projects / apple / libc.git / blame
| Commit | Line | Data |
|---|---|---|
| b5d655f7 A |
1 | /* |
| 2 | * Copyright (c) 2006 Apple Computer, Inc. All rights reserved. | |
| 3 | * | |
| 4 | * @APPLE_LICENSE_HEADER_START@ | |
| 5 | * | |
| 6 | * This file contains Original Code and/or Modifications of Original Code | |
| 7 | * as defined in and that are subject to the Apple Public Source License | |
| 8 | * Version 2.0 (the 'License'). You may not use this file except in | |
| 9 | * compliance with the License. Please obtain a copy of the License at | |
| 10 | * http://www.opensource.apple.com/apsl/ and read it before using this | |
| 11 | * file. | |
| 12 | * | |
| 13 | * The Original Code and all software distributed under the License are | |
| 14 | * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER | |
| 15 | * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, | |
| 16 | * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, | |
| 17 | * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. | |
| 18 | * Please see the License for the specific language governing rights and | |
| 19 | * limitations under the License. | |
| 20 | * | |
| 21 | * @APPLE_LICENSE_HEADER_END@ | |
| 22 | */ | |
| 23 | ||
| 24 | .text | |
| 25 | .align 2 | |
| 26 | ||
| 27 | .globl _strlen | |
| 28 | /* size_t strlen(const char *s); */ | |
| 29 | _strlen: | |
| 30 | /* save the original pointer */ | |
| 31 | mov r12, r0 | |
| 32 | ||
| 33 | /* see if the string is aligned */ | |
| 34 | ands r3, r0, #3 | |
| 35 | ||
| 36 | /* load the first word, address rounded down */ | |
| 37 | bic r0, r0, #3 | |
| 38 | ldr r2, [r0], #4 | |
| 39 | ||
| 40 | /* skip the next part if the string is already aligned */ | |
| 41 | beq Laligned | |
| 42 | ||
| 43 | Lunaligned: | |
| 44 | /* unaligned pointer, mask out the bytes that we've read that we should be ignoring */ | |
| 45 | cmp r3, #2 | |
| 46 | orr r2, r2, #0x000000ff | |
| 47 | orrge r2, r2, #0x0000ff00 | |
| 48 | orrgt r2, r2, #0x00ff0000 | |
| 49 | ||
| 50 | Laligned: | |
| 51 | /* load 0x01010101 into r1 */ | |
| 52 | mov r1, #0x01 | |
| 53 | orr r1, r1, r1, lsl #8 | |
| 54 | orr r1, r1, r1, lsl #16 | |
| 55 | ||
| 56 | Laligned_loop: | |
| 57 | /* ((x - 0x01010101) & ~x & 0x80808080) == hasnull(word) */ | |
| 58 | sub r3, r2, r1 /* x - 0x01010101 */ | |
| 59 | bic r3, r3, r2 /* above & ~x */ | |
| 60 | tst r3, r1, lsl #7 /* above & 0x80808080 */ | |
| 61 | ldreq r2, [r0], #4 /* load next word */ | |
| 62 | beq Laligned_loop | |
| 63 | ||
| 64 | /* we found a nullbyte */ | |
| 65 | /* r0 (ptr) has overshot by up to 4 bytes, so subtract off until we find a nullbyte */ | |
| 66 | sub r0, r0, #1 | |
| 67 | tst r2, #0x000000ff | |
| 68 | subeq r0, r0, #1 | |
| 69 | tstne r2, #0x0000ff00 | |
| 70 | subeq r0, r0, #1 | |
| 71 | tstne r2, #0x00ff0000 | |
| 72 | subeq r0, r0, #1 | |
| 73 | ||
| 74 | Lexit: | |
| 75 | /* len = ptr - original pointer */ | |
| 76 | sub r0, r0, r12 | |
| 77 | bx lr | |
| 78 |