/*
* Copyright (c) 2005-2007 Apple Inc. All rights reserved.
*
* @APPLE_LICENSE_HEADER_START@
*
* The contents of this file constitute Original Code as defined in and
* are subject to the Apple Public Source License Version 1.1 (the
* "License"). You may not use this file except in compliance with the
* License. Please obtain a copy of the License at
* http://www.apple.com/publicsource and read it before using this file.
*
* This Original Code and all software distributed under the License are
* distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
* EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
* INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT. Please see the
* License for the specific language governing rights and limitations
* under the License.
*
* @APPLE_LICENSE_HEADER_END@
*/
/*
* Strlen, for processors with SSE3.
*
* Note that all memory references must be aligned, in order to avoid spurious
* page faults. Thus we have to load the aligned 16-byte chunk containing the
* first byte of the operand, then mask out false 0s that may occur before the
* first byte.
*
* We favor the fall-through (ie, short operand) path.
*/
.text
.globl _strlen
.align 4, 0x90
_strlen: // size_t strlen(char *b) movl %edi,%ecx // copy low half of ptr
movq %rdi,%rdx // make another full copy
andq $(-16),%rdi // 16-byte align ptr
orl $(-1),%eax
pcmpeqb (%rdi),%xmm0 // check whole qw for 0s
andl $15,%ecx // get #bytes in aligned dq before operand
shl %cl,%eax // create mask for the bytes of aligned dq in operand
pmovmskb %xmm0,%ecx // collect mask of 0-bytes
andl %eax,%ecx // mask out any 0s that occur before 1st byte
jz LEnterLoop // no 0-bytes (ie, 1-bits), so enter by-16 loop
// We've found a 0-byte.
// %rdi = aligned address of 16-byte block containing the terminating 0-byte
// %ecx = compare bit vector
LFoundIt:
bsf %ecx,%eax // find first 1-bit (ie, first 0-byte)
subq %rdx,%rdi // get length to start of 16-byte block while we wait
addq %rdi,%rax // add bytes in 16-byte block
ret
// Loop over aligned 16-byte blocks:
// %rdi = address of previous block
LEnterLoop:
pxor %xmm0,%xmm0 // get some 0-bytes
addq $16,%rdi // advance ptr
LLoop:
movdqa (%rdi),%xmm1 // get next chunk
addq $16,%rdi
pcmpeqb %xmm0,%xmm1 // check for 0s
pmovmskb %xmm1,%ecx // collect mask of 0-bytes
test %ecx,%ecx // any 0-bytes?
jz LLoop // no 0-bytes, so get next dq
subq $16,%rdi // back up ptr
jmp LFoundIt