/*
* 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
/* 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>
#define __APPLE_API_PRIVATE
#include <machine/cpu_capabilities.h>
#undef __APPLE_API_PRIVATE
// *****************
// * S T R N C A T *
// *****************
//
// char* strncat(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.
// To avoid this, we never do a "lwz" that crosses a page boundary,
// or store extra 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.
//
// Note that "count" refers to the max number of bytes to _append_.
// There is no limit to the number of bytes we will scan looking for
// the end of the "dst" string.
//
// In 64-bit mode, this algorithm is doubleword parallel.
.text
.globl EXT(strncat)
.align 5
LEXT(strncat) // char* strncat(char *dst, const char *src, size_t count) li r10,-1 // get 0xFFs
lg r8,0(r9) // get word or doubleword with 1st operand byte
rlwinm r11,r3,3,(GPR_BYTES-1)*8 // get starting bit position of operand
#if defined(__ppc__)
lis r6,hi16(0xFEFEFEFF) // start to generate 32-bit magic constants
lis r7,hi16(0x80808080)
srw r10,r10,r11 // create a mask of 0xFF bytes for operand in r8
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
srd r10,r10,r11 // create a mask of 0xFF bytes for operand in r8
#endif
orc r8,r8,r10 // make sure bytes preceeding operand are nonzero
b Lword0loopEnter
// Loop over words or doublewords looking for 0-byte marking end of dest.
// r4 = source ptr (unaligned)
// r5 = count (unchanged so far)
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r9 = dest ptr (aligned)
.align 5 // align inner loops for speed
Lword0loop:
lgu r8,GPR_BYTES(r9) // r8 <- next dest word or doubleword
Lword0loopEnter:
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
beq Lword0loop // loop until 0 found
// Now we know one of the bytes in r8 is zero, we just have to figure out which one.
// We have mapped 0 bytes to 0x80, and nonzero bytes to 0x00, with one exception:
// 0x01 bytes preceeding the first zero are also mapped to 0x80. So we have to mask
// out the 0x80s caused by 0x01s before searching for the 0x80 byte. Once the 0 is
// found, we can start appending source. We align the source, which allows us to
// avoid worrying about spurious page faults.
// r4 = source ptr (unaligned)
// r5 = count (unchanged so far)
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r8 = word or doubleword with a 0-byte
// r9 = ptr to the word or doubleword in r8 (aligned)
// r11 = mapped word or doubleword
slgi r10,r8,7 // move 0x01 bits (false hits) into 0x80 position
andi. r0,r4,GPR_BYTES-1 // is source aligned?
andc r11,r11,r10 // mask out false hits
cntlzg r10,r11 // find 0 byte (r0 = 0, 8, 16, or 24)
subfic r0,r0,GPR_BYTES // get #bytes to align r4
srwi r10,r10,3 // now r10 = 0, 1, 2, or 3
add r9,r9,r10 // now r9 points to the 0-byte in dest
beq Laligned // skip if source already aligned
// 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: count is unsigned)
beq-- L0notfound // buffer full but 0 not found
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
beqlr cr1 // 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.
// 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, copy rest of buffer
beq-- Lbyteloop // fewer than 4 bytes in buffer
mtctr r8 // set up word 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:
// r4 = source ptr (aligned)
// r5 = bytes leftover in buffer (0..GPR_BYTES-1)
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r9 = dest ptr (unaligned)
// ctr = whole words or doublewords left in buffer
.align 5 // align inner loop, which is 8 words long
Lwordloop:
stg r8,0(r9) // pack word or doubleword into destination
addi r9,r9,GPR_BYTES
LwordloopEnter:
lg r8,0(r4) // r8 <- next GPR_BYTES 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-- LcheckLeftovers // skip if 0-byte not found
// Found a 0-byte. Store last word up to and including the 0, a byte at a time.
// r8 = last word or doubleword, known to have a 0-byte
// r9 = dest ptr
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
blr
// 0-byte not found while appending words to source. There might be up to
// GPR_BYTES-1 "leftover" bytes to append, hopefully the 0-byte is in there.
// r4 = source ptr (past word in r8)
// r5 = bytes leftover in buffer (0..GPR_BYTES-1)
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r8 = last word or doubleword of source, with no 0-byte
// r9 = dest ptr (unaligned)
LcheckLeftovers:
stg r8,0(r9) // store last whole word or doubleword of source
addi r9,r9,GPR_BYTES
addi r0,r5,1 // let r5 (not r0) terminate byte loop
b Lbyteloop // append last few bytes
// 0-byte not found in source. We append a 0 anyway, even though it will
// be past the end of the buffer. That's the way it's defined.
// r9 = dest ptr
L0notfound:
li r0,0
stb r0,0(r9) // add a 0, past end of buffer
blr