/*
* Copyright (c) 2002 Apple Computer, Inc. All rights reserved.
*
* @APPLE_LICENSE_HEADER_START@
*
* Copyright (c) 1999-2003 Apple Computer, Inc. All Rights Reserved.
*
* 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
// *****************
// * S T R N C P Y *
// *****************
//
// char* strncpy(const char *dst, const char *src, size_t len))// 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 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 EXT(strncpy)
.align 5
LEXT(strncpy)
andi. r0,r4,3 // is source aligned?
dcbt 0,r4 // touch in source
lis r6,hi16(0xFEFEFEFF) // start to load magic constants
lis r7,hi16(0x80808080)
dcbtst 0,r3 // touch in dst
ori r6,r6,lo16(0xFEFEFEFF)
ori r7,r7,lo16(0x80808080)
mr r9,r3 // use r9 for dest ptr (must return r3 intact)
add r2,r3,r5 // remember where end of buffer is
beq Laligned // source is aligned
subfic r0,r0,4 // r0 <- #bytes to word align source
// Copy min(r0,r5) bytes, until 0-byte.
// r0 = #bytes we propose to copy (NOTE: must be >0)
// r2 = ptr to 1st byte not in buffer
// r4 = source ptr (unaligned)
// r5 = length remaining in buffer (may be 0)
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r9 = dest ptr (unaligned)
Lbyteloop:
cmpwi r5,0 // buffer empty? (note: unsigned)
beqlr-- // 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
beq cr1,L0found // byte was 0
bne Lbyteloop // r0!=0, source not yet aligned
// Source is word aligned. Loop over words until end of buffer. Note that we
// have aligned the source, rather than the dest, in order to avoid spurious
// page faults.
// r2 = ptr to 1st byte not in buffer
// r4 = source ptr (word aligned)
// r5 = length remaining in buffer
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r9 = dest ptr (unaligned)
Laligned:
srwi. r8,r5,2 // get #words in buffer
addi r0,r5,1 // if no words, compare rest of buffer
beq-- Lbyteloop // r8==0, no words
mtctr r8 // set up word loop count
rlwinm r5,r5,0,0x3 // mask buffer length down to leftover bytes
b LwordloopEnter
// Move a word at a time, until one of two conditions:
// - a zero byte is found
// - end of buffer
// At this point, registers are as follows:
// r2 = ptr to 1st byte not in buffer
// r4 = source ptr (word aligned)
// r5 = leftover bytes in buffer (0..3)
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r9 = dest ptr (unaligned)
// ctr = whole words left in buffer
.align 5 // align inner loop, which is 8 words long
Lwordloop:
stw r8,0(r9) // pack word into destination
addi r9,r9,4
LwordloopEnter:
lwz r8,0(r4) // r8 <- next 4 source bytes
addi r4,r4,4
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
stw r8,0(r9) // pack in last word
addi r9,r9,4
addi r0,r5,1 // if no 0-byte found...
beq-- Lbyteloop // ...fill rest of buffer a byte at a time
// Found a 0-byte, point to following byte with r9.
slwi r0,r8,7 // move 0x01 false hit bits to 0x80 position
andc r11,r11,r0 // mask out false hits
cntlzw r0,r11 // find the 0-byte (r0 = 0,8,16, or 24)
srwi r0,r0,3 // now r0 = 0, 1, 2, or 3
subfic r0,r0,3 // now r0 = 3, 2, 1, or 0
sub r9,r9,r0 // now r9 points one past the 0-byte
// Zero rest of buffer, if any. We don't simply branch to bzero or memset, because
// r3 is set up incorrectly, and there is a fair amt of overhead involved in using them.
// Instead we use a simpler routine, which will nonetheless be faster unless the number
// of bytes to 0 is large and we're on a 64-bit machine.
// r2 = ptr to 1st byte not in buffer
// r9 = ptr to 1st byte to zero
L0found:
sub r5,r2,r9 // r5 <- #bytes to zero (ie, rest of buffer)
cmplwi r5,32 // how many?
neg r8,r9 // start to compute #bytes to align ptr
li r0,0 // get a 0
blt Ltail // skip if <32 bytes
andi. r10,r8,31 // get #bytes to 32-byte align
sub r5,r5,r10 // adjust buffer length
srwi r11,r5,5 // get #32-byte chunks
cmpwi cr1,r11,0 // any chunks?
mtctr r11 // set up dcbz loop count
beq 1f // skip if already 32-byte aligned
// 32-byte align. We just store 32 0s, rather than test and use conditional
// branches.
stw r0,0(r9) // zero next 32 bytes
stw r0,4(r9)
stw r0,8(r9)
stw r0,12(r9)
stw r0,16(r9)
stw r0,20(r9)
stw r0,24(r9)
stw r0,28(r9)
add r9,r9,r10 // now r9 is 32-byte aligned
beq cr1,Ltail // skip if no 32-byte chunks
b 1f
// Loop doing 32-byte version of DCBZ instruction.
.align 4 // align the inner loop
1:
dcbz 0,r9 // zero another 32 bytes
addi r9,r9,32
bdnz 1b
// Store trailing bytes.
// r0 = 0
// r5 = #bytes to store (<32)
// r9 = address
Ltail:
mtcrf 0x02,r5 // remaining byte count to cr6 and cr7
mtcrf 0x01,r5
bf 27,2f // 16-byte chunk?
stw r0,0(r9)
stw r0,4(r9)
stw r0,8(r9)
stw r0,12(r9)
addi r9,r9,16
2:
bf 28,4f // 8-byte chunk?
stw r0,0(r9)
stw r0,4(r9)
addi r9,r9,8
4:
bf 29,5f // word?
stw r0,0(r9)
addi r9,r9,4
5:
bf 30,6f // halfword?
sth r0,0(r9)
addi r9,r9,2
6:
bflr 31 // byte?
stb r0,0(r9)
blr