/*
* Copyright (c) 2002 Apple Computer, 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@
*/
#define ASSEMBLER
#include <mach/ppc/asm.h>
#undef ASSEMBLER
#define __APPLE_API_PRIVATE
#include <machine/cpu_capabilities.h>
#undef __APPLE_API_PRIVATE
/* We use mode-independent "g" opcodes such as "srgi". These expand
* into word operations when targeting __ppc__, and into doubleword
* operations when targeting __ppc64__.
*/
#include <architecture/ppc/mode_independent_asm.h>
// *****************
// * S T R L C A T *
// *****************
//
// size_t strlcat(char *dst, const char *src, size_t count)// We optimize the move by doing it word parallel. This introduces
// a complication: if we blindly did word load/stores until finding
// a 0, we might get a spurious page fault by touching bytes past it.
// We are allowed to touch the "count" bytes starting at "dst", but
// when appending the "src", we must not do a "lwz" that crosses a page
// boundary, or store past "count".
//
// 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.
//
// Note that "count" is the total buffer length, including the length
// of the "dst" string. This is different than strncat().
//
// In 64-bit mode, this algorithm is doubleword parallel.
.text
.globl EXT(strlcat)
.align 5
LEXT(strlcat) // size_t strlcat(char *dst, const char *src, size_t count)#if defined(__ppc__)
lis r6,hi16(0xFEFEFEFF) // start to generate 32-bit magic constants
lis r7,hi16(0x80808080)
ori r6,r6,lo16(0xFEFEFEFF)
ori r7,r7,lo16(0x80808080)
#else
ld r6,_COMM_PAGE_MAGIC_FE(0) // get 0xFEFEFEFE FEFEFEFF from commpage
ld r7,_COMM_PAGE_MAGIC_80(0) // get 0x80808080 80808080 from commpage
#endif
mr r9,r3 // use r9 for dest ptr (r3 remembers dst start)
beq-- L0bytes // buffer length <4
mtctr r0 // set up loop
b L0words // enter word loop
// Loop over words looking for 0.
// r3 = original start of buffer
// r4 = source ptr (unaligned)
// r5 = original buffer size
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r9 = dest ptr (unaligned)
// ctr = #words or doublewords remaining in buffer
.align 5 // align inner loops for speed
L0words:
lg r8,0(r9) // r8 <- next dest word or doubleword
addi r9,r9,GPR_BYTES
add r10,r8,r6 // r10 <- word + 0xFEFEFEFF
andc r12,r7,r8 // r12 <- ~word & 0x80808080
and. r11,r10,r12 // r11 <- nonzero iff word has a 0-byte
bdnzt eq,L0words // loop until 0 found or buffer end
beq-- L0bytes // skip if 0 not found
slgi r0,r8,7 // move 0x01 bits (false hits) into 0x80 position
subi r9,r9,GPR_BYTES // back up r9 to the start of the word
andc r11,r11,r0 // mask out false hits
cntlzg r0,r11 // find 0 byte (r0 = 0, 8, 16, or 24)
srwi r0,r0,3 // now r0 = 0, 1, 2, or 3
add r9,r9,r0 // now r9 points to the 0-byte in dest
b L0found // start to append source
// Loop over bytes looking for 0.
// r3 = original start of buffer
// r4 = source ptr (unaligned)
// r5 = original buffer size
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r9 = dest ptr (unaligned)
L0bytes:
andi. r0,r5,GPR_BYTES-1 // get #bytes remaining in buffer
mtctr r0 // set up byte loop
beq-- L0notfound // skip if 0 not found in buffer (error)
L0byteloop:
lbz r8,0(r9) // r8 <- next dest byte
addi r9,r9,1
cmpwi r8,0 // 0 ?
bdnzf eq,L0byteloop // loop until 0 found or buffer end
bne-- L0notfound // skip if 0 not found (error)
subi r9,r9,1 // back up, so r9 points to the 0
// End of dest found, so we can start appending source. First, align the source,
// in order to avoid spurious page faults.
// r3 = original start of buffer
// r4 = original source ptr (unaligned)
// r5 = original buffer size
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r9 = ptr to 0-byte in dest (unaligned)
L0found:
andi. r0,r4,GPR_BYTES-1 // is source aligned?
add r5,r5,r3 // get ptr to end of buffer
sub r5,r5,r9 // get #bytes remaining in buffer, counting the 0 (r5>0)
beq Laligned // skip if source already word aligned
subfic r0,r0,GPR_BYTES // not aligned, get #bytes to align r4
b Lbyteloop1 // r5!=0, so skip check
// Copy min(r0,r5) bytes, until 0-byte.
// r0 = #bytes we propose to copy (NOTE: must be >0)
// r4 = source ptr (unaligned)
// r5 = length remaining in buffer (may be 0)
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r9 = dest ptr (unaligned)
Lbyteloop:
cmpgi r5,0 // buffer empty? (note: length is unsigned)
beq-- Loverrun // buffer filled before end of source reached
Lbyteloop1: // entry when we know r5!=0
lbz r8,0(r4) // r8 <- next source byte
subic. r0,r0,1 // decrement count of bytes to move
addi r4,r4,1
subi r5,r5,1 // decrement buffer length remaining
stb r8,0(r9) // pack into dest
cmpwi cr1,r8,0 // 0-byte?
addi r9,r9,1
beq cr1,L0stored // byte was 0, so done
bne Lbyteloop // r0!=0, source not yet aligned
// Source is aligned. Loop over words or doublewords until 0-byte found or end
// of buffer.
// r3 = original start of buffer
// r4 = source ptr (aligned)
// r5 = length remaining in buffer
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r9 = dest ptr (unaligned)
Laligned:
srgi. r8,r5,LOG2_GPR_BYTES// get #words or doublewords in buffer
addi r0,r5,1 // if no words...
beq-- Lbyteloop // ...copy to end of buffer
mtctr r8 // set up loop count
rlwinm r5,r5,0,GPR_BYTES-1 // mask buffer length down to leftover bytes
b LwordloopEnter
// Inner loop: move a word or doubleword at a time, until one of two conditions:
// - a zero byte is found
// - end of buffer
// At this point, registers are as follows:
// r3 = original start of buffer
// r4 = source ptr (aligned)
// r5 = bytes leftover in buffer (0..GPR_BYTES-1)
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r9 = dest ptr (unaligned)
// ctr = loop count
.align 5 // align inner loop, which is 8 words long
Lwordloop:
stg r8,0(r9) // pack word into destination
addi r9,r9,GPR_BYTES
LwordloopEnter:
lg r8,0(r4) // r8 <- next 4 or 8 source bytes
addi r4,r4,GPR_BYTES
add r10,r8,r6 // r10 <- word + 0xFEFEFEFF
andc r12,r7,r8 // r12 <- ~word & 0x80808080
and. r11,r10,r12 // r11 <- nonzero iff word has a 0-byte
bdnzt eq,Lwordloop // loop if ctr!=0 and cr0_eq
beq-- Lleftovers // skip if no 0-byte found, copy leftovers
// Found a 0-byte. Store last word up to and including the 0, a byte at a time.
// r3 = original start of buffer
// r8 = last word, known to have a 0-byte
// r9 = dest ptr (one past 0)
Lstorelastbytes:
srgi. r0,r8,GPR_BYTES*8-8 // right justify next byte and test for 0
slgi r8,r8,8 // shift next byte into position
stb r0,0(r9) // pack into dest
addi r9,r9,1
bne Lstorelastbytes // loop until 0 stored
// Append op successful, O stored into buffer. Return total length.
// r3 = original start of buffer
// r9 = dest ptr (one past 0)
L0stored:
sub r3,r9,r3 // get (length+1) of string in buffer
subi r3,r3,1 // return length
blr
// 0-byte not found in aligned source words. There are up to GPR_BYTES-1 leftover
// source bytes, hopefully the 0-byte is among them.
// r4 = source ptr (aligned)
// r5 = leftover bytes in buffer (0..GPR_BYTES-1)
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r8 = last full word or doubleword of source
// r9 = dest ptr (unaligned)
Lleftovers:
stg r8,0(r9) // store last word
addi r9,r9,GPR_BYTES
addi r0,r5,1 // make sure r5 terminates byte loop (not r0)
b Lbyteloop
// Buffer filled during append without finding the end of source. Overwrite the
// last byte in buffer with a 0, and compute how long the concatenated string would
// have been, if the buffer had been large enough.
// r3 = original start of buffer
// r4 = source ptr (1st byte not copied into buffer)
// r9 = dest ptr (one past end of buffer)
Loverrun:
sub. r3,r9,r3 // compute #bytes stored in buffer
li r0,0 // get a 0
beq-- Lskip // buffer was 0-length
stb r0,-1(r9) // jam in delimiting 0
// Buffer full, check to see how much longer source is. We don't optimize this,
// since overruns are an error.
Lskip:
lbz r8,0(r4) // get next source byte
addi r4,r4,1
addi r3,r3,1 // increment length of "ideal" string
cmpwi r8,0 // 0?
bne Lskip
subi r3,r3,1 // don't count 0 in length
blr // return length of string we "wanted" to create
// 0 not found in buffer (append not yet begun.) We don't store a delimiting 0,
// but do compute how long the concatenated string would have been, assuming the length
// of "dst" is the length of the buffer.
// r3 = original start of buffer
// r4 = original source ptr
// r9 = dest ptr (one past end of buffer)
L0notfound:
sub r3,r9,r3 // compute #bytes in buffer
b Lskip // add strlen(source) to r3