/*
* 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 A T *
// *****************
//
// size_t strlcat(char *dst, const char *src, size_t size)// We use SSE to do the initial strlen(), and word-parallel copies
// to do the move. This appears to be faster than either all SSE
// or all word-parallel, at least on Core2 class machines.
//
// Using 4- or 16-byte parallel loops introduce a complication:
// if we blindly did parallel 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 word parallel test for 0s relies on the following inobvious
// but very efficient 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.
//
// On Core2 class machines, this algorithm seems to be faster than the
// naive byte-by-byte version for operands longer than about 10 bytes.
.text
.globl _strlcat
.align 4
_strlcat: // size_t *strlcat(char *dst, const char *src, size_t size) pushl %esi
pushl %ebx
movl 16(%esp),%edi // get dest ptr
movl 20(%esp),%esi // get source ptr
movl 24(%esp),%ebx // get length of buffer
// Use SSE to find the 0-byte at current end of buffer.
// This is just a minor variant of strlen().
movl %edi,%ecx // copy buffer ptr
andl $(-16),%edi // 16-byte align buffer ptr
pxor %xmm0,%xmm0 // get some 0s
andl $15,%ecx // get #bytes in dq before start of buffer
movl $16,%edx
orl $(-1),%eax
subl %ecx,%edx // #bytes from buffer start to end of dq
subl %edx,%ebx // does buffer end before end of dq?
jb LShortBuf1 // yes, drop into byte-by-byte mode
movdqa (%edi),%xmm1 // get first aligned chunk of buffer
addl $16,%edi
pcmpeqb %xmm0,%xmm1 // check for 0s
shl %cl,%eax // create mask for the bytes of aligned dq in operand
pmovmskb %xmm1,%ecx // collect mask of 0-bytes
andl %eax,%ecx // mask out any 0s that occur before buffer start
jnz 2f // found end of buffer
1:
subl $16,%ebx // another dq in buffer?
jb LShortBuf2 // no, drop into byte-by-byte mode
movdqa (%edi),%xmm1 // get next chunk
addl $16,%edi
pcmpeqb %xmm0,%xmm1 // check for 0s
pmovmskb %xmm1,%ecx // collect mask of 0-bytes
testl %ecx,%ecx // any 0-bytes?
jz 1b // no
2:
bsf %ecx,%edx // find first 1-bit (ie, first 0-byte)
subl $16,%edi // back up ptr into buffer
addl $16,%ebx // recover length remaining as of start of dq
addl %edx,%edi // point to 0-byte
subl %edx,%ebx // compute #bytes remaining in buffer
// Copy byte-by-byte until source is 4-byte aligned.
// %edi = points to 1st byte available in buffer
// %esi = src ptr
// %ebx = buffer length remaining (ie, starting at %edi)
//
// NB: the rest of this code is cut-and-pasted from strlcpy().
movl %esi,%edx // copy source ptr
negl %edx
andl $3,%edx // how many bytes to align source ptr?
jz LAligned // already aligned
// Loop over bytes.
// %edi = dest ptr
// %esi = source ptr
// %ebx = length remaining in buffer
// %edx = number of bytes to copy (>0, may not fit in buffer)
LLoopOverBytes:
movzb (%esi),%eax // get source byte before checking buffer length
testl %ebx,%ebx // buffer full?
jz L0NotFound // yes
inc %esi
dec %ebx
movb %al,(%edi) // pack into dest
inc %edi
testl %eax,%eax // 0?
jz LDone // yes, done
dec %edx // more to go?
jnz LLoopOverBytes
// Source is aligned. Loop over words until end of buffer. We
// align the source, rather than the dest, to avoid getting spurious page faults.
// %edi = dest ptr (unaligned)
// %esi = source ptr (word aligned)
// %ebx = length remaining in buffer
LAligned:
movl $5,%edx // if buffer almost exhausted, prepare to copy rest byte-by-byte
cmpl $4,%ebx // enough for at least one word?
jb LLoopOverBytes
// Loop over words.
// %edi = dest ptr (unaligned)
// %esi = source ptr (word aligned)
// %ebx = length remaining in buffer (>=4)
LLoopOverWords:
movl (%esi),%eax // get next 4 bytes of source
subl $4,%ebx
addl $4,%esi
movl %eax,%edx // make 2 copies of word
movl %eax,%ecx
notl %edx // use magic word-parallel test for 0s
addl $0xFEFEFEFF,%ecx
andl $0x80808080,%edx
testl %ecx,%edx
jnz L0Found // one of the bytes of %eax is a 0
movl %eax,(%edi) // pack 4 bytes into destination
addl $4,%edi
cmpl $4,%ebx // room in buffer for another word?
jae LLoopOverWords // yes
movl %ebx,%edx // copy leftovers in byte loop
jmp LLoopOverBytes
// Found a 0-byte in the word of source. Store a byte at a time until the 0.
// %edi = dest ptr (unaligned)
// %eax = last word of source, known to have a 0-byte
LNextByte:
shrl $8,%eax // next byte
L0Found:
movb %al,(%edi) // pack in next byte
incl %edi
testb %al,%al // 0?
jnz LNextByte
// Done storing string.
// %edi = ptr to byte after 0-byte
LDone:
subl 16(%esp),%edi // subtract original dest ptr to get length stored
decl %edi // don't count the 0-byte
movl %edi,%eax // copy to return value
LExit:
popl %ebx
popl %esi
popl %edi
ret
// Buffer filled but 0-byte not found. We return the length of the buffer plus the length
// of the source string. This is not optimized, as it is an error condition.
// %edi = dest ptr (ie, 1 past end of buffer)
// %esi = source ptr (ptr to 1st byte that does not fit)
L0NotFound:
movl 24(%esp),%eax // reload buffer length
testl %eax,%eax // null?
jz LScanSourceTo0 // yes, cannot store a 0
xorl %edx,%edx // get a 0
movb %dl,-1(%edi) // store a 0 at end of buffer to delimit string
LScanSourceTo0:
movzb (%esi),%edx // get next byte of source
incl %esi
incl %eax
testl %edx,%edx // 0?
jnz LScanSourceTo0
decl %eax // don't count the 0-byte
jmp LExit
// Buffer too short to reach end of even one 16-byte aligned chunk.
// %esi = src ptr
LShortBuf1:
movl 16(%esp),%edi // recover ptr to start of buffer
movl 24(%esp),%ebx // recover buffer length
jmp LShortBuf3
// Out of aligned dq's of buffer, 0-byte still not found.
// %esi = src ptr
// %edi = 1st buffer byte not checked for 0
// %ebx = length remaining - 16
LShortBuf2:
addl $16,%ebx // length remaining
LShortBuf3:
movl 24(%esp),%eax // recover original buffer length, in case 0-byte not found
movl $17,%edx // buffer almost exhausted, prepare to copy byte-by-byte
1:
testl %ebx,%ebx // no 0s in buffer at all?
jz LScanSourceTo0 // yes, cannot store a 0
cmpb $0,(%edi) // is this the 0?
jz LLoopOverBytes // yes, append source
incl %edi
decl %ebx
jmp 1b // loop looking for 0