1 /* strrchr -- find the last occurence of C in a nul-terminated string
2 Copyright (C) 2013-2021 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 NULL for no match, or a pointer to the match
33 @ Loop a few times until we're aligned.
37 cmp r2, r1 @ Find the character
43 tst r3, #7 @ Find the aligment point
46 @ So now we're aligned. Now we actually need a stack frame.
47 2: push { r4, r5, r6, r7 }
48 cfi_adjust_cfa_offset (16)
49 cfi_rel_offset (r4, 0)
50 cfi_rel_offset (r5, 4)
51 cfi_rel_offset (r6, 8)
52 cfi_rel_offset (r7, 12)
54 orr r1, r1, r1, lsl #8 @ Replicate C to all bytes
61 orr r1, r1, r1, lsl #16
62 mov r2, #0 @ No found bits yet
64 @ Loop searching for EOS and C, 8 bytes at a time.
65 @ Any time we find a match in a word, we copy the address of
66 @ the word to r0, and the found bits to r2.
67 3: ldrd r4, r5, [r3], #8
68 @ Subtracting (unsigned saturating) from 1 means result of 1 for
69 @ any byte that was originally zero and 0 otherwise. Therefore
70 @ we consider the lsb of each byte the "found" bit.
71 uqsub8 r6, ip, r4 @ Find EOS
73 eor r4, r4, r1 @ Convert C bytes to 0
75 uqsub8 r4, ip, r4 @ Find C
77 cmp r6, #0 @ Found EOS, first word
79 cmp r4, #0 @ Handle C, first word
83 cmp r7, #0 @ Found EOS, second word
85 cmp r5, #0 @ Handle C, second word
91 @ Found EOS in second word; fold to first word.
92 5: add r3, r3, #4 @ Dec pointer to 2nd word, with below
93 mov r4, r5 @ Overwrite first word C found
94 mov r6, r7 @ Overwrite first word EOS found
96 @ Found EOS. Zap found C after EOS.
97 4: sub r3, r3, #8 @ Decrement pointer to first word
99 @ Byte swap to be congruent with LE, which is easier from here on.
100 rev r6, r6 @ Byte swap found EOS,
101 rev r4, r4 @ ... this found C
102 rev r2, r2 @ ... prev found C
104 sub r7, r6, #1 @ Toggle EOS lsb and below
105 eor r6, r6, r7 @ All bits below and including lsb
106 ands r4, r4, r6 @ Zap C above EOS
108 movne r2, r4 @ Copy to result, if still non-zero
111 pop { r4, r5, r6, r7 }
112 cfi_adjust_cfa_offset (-16)
118 @ Adjust the result pointer if we found a word containing C.
120 clz r2, r2 @ Find the bit offset of the last C
122 rsbne r2, r2, #32 @ Convert to a count from the right
123 addne r0, r0, r2, lsr #3 @ Convert to byte offset and add.
128 weak_alias (strrchr, rindex)
129 libc_hidden_builtin_def (strrchr)