/*
* 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 C P Y *
// ***************
//
// char* strcpy(const char *dst, const char *src)// 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,
// and never store a byte we don't have to.
//
// 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.
//
// We align the _source_, which allows us to avoid all worries about
// spurious page faults. Doing so is faster than aligning the dest.
//
// In 64-bit mode, the algorithm is doubleword parallel.
.text
.globl EXT(strcpy)
.align 5
LEXT(strcpy) // char* strcpy(const char *dst, const char *src)#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 (must return r3 intact)
beq LwordloopEnter // source is aligned
subfic r0,r0,GPR_BYTES // r0 <- #bytes to align source
mtctr r0
// Loop over bytes.
// r4 = source ptr (unaligned)
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r9 = dest ptr (unaligned)
// ctr = byte count
Lbyteloop:
lbz r8,0(r4) // r8 <- next source byte
addi r4,r4,1
cmpwi r8,0 // 0 ?
stb r8,0(r9) // pack into dest
addi r9,r9,1
bdnzf eq,Lbyteloop // loop until (ctr==0) | (r8==0)
bne LwordloopEnter // 0-byte not found, so enter word loop
blr // 0-byte found, done
// Word loop: move a word or doubleword at a time until 0-byte found.
// r4 = source ptr (aligned)
// r6 = 0xFEFEFEFF
// r7 = 0x80808080
// r9 = dest ptr (unaligned)
.align 5 // align inner loop, which is 8 words ling
Lwordloop:
stg r8,0(r9) // pack word or doubleword into destination
addi r9,r9,GPR_BYTES
LwordloopEnter:
lg r8,0(r4) // r8 <- next source word or doubleword
addi r4,r4,GPR_BYTES
add r10,r8,r6 // r10 <- word + 0xFEFEFEFF
andc r12,r7,r8 // r12 <- ~word & 0x80808080
and. r0,r10,r12 // r0 <- nonzero iff word has a 0-byte
beq Lwordloop // loop if no 0-byte
// 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 // shift leftmost byte into bottom so we can "stb"
slgi r8,r8,8 // move on to next
stb r0,0(r9) // pack into dest
addi r9,r9,1
bne Lstorelastbytes // loop until 0 stored
blr