projects / apple / libc.git / blame
| Commit | Line | Data |
|---|---|---|
| 8e029c65 | 1 | /* |
| 224c7076 | 2 | * Copyright (c) 2005-2007 Apple Inc. All rights reserved. |
| 8e029c65 A |
3 | * |
| 4 | * @APPLE_LICENSE_HEADER_START@ | |
| 5 | * | |
| 6 | * The contents of this file constitute Original Code as defined in and | |
| 7 | * are subject to the Apple Public Source License Version 1.1 (the | |
| 8 | * "License"). You may not use this file except in compliance with the | |
| 9 | * License. Please obtain a copy of the License at | |
| 10 | * http://www.apple.com/publicsource and read it before using this file. | |
| 11 | * | |
| 12 | * This Original Code and all software distributed under the License are | |
| 13 | * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER | |
| 14 | * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, | |
| 15 | * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, | |
| 16 | * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT. Please see the | |
| 17 | * License for the specific language governing rights and limitations | |
| 18 | * under the License. | |
| 19 | * | |
| 20 | * @APPLE_LICENSE_HEADER_END@ | |
| 21 | */ | |
| 22 | ||
| 23 | /* | |
| 24 | * Strlen, for processors with SSE3. | |
| 25 | * | |
| 26 | * Note that all memory references must be aligned, in order to avoid spurious | |
| 27 | * page faults. Thus we have to load the aligned 16-byte chunk containing the | |
| 28 | * first byte of the operand, then mask out false 0s that may occur before the | |
| 29 | * first byte. | |
| 30 | * | |
| 31 | * We favor the fall-through (ie, short operand) path. | |
| 32 | */ | |
| 33 | ||
| 34 | .text | |
| 35 | .globl _strlen | |
| 36 | .align 4, 0x90 | |
| 37 | _strlen: // size_t strlen(char *b); | |
| 38 | pxor %xmm0,%xmm0 // zero %xmm0 | |
| 224c7076 A |
39 | movl %edi,%ecx // copy low half of ptr |
| 40 | movq %rdi,%rdx // make another full copy | |
| 8e029c65 A |
41 | andq $(-16),%rdi // 16-byte align ptr |
| 42 | orl $(-1),%eax | |
| 43 | pcmpeqb (%rdi),%xmm0 // check whole qw for 0s | |
| 44 | andl $15,%ecx // get #bytes in aligned dq before operand | |
| 45 | shl %cl,%eax // create mask for the bytes of aligned dq in operand | |
| 46 | pmovmskb %xmm0,%ecx // collect mask of 0-bytes | |
| 47 | andl %eax,%ecx // mask out any 0s that occur before 1st byte | |
| 48 | jz LEnterLoop // no 0-bytes (ie, 1-bits), so enter by-16 loop | |
| 49 | ||
| 50 | // We've found a 0-byte. | |
| 51 | // %rdi = aligned address of 16-byte block containing the terminating 0-byte | |
| 52 | // %ecx = compare bit vector | |
| 53 | ||
| 54 | LFoundIt: | |
| 55 | bsf %ecx,%eax // find first 1-bit (ie, first 0-byte) | |
| 224c7076 A |
56 | subq %rdx,%rdi // get length to start of 16-byte block while we wait |
| 57 | addq %rdi,%rax // add bytes in 16-byte block | |
| 8e029c65 A |
58 | ret |
| 59 | ||
| 60 | // Loop over aligned 16-byte blocks: | |
| 61 | // %rdi = address of previous block | |
| 62 | ||
| 63 | LEnterLoop: | |
| 64 | pxor %xmm0,%xmm0 // get some 0-bytes | |
| 65 | addq $16,%rdi // advance ptr | |
| 66 | LLoop: | |
| 67 | movdqa (%rdi),%xmm1 // get next chunk | |
| 68 | addq $16,%rdi | |
| 69 | pcmpeqb %xmm0,%xmm1 // check for 0s | |
| 70 | pmovmskb %xmm1,%ecx // collect mask of 0-bytes | |
| 71 | test %ecx,%ecx // any 0-bytes? | |
| 72 | jz LLoop // no 0-bytes, so get next dq | |
| 73 | ||
| 74 | subq $16,%rdi // back up ptr | |
| 75 | jmp LFoundIt |