/* | |
* Copyright (c) 2011 - 2013, ARM Ltd | |
* All rights reserved. | |
* | |
* Redistribution and use in source and binary forms, with or without | |
* modification, are permitted provided that the following conditions | |
* are met: | |
* 1. Redistributions of source code must retain the above copyright | |
* notice, this list of conditions and the following disclaimer. | |
* 2. Redistributions in binary form must reproduce the above copyright | |
* notice, this list of conditions and the following disclaimer in the | |
* documentation and/or other materials provided with the distribution. | |
* 3. The name of the company may not be used to endorse or promote | |
* products derived from this software without specific prior written | |
* permission. | |
* | |
* THIS SOFTWARE IS PROVIDED BY ARM LTD ``AS IS'' AND ANY EXPRESS OR IMPLIED | |
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF | |
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. | |
* IN NO EVENT SHALL ARM LTD BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, | |
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED | |
* TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR | |
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF | |
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING | |
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS | |
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
*/ | |
.text | |
.align 2 | |
GCC_ASM_EXPORT(memcpy) | |
// Taken from Newlib BSD implementation. | |
ASM_PFX(memcpy): | |
// Copy dst to x6, so we can preserve return value. | |
mov x6, x0 | |
// NOTE: although size_t is unsigned, this code uses signed | |
// comparisons on x2 so relies on nb never having its top bit | |
// set. In practice this is not going to be a real problem. | |
// Require at least 64 bytes to be worth aligning. | |
cmp x2, #64 | |
blt qwordcopy | |
// Compute offset to align destination to 16 bytes. | |
neg x3, x0 | |
and x3, x3, 15 | |
cbz x3, blockcopy // offset == 0 is likely | |
// We know there is at least 64 bytes to be done, so we | |
// do a 16 byte misaligned copy at first and then later do | |
// all 16-byte aligned copies. Some bytes will be copied | |
// twice, but there's no harm in that since memcpy does not | |
// guarantee correctness on overlap. | |
sub x2, x2, x3 // nb -= offset | |
ldp x4, x5, [x1] | |
add x1, x1, x3 | |
stp x4, x5, [x6] | |
add x6, x6, x3 | |
// The destination pointer is now qword (16 byte) aligned. | |
// (The src pointer might be.) | |
blockcopy: | |
// Copy 64 bytes at a time. | |
subs x2, x2, #64 | |
blt 3f | |
2: subs x2, x2, #64 | |
ldp x4, x5, [x1,#0] | |
ldp x8, x9, [x1,#16] | |
ldp x10,x11,[x1,#32] | |
ldp x12,x13,[x1,#48] | |
add x1, x1, #64 | |
stp x4, x5, [x6,#0] | |
stp x8, x9, [x6,#16] | |
stp x10,x11,[x6,#32] | |
stp x12,x13,[x6,#48] | |
add x6, x6, #64 | |
bge 2b | |
// Unwind pre-decrement | |
3: add x2, x2, #64 | |
qwordcopy: | |
// Copy 0-48 bytes, 16 bytes at a time. | |
subs x2, x2, #16 | |
blt tailcopy | |
2: ldp x4, x5, [x1],#16 | |
subs x2, x2, #16 | |
stp x4, x5, [x6],#16 | |
bge 2b | |
// No need to unwind the pre-decrement, it would not change | |
// the low 4 bits of the count. But how likely is it for the | |
// byte count to be multiple of 16? Is it worth the overhead | |
// of testing for x2 == -16? | |
tailcopy: | |
// Copy trailing 0-15 bytes. | |
tbz x2, #3, 1f | |
ldr x4, [x1],#8 // copy 8 bytes | |
str x4, [x6],#8 | |
1: | |
tbz x2, #2, 1f | |
ldr w4, [x1],#4 // copy 4 bytes | |
str w4, [x6],#4 | |
1: | |
tbz x2, #1, 1f | |
ldrh w4, [x1],#2 // copy 2 bytes | |
strh w4, [x6],#2 | |
1: | |
tbz x2, #0, return | |
ldrb w4, [x1] // copy 1 byte | |
strb w4, [x6] | |
return: | |
// This is the only return point of memcpy. | |
ret |