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/*
* memcpy - copy memory area
*
* Copyright (c) 2012-2019, Arm Limited.
* SPDX-License-Identifier: MIT
*/
/* Assumptions:
*
* ARMv8-a, AArch64, unaligned accesses.
*
*/
#include "../asmdefs.h"
#define dstin x0
#define src x1
#define count x2
#define dst x3
#define srcend x4
#define dstend x5
#define A_l x6
#define A_lw w6
#define A_h x7
#define A_hw w7
#define B_l x8
#define B_lw w8
#define B_h x9
#define C_l x10
#define C_h x11
#define D_l x12
#define D_h x13
#define E_l x14
#define E_h x15
#define F_l x16
#define F_h x17
#define G_l count
#define G_h dst
#define H_l src
#define H_h srcend
#define tmp1 x14
/* This implementation of memcpy correctly handles overlaps, therefore
__memmove_aarch64 aliases to __memcpy_aarch64. By moving the src and
dst buffer overlap check from the start of memmove code to the
beginning of large copy code, the overhead of combining memcpy
and memmove implementations is negligible.
Copies are split into 3 main cases: small copies of up to 16 bytes,
medium copies of 17..128 bytes which are fully unrolled, and large
copies (moves).
Large forward moves align the destination and use an unrolled loop
processing 64 bytes per iteration.
Large backward moves align dstend and use an unrolled loop processing
64 bytes per iteration.
*/
ENTRY (__memcpy_aarch64)
ENTRY_ALIAS (__memmove_aarch64)
add srcend, src, count
add dstend, dstin, count
cmp count, 16
b.ls L(copy16)
cmp count, 128
b.hi L(move_long)
/* Medium copies: 17..128 bytes. */
ldp A_l, A_h, [src]
ldp D_l, D_h, [srcend, -16]
cmp count, 32
b.hi L(copy33_128)
stp A_l, A_h, [dstin]
stp D_l, D_h, [dstend, -16]
ret
.p2align 4
/* Small copies: 0..16 bytes. */
L(copy16):
/* 8-15 bytes. */
cmp count, 8
b.lo 1f
ldr A_l, [src]
ldr A_h, [srcend, -8]
str A_l, [dstin]
str A_h, [dstend, -8]
ret
.p2align 4
1:
/* 4-7 bytes. */
tbz count, 2, 1f
ldr A_lw, [src]
ldr A_hw, [srcend, -4]
str A_lw, [dstin]
str A_hw, [dstend, -4]
ret
.p2align 4
/* Copy 0..3 bytes. Use a branchless sequence that copies the same
byte 3 times if count==1, or the 2nd byte twice if count==2. */
1:
cbz count, 2f
lsr tmp1, count, 1
ldrb A_lw, [src]
ldrb A_hw, [srcend, -1]
ldrb B_lw, [src, tmp1]
strb A_lw, [dstin]
strb B_lw, [dstin, tmp1]
strb A_hw, [dstend, -1]
2: ret
.p2align 4
/* Copy 33..128 bytes. */
L(copy33_128):
ldp B_l, B_h, [src, 16]
ldp C_l, C_h, [srcend, -32]
cmp count, 64
b.hi L(copy65_128)
stp A_l, A_h, [dstin]
stp D_l, D_h, [dstend, -16]
stp B_l, B_h, [dstin, 16]
stp C_l, C_h, [dstend, -32]
ret
.p2align 4
/* Copy 65..128 bytes. */
L(copy65_128):
ldp E_l, E_h, [src, 32]
ldp F_l, F_h, [src, 48]
ldp G_l, G_h, [srcend, -64]
ldp H_l, H_h, [srcend, -48]
stp A_l, A_h, [dstin]
stp D_l, D_h, [dstend, -16]
stp B_l, B_h, [dstin, 16]
stp C_l, C_h, [dstend, -32]
stp E_l, E_h, [dstin, 32]
stp F_l, F_h, [dstin, 48]
stp G_l, G_h, [dstend, -64]
stp H_l, H_h, [dstend, -48]
ret
.p2align 4
/* Move more than 128 bytes. */
L(move_long):
sub tmp1, dstin, src /* Overlap check. */
cbz tmp1, L(copy0)
cmp tmp1, count
b.lo L(move_long_backwards)
/* Align dst to 16 byte alignment so that we don't cross cache line
boundaries on both loads and stores. There are at least 128 bytes
to copy, so copy 16 bytes unaligned and then align. The loop
copies 64 bytes per iteration and prefetches one iteration ahead. */
ldp D_l, D_h, [src]
and tmp1, dstin, 15
bic dst, dstin, 15
sub src, src, tmp1
add count, count, tmp1 /* Count is now 16 too large. */
ldp A_l, A_h, [src, 16]
stp D_l, D_h, [dstin]
ldp B_l, B_h, [src, 32]
ldp C_l, C_h, [src, 48]
ldp D_l, D_h, [src, 64]!
subs count, count, 128 + 16 /* Test and readjust count. */
b.ls L(copy64_from_end)
L(loop64):
stp A_l, A_h, [dst, 16]
ldp A_l, A_h, [src, 16]
stp B_l, B_h, [dst, 32]
ldp B_l, B_h, [src, 32]
stp C_l, C_h, [dst, 48]
ldp C_l, C_h, [src, 48]
stp D_l, D_h, [dst, 64]!
ldp D_l, D_h, [src, 64]!
subs count, count, 64
b.hi L(loop64)
/* Write the last full set of 64 bytes. The remainder is at most 64
bytes, so it is safe to always copy 64 bytes from the end even if
there is just 1 byte left. */
L(copy64_from_end):
ldp E_l, E_h, [srcend, -64]
stp A_l, A_h, [dst, 16]
ldp A_l, A_h, [srcend, -48]
stp B_l, B_h, [dst, 32]
ldp B_l, B_h, [srcend, -32]
stp C_l, C_h, [dst, 48]
ldp C_l, C_h, [srcend, -16]
stp D_l, D_h, [dst, 64]
stp E_l, E_h, [dstend, -64]
stp A_l, A_h, [dstend, -48]
stp B_l, B_h, [dstend, -32]
stp C_l, C_h, [dstend, -16]
L(copy0):
ret
.p2align 4
/* Move more than 128 bytes where src and dst buffers overlap
and dst > src.
Align dstend to 16 byte alignment so that we don't cross cache line
boundaries on both loads and stores. There are at least 128 bytes
to copy, so copy 16 bytes unaligned and then align. The loop
copies 64 bytes per iteration and prefetches one iteration ahead. */
L(move_long_backwards):
ldp D_l, D_h, [srcend, -16]
and tmp1, dstend, 15
sub srcend, srcend, tmp1
sub count, count, tmp1
ldp A_l, A_h, [srcend, -16]
stp D_l, D_h, [dstend, -16]
ldp B_l, B_h, [srcend, -32]
ldp C_l, C_h, [srcend, -48]
ldp D_l, D_h, [srcend, -64]!
sub dstend, dstend, tmp1
subs count, count, 128
b.ls L(copy64_from_start)
L(loop64_backwards):
stp A_l, A_h, [dstend, -16]
ldp A_l, A_h, [srcend, -16]
stp B_l, B_h, [dstend, -32]
ldp B_l, B_h, [srcend, -32]
stp C_l, C_h, [dstend, -48]
ldp C_l, C_h, [srcend, -48]
stp D_l, D_h, [dstend, -64]!
ldp D_l, D_h, [srcend, -64]!
subs count, count, 64
b.hi L(loop64_backwards)
/* Write the last full set of 64 bytes. The remainder is at most 64
bytes, so it is safe to always copy 64 bytes from the start even if
there is just 1 byte left. */
L(copy64_from_start):
ldp G_l, G_h, [src, 48]
stp A_l, A_h, [dstend, -16]
ldp A_l, A_h, [src, 32]
stp B_l, B_h, [dstend, -32]
ldp B_l, B_h, [src, 16]
stp C_l, C_h, [dstend, -48]
ldp C_l, C_h, [src]
stp D_l, D_h, [dstend, -64]
stp G_l, G_h, [dstin, 48]
stp A_l, A_h, [dstin, 32]
stp B_l, B_h, [dstin, 16]
stp C_l, C_h, [dstin]
ret
END (__memcpy_aarch64)
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