src/string/aarch64/memcpy.S

/*
 * memcpy - copy memory area
 *
 * Copyright (c) 2012-2020, Arm Limited.
 * SPDX-License-Identifier: MIT
 */

/* Assumptions:
 *
 * ARMv8-a, AArch64, unaligned accesses.
 *
 */

#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 B_l     x8
#define B_lw    w8
#define B_h     x9
#define C_l     x10
#define C_lw    w10
#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 uses unaligned accesses and branchless
   sequences to keep the code small, simple and improve performance.

   Copies are split into 3 main cases: small copies of up to 32 bytes, medium
   copies of up to 128 bytes, and large copies.  The overhead of the overlap
   check is negligible since it is only required for large copies.

   Large copies use a software pipelined loop processing 64 bytes per iteration.
   The destination pointer is 16-byte aligned to minimize unaligned accesses.
   The loop tail is handled by always copying 64 bytes from the end.
*/

.global memcpy
.type memcpy,%function
memcpy:
	add     srcend, src, count
	add     dstend, dstin, count
	cmp     count, 128
	b.hi    .Lcopy_long
	cmp     count, 32
	b.hi    .Lcopy32_128

	/* Small copies: 0..32 bytes.  */
	cmp     count, 16
	b.lo    .Lcopy16
	ldp     A_l, A_h, [src]
	ldp     D_l, D_h, [srcend, -16]
	stp     A_l, A_h, [dstin]
	stp     D_l, D_h, [dstend, -16]
	ret

	/* Copy 8-15 bytes.  */
.Lcopy16:
	tbz     count, 3, .Lcopy8
	ldr     A_l, [src]
	ldr     A_h, [srcend, -8]
	str     A_l, [dstin]
	str     A_h, [dstend, -8]
	ret

	.p2align 3
	/* Copy 4-7 bytes.  */
.Lcopy8:
	tbz     count, 2, .Lcopy4
	ldr     A_lw, [src]
	ldr     B_lw, [srcend, -4]
	str     A_lw, [dstin]
	str     B_lw, [dstend, -4]
	ret

	/* Copy 0..3 bytes using a branchless sequence.  */
.Lcopy4:
	cbz     count, .Lcopy0
	lsr     tmp1, count, 1
	ldrb    A_lw, [src]
	ldrb    C_lw, [srcend, -1]
	ldrb    B_lw, [src, tmp1]
	strb    A_lw, [dstin]
	strb    B_lw, [dstin, tmp1]
	strb    C_lw, [dstend, -1]
.Lcopy0:
	ret

	.p2align 4
	/* Medium copies: 33..128 bytes.  */
.Lcopy32_128:
	ldp     A_l, A_h, [src]
	ldp     B_l, B_h, [src, 16]
	ldp     C_l, C_h, [srcend, -32]
	ldp     D_l, D_h, [srcend, -16]
	cmp     count, 64
	b.hi    .Lcopy128
	stp     A_l, A_h, [dstin]
	stp     B_l, B_h, [dstin, 16]
	stp     C_l, C_h, [dstend, -32]
	stp     D_l, D_h, [dstend, -16]
	ret

	.p2align 4
	/* Copy 65..128 bytes.  */
.Lcopy128:
	ldp     E_l, E_h, [src, 32]
	ldp     F_l, F_h, [src, 48]
	cmp     count, 96
	b.ls    .Lcopy96
	ldp     G_l, G_h, [srcend, -64]
	ldp     H_l, H_h, [srcend, -48]
	stp     G_l, G_h, [dstend, -64]
	stp     H_l, H_h, [dstend, -48]
.Lcopy96:
	stp     A_l, A_h, [dstin]
	stp     B_l, B_h, [dstin, 16]
	stp     E_l, E_h, [dstin, 32]
	stp     F_l, F_h, [dstin, 48]
	stp     C_l, C_h, [dstend, -32]
	stp     D_l, D_h, [dstend, -16]
	ret

	.p2align 4
	/* Copy more than 128 bytes.  */
.Lcopy_long:

	/* Copy 16 bytes and then align dst to 16-byte alignment.  */

	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    .Lcopy64_from_end

.Lloop64:
	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    .Lloop64

	/* Write the last iteration and copy 64 bytes from the end.  */
.Lcopy64_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]
	ret

.size memcpy,.-memcpy