projects / thirdparty / glibc.git / blame
| Commit | Line | Data |
|---|---|---|
| f5ad94e0 | 1 | /* strchr -- find the first instance of C in a nul-terminated string. |
| 688903eb | 2 | Copyright (C) 2013-2018 Free Software Foundation, Inc. |
| f5ad94e0 RH |
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 | <http://www.gnu.org/licenses/>. */ | |
| 18 | ||
| 19 | #include <sysdep.h> | |
| 20 | ||
| 21 | .syntax unified | |
| 22 | .text | |
| 23 | ||
| 24 | ENTRY (strchr) | |
| 25 | @ r0 = start of string | |
| 26 | @ r1 = character to match | |
| 27 | @ returns NULL for no match, or a pointer to the match | |
| 81cb7a0b | 28 | ldrb r2, [r0] @ load the first byte asap |
| f5ad94e0 RH |
29 | uxtb r1, r1 |
| 30 | ||
| 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 | |
| 37 | and r3, r0, #7 | |
| 38 | rsb r3, r3, #15 @ 16 - 1 peeled loop iteration | |
| 39 | cmp r2, r1 @ Found C? | |
| 40 | it ne | |
| 41 | cmpne r2, #0 @ Found EOS? | |
| 42 | beq 99f | |
| 43 | ||
| 44 | @ Loop until we find ... | |
| 81cb7a0b | 45 | 1: ldrb r2, [r0, #1]! |
| f5ad94e0 RH |
46 | subs r3, r3, #1 @ ... the aligment point |
| 47 | it ne | |
| 48 | cmpne r2, r1 @ ... or the character | |
| 49 | it ne | |
| 50 | cmpne r2, #0 @ ... or EOS | |
| 51 | bne 1b | |
| 52 | ||
| 53 | @ Disambiguate the exit possibilites above | |
| 54 | cmp r2, r1 @ Found the character | |
| 55 | it ne | |
| 56 | cmpne r2, #0 @ Found EOS | |
| 57 | beq 99f | |
| 58 | add r0, r0, #1 | |
| 59 | ||
| 60 | @ So now we're aligned. Now we actually need a stack frame. | |
| 61 | push { r4, r5, r6, r7 } | |
| 62 | cfi_adjust_cfa_offset (16) | |
| 63 | cfi_rel_offset (r4, 0) | |
| 64 | cfi_rel_offset (r5, 4) | |
| 65 | cfi_rel_offset (r6, 8) | |
| 66 | cfi_rel_offset (r7, 12) | |
| 67 | ||
| 81cb7a0b | 68 | ldrd r2, r3, [r0], #8 |
| f5ad94e0 RH |
69 | orr r1, r1, r1, lsl #8 @ Replicate C to all bytes |
| 70 | #ifdef ARCH_HAS_T2 | |
| 71 | movw ip, #0x0101 | |
| 81cb7a0b | 72 | pld [r0, #64] |
| f5ad94e0 RH |
73 | movt ip, #0x0101 |
| 74 | #else | |
| 75 | ldr ip, =0x01010101 | |
| 81cb7a0b | 76 | pld [r0, #64] |
| f5ad94e0 RH |
77 | #endif |
| 78 | orr r1, r1, r1, lsl #16 | |
| 79 | ||
| 80 | @ Loop searching for EOS or C, 8 bytes at a time. | |
| 81 | 2: | |
| 82 | @ Subtracting (unsigned saturating) from 1 means result of 1 for | |
| 83 | @ any byte that was originally zero and 0 otherwise. Therefore | |
| 84 | @ we consider the lsb of each byte the "found" bit. | |
| 85 | uqsub8 r4, ip, r2 @ Find EOS | |
| 86 | eor r6, r2, r1 @ Convert C bytes to 0 | |
| 87 | uqsub8 r5, ip, r3 | |
| 88 | eor r7, r3, r1 | |
| 89 | uqsub8 r6, ip, r6 @ Find C | |
| 81cb7a0b | 90 | pld [r0, #128] @ Prefetch 2 lines ahead |
| f5ad94e0 RH |
91 | uqsub8 r7, ip, r7 |
| 92 | orr r4, r4, r6 @ Combine found for EOS and C | |
| 93 | orr r5, r5, r7 | |
| 94 | orrs r6, r4, r5 @ Combine the two words | |
| 95 | it eq | |
| 81cb7a0b | 96 | ldrdeq r2, r3, [r0], #8 |
| f5ad94e0 RH |
97 | beq 2b |
| 98 | ||
| 99 | @ Found something. Disambiguate between first and second words. | |
| 100 | @ Adjust r0 to point to the word containing the match. | |
| 101 | @ Adjust r2 to the contents of the word containing the match. | |
| 102 | @ Adjust r4 to the found bits for the word containing the match. | |
| 103 | cmp r4, #0 | |
| 104 | sub r0, r0, #4 | |
| 105 | itte eq | |
| 106 | moveq r4, r5 | |
| 107 | moveq r2, r3 | |
| 108 | subne r0, r0, #4 | |
| 109 | ||
| 110 | @ Find the bit-offset of the match within the word. | |
| 111 | #if defined(__ARMEL__) | |
| 112 | @ For LE, swap the found word so clz searches from the little end. | |
| 113 | rev r4, r4 | |
| 114 | #else | |
| 115 | @ For BE, byte swap the word to make it easier to extract the byte. | |
| 116 | rev r2, r2 | |
| 117 | #endif | |
| 118 | @ We're counting 0x01 (not 0x80), so the bit offset is 7 too high. | |
| 119 | clz r3, r4 | |
| 120 | sub r3, r3, #7 | |
| 121 | lsr r2, r2, r3 @ Shift down found byte | |
| 122 | uxtb r1, r1 @ Undo replication of C | |
| 123 | uxtb r2, r2 @ Extract found byte | |
| 124 | add r0, r0, r3, lsr #3 @ Adjust the pointer to the found byte | |
| 125 | ||
| 126 | pop { r4, r5, r6, r7 } | |
| 127 | cfi_adjust_cfa_offset (-16) | |
| 128 | cfi_restore (r4) | |
| 129 | cfi_restore (r5) | |
| 130 | cfi_restore (r6) | |
| 131 | cfi_restore (r7) | |
| 132 | ||
| 133 | @ Disambiguate between EOS and C. | |
| 134 | 99: | |
| 135 | cmp r2, r1 | |
| 136 | it ne | |
| 137 | movne r0, #0 @ Found EOS, return NULL | |
| 138 | bx lr | |
| 139 | ||
| 140 | END (strchr) | |
| 141 | ||
| 142 | weak_alias (strchr, index) | |
| 143 | libc_hidden_builtin_def (strchr) |