glibc/sysdeps/aarch64/memcmp.S

/* memcmp - compare memory

   Copyright (C) 2013-2019 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library.  If not, see
   <http://www.gnu.org/licenses/>.  */

#include <sysdep.h>

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

/* Parameters and result.  */
#define src1		x0
#define src2		x1
#define limit		x2
#define result		w0

/* Internal variables.  */
#define data1		x3
#define data1w		w3
#define data1h		x4
#define data2		x5
#define data2w		w5
#define data2h		x6
#define tmp1		x7
#define tmp2		x8

ENTRY_ALIGN (memcmp, 6)
	DELOUSE (0)
	DELOUSE (1)
	DELOUSE (2)

	subs	limit, limit, 8
	b.lo	L(less8)

	ldr	data1, [src1], 8
	ldr	data2, [src2], 8
	cmp	data1, data2
	b.ne	L(return)

	subs	limit, limit, 8
	b.gt	L(more16)

	ldr	data1, [src1, limit]
	ldr	data2, [src2, limit]
	b	L(return)

L(more16):
	ldr	data1, [src1], 8
	ldr	data2, [src2], 8
	cmp	data1, data2
	bne	L(return)

	/* Jump directly to comparing the last 16 bytes for 32 byte (or less)
	   strings.  */
	subs	limit, limit, 16
	b.ls	L(last_bytes)

	/* We overlap loads between 0-32 bytes at either side of SRC1 when we
	   try to align, so limit it only to strings larger than 128 bytes.  */
	cmp	limit, 96
	b.ls	L(loop16)

	/* Align src1 and adjust src2 with bytes not yet done.  */
	and	tmp1, src1, 15
	add	limit, limit, tmp1
	sub	src1, src1, tmp1
	sub	src2, src2, tmp1

	/* Loop performing 16 bytes per iteration using aligned src1.
	   Limit is pre-decremented by 16 and must be larger than zero.
	   Exit if <= 16 bytes left to do or if the data is not equal.  */
	.p2align 4
L(loop16):
	ldp	data1, data1h, [src1], 16
	ldp	data2, data2h, [src2], 16
	subs	limit, limit, 16
	ccmp	data1, data2, 0, hi
	ccmp	data1h, data2h, 0, eq
	b.eq	L(loop16)

	cmp	data1, data2
	bne	L(return)
	mov	data1, data1h
	mov	data2, data2h
	cmp	data1, data2
	bne	L(return)

	/* Compare last 1-16 bytes using unaligned access.  */
L(last_bytes):
	add	src1, src1, limit
	add	src2, src2, limit
	ldp	data1, data1h, [src1]
	ldp	data2, data2h, [src2]
	cmp     data1, data2
	bne	L(return)
	mov	data1, data1h
	mov	data2, data2h
	cmp	data1, data2

	/* Compare data bytes and set return value to 0, -1 or 1.  */
L(return):
#ifndef __AARCH64EB__
	rev	data1, data1
	rev	data2, data2
#endif
	cmp     data1, data2
L(ret_eq):
	cset	result, ne
	cneg	result, result, lo
	ret

	.p2align 4
	/* Compare up to 8 bytes.  Limit is [-8..-1].  */
L(less8):
	adds	limit, limit, 4
	b.lo	L(less4)
	ldr	data1w, [src1], 4
	ldr	data2w, [src2], 4
	cmp	data1w, data2w
	b.ne	L(return)
	sub	limit, limit, 4
L(less4):
	adds	limit, limit, 4
	beq	L(ret_eq)
L(byte_loop):
	ldrb	data1w, [src1], 1
	ldrb	data2w, [src2], 1
	subs	limit, limit, 1
	ccmp	data1w, data2w, 0, ne	/* NZCV = 0b0000.  */
	b.eq	L(byte_loop)
	sub	result, data1w, data2w
	ret

END (memcmp)
#undef bcmp
weak_alias (memcmp, bcmp)
libc_hidden_builtin_def (memcmp)