we find ...
47 subs r3, r3, #1 @ ... the alignment point
49 cmpne r2, r1 @ ... or C
52 @ Disambiguate the exit possibilites above
58 @ So now we're aligned.
61 orr r1, r1, r1, lsl #8 @ Replicate C to all bytes
70 orr r1, r1, r1, lsl #16
72 @ Loop searching for C, 8 bytes at a time.
73 @ Subtracting (unsigned saturating) from 1 means result of 1 for
74 @ any byte that was originally zero and 0 otherwise. Therefore
75 @ we consider the lsb of each byte the "found" bit.
76 2: eor r2, r2, r1 @ Convert C bytes to 0
78 uqsub8 r2, ip, r2 @ Find C
81 orrs r3, r3, r2 @ Test both words for found
84 ldrdeq r2, r3, [\B], #8
87 @ Found something. Disambiguate between first and second words.
88 @ Adjust r0 to point to the word containing the match.
89 @ Adjust r2 to the found bits for the word containing the match.
96 @ Find the bit-offset of the match within the word. Note that the
97 @ bit result from clz will be 7 higher than "true", but we'll
98 @ immediately discard those bits converting to a byte offset.
100 rev r2, r2 @ For LE, count from the little end
103 add r0, r0, r2, lsr #3 @ Adjust the pointer to the found byte
108 weak_alias (__rawmemchr, rawmemchr)
109 libc_hidden_def (__rawmemchr)