1 | /* strrchr -- find the last occurrence of C in a nul-terminated string |
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 | |
24 | ENTRY (strrchr) |
25 | @ r0 = start of string |
26 | @ r1 = character to match |
27 | @ returns NULL for no match, or a pointer to the match |
28 | |
29 | mov r3, r0 |
30 | mov r0, #0 |
31 | uxtb r1, r1 |
32 | |
33 | @ Loop a few times until we're aligned. |
34 | tst r3, #7 |
35 | beq 2f |
36 | 1: ldrb r2, [r3], #1 |
37 | cmp r2, r1 @ Find the character |
38 | it eq |
39 | subeq r0, r3, #1 |
40 | cmp r2, #0 @ Find EOS |
41 | it eq |
42 | bxeq lr |
43 | tst r3, #7 @ Find the alignment point |
44 | bne 1b |
45 | |
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) |
53 | |
54 | orr r1, r1, r1, lsl #8 @ Replicate C to all bytes |
55 | #ifdef ARCH_HAS_T2 |
56 | movw ip, #0x0101 |
57 | movt ip, #0x0101 |
58 | #else |
59 | ldr ip, =0x01010101 |
60 | #endif |
61 | orr r1, r1, r1, lsl #16 |
62 | mov r2, #0 @ No found bits yet |
63 | |
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 |
72 | uqsub8 r7, ip, r5 |
73 | eor r4, r4, r1 @ Convert C bytes to 0 |
74 | eor r5, r5, r1 |
75 | uqsub8 r4, ip, r4 @ Find C |
76 | uqsub8 r5, ip, r5 |
77 | cmp r6, #0 @ Found EOS, first word |
78 | bne 4f |
79 | cmp r4, #0 @ Handle C, first word |
80 | itt ne |
81 | subne r0, r3, #8 |
82 | movne r2, r4 |
83 | cmp r7, #0 @ Found EOS, second word |
84 | bne 5f |
85 | cmp r5, #0 @ Handle C, second word |
86 | itt ne |
87 | subne r0, r3, #4 |
88 | movne r2, r5 |
89 | b 3b |
90 | |
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 |
95 | |
96 | @ Found EOS. Zap found C after EOS. |
97 | 4: sub r3, r3, #8 @ Decrement pointer to first word |
98 | #ifdef __ARMEB__ |
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 |
103 | #endif |
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 |
107 | itt ne |
108 | movne r2, r4 @ Copy to result, if still non-zero |
109 | movne r0, r3 |
110 | |
111 | pop { r4, r5, r6, r7 } |
112 | cfi_adjust_cfa_offset (-16) |
113 | cfi_restore (r4) |
114 | cfi_restore (r5) |
115 | cfi_restore (r6) |
116 | cfi_restore (r7) |
117 | |
118 | @ Adjust the result pointer if we found a word containing C. |
119 | cmp r2, #0 |
120 | clz r2, r2 @ Find the bit offset of the last C |
121 | itt ne |
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. |
124 | bx lr |
125 | |
126 | END (strrchr) |
127 | |
128 | weak_alias (strrchr, rindex) |
129 | libc_hidden_builtin_def (strrchr) |
130 | |