/*
* Copyright (c) 2007 Apple Inc. All rights reserved.
*
* @APPLE_LICENSE_HEADER_START@
*
* This file contains Original Code and/or Modifications of Original Code
* as defined in and that are subject to the Apple Public Source License
* Version 2.0 (the 'License'). You may not use this file except in
* compliance with the License. Please obtain a copy of the License at
* http://www.opensource.apple.com/apsl/ and read it before using this
* file.
*
* The 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, QUIET ENJOYMENT OR NON-INFRINGEMENT.
* Please see the License for the specific language governing rights and
* limitations under the License.
*
* @APPLE_LICENSE_HEADER_END@
*/
// *****************
// * S T R L C P Y *
// *****************
//
// size_t strlcpy(char *dst, const char *src, size_t size)// We optimize the move by doing it quadword parallel. This introduces
// a complication: if we blindly did quadword load/stores until finding
// a 0, we might get a spurious page fault by touching bytes past it.
// To avoid this, we never do a load that crosses a page boundary,
// or store unnecessary bytes.
//
// The test for 0s relies on the following inobvious but very efficient
// word-parallel test:
// x = dataWord + 0xFEFEFEFF
// y = ~dataWord & 0x80808080
// if (x & y) == 0 then no zero found
// The test maps any non-zero byte to zero, and any zero byte to 0x80,
// with one exception: 0x01 bytes preceeding the first zero are also
// mapped to 0x80.
.text
.globl _strlcpy
// When initially entered:
// %rdi = dest buffer ptr
// %rsi = source ptr
// %rdx = length
.align 4
_strlcpy: // size_t *strlcpy(char *dst, const char *src, size_t size) movq %rdi,%r10 // copy dest ptr
negl %ecx
andl $7,%ecx // how many bytes to align source ptr?
jz LAligned // already aligned
// Loop over bytes.
// %rdi = dest ptr
// %rsi = source ptr
// %rdx = length remaining in buffer
// %ecx = number of bytes to copy (>0, may not fit in buffer)
// %r10 = original dest ptr
LLoopOverBytes:
movzb (%rsi),%eax // get source byte before checking buffer length
testq %rdx,%rdx // buffer full?
jz L0NotFound // yes
incq %rsi
decq %rdx
movb %al,(%rdi) // pack into dest
incq %rdi
testl %eax,%eax // 0?
jz LDone // yes, done
decl %ecx // more to go?
jnz LLoopOverBytes
// Source is aligned. Loop over quadwords until end of buffer. We
// align the source, rather than the dest, to avoid getting spurious page faults.
// %rdi = dest ptr (unaligned)
// %rsi = source ptr (quadword aligned)
// %rdx = length remaining in buffer
// %r10 = original dest ptr
LAligned:
movl $9,%ecx // if buffer almost exhausted, prepare to copy rest byte-by-byte
cmpq $8,%rdx // enough for at least one word?
jb LLoopOverBytes
movq $0xFEFEFEFEFEFEFEFF,%rcx // load magic constants
movq $0x8080808080808080,%r11
// Loop over quadwords.
// %rdi = dest ptr (unaligned)
// %rsi = source ptr (word aligned)
// %rdx = length remaining in buffer (>=8)
// %rcx = 0xFEFEFEFEFEFEFEFF
// %r11 = 0x8080808080808080
// %r10 = original dest ptr
LLoopOverQuads:
movq (%rsi),%rax // get next 8 bytes of source
subq $8,%rdx
addq $8,%rsi
movq %rax,%r8 // make 2 copies of quadword
movq %rax,%r9
notq %r8 // use magic word-parallel test for 0s
addq %rcx,%r9
andq %r11,%r8
testq %r8,%r9
jnz L0Found // one of the bytes of %rax is a 0
movq %rax,(%rdi) // pack 8 bytes into destination
addq $8,%rdi
cmpq $8,%rdx // room in buffer for another quadword?
jae LLoopOverQuads // yes
movl %edx,%ecx // copy leftovers in byte loop
jmp LLoopOverBytes
// Found a 0-byte in the quadword of source. Store a byte at a time until the 0.
// %rdi = dest ptr (unaligned)
// %rax = last quadword of source, known to have a 0-byte
// %r10 = original dest ptr
LNextByte:
shrq $8,%rax // next byte
L0Found:
movb %al,(%rdi) // pack in next byte
incq %rdi
testb %al,%al // 0?
jnz LNextByte
// Done storing string.
// %rdi = ptr to byte after 0-byte
// %r10 = original dest ptr
LDone:
subq %r10,%rdi // subtract original dest ptr to get length stored
lea -1(%rdi),%rax // minus one for 0-byte, and move to return value
ret
// Buffer filled but 0-byte not found. We return the length of the source string.
// This is not optimized, as it is an error condition.
// %rdi = dest ptr (ie, 1 past end of buffer)
// %rsi = source ptr (ptr to 1st byte that does not fit)
// %r10 = original dest ptr
L0NotFound:
movq %rdi,%rax // end of buffer...
subq %r10,%rax // ...minus start is buffer length
jz 1f // 0-length buffer, cannot store a 0
xorl %edx,%edx // get a 0
movb %dl,-1(%rdi) // store a 0 at end of buffer to delimit string
1:
movzb (%rsi),%ecx // get next byte of source
incq %rsi
incq %rax
testl %ecx,%ecx // 0?
jnz 1b
decq %rax // don't count the 0-byte
ret