1/* $NetBSD: memcmp.S,v 1.3 2018/07/09 06:07:06 ryo Exp $ */
2
3/*-
4 * Copyright (c) 2014 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Matt Thomas of 3am Software Foundry.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29 * POSSIBILITY OF SUCH DAMAGE.
30 */
31
32#include <machine/asm.h>
33
34RCSID("$NetBSD: memcmp.S,v 1.3 2018/07/09 06:07:06 ryo Exp $")
35
36ENTRY(memcmp)
37	mov	x9, x0
38	mov	x10, x1
39	mov	x0, xzr
40	cbz	x2, .Lmemcmp_ret
41#ifdef _KERNEL
42	cmp	x2, #6
43	b.eq	.Lmemcmp_6bytes
44#endif
45	cmp	x2, #8
46	b.ls	.Lmemcmp_lessthan8
47
48	ands	x3, x9, #7
49	b.eq	.Lmemcmp_dword_loop
50
51/*
52 * The src1 address is not dword aligned.
53 */
54	add	x2, x2, x3		/* add unalignment to length */
55	sub	x2, x2, #8		/* now subtract a dword */
56
57	sub	x9, x9, x3		/* dword align src1 */
58
59	ldr	x6, [x10], #8		/* load dword from src2 */
60	sub	x10, x10, x3		/* src2 -= x3 */
61	lsl	x3, x3, #3		/* convert bytes to bits */
62	ldr	x4, [x9], #8		/* load dword from src1 */
63#ifdef __AARCH64EB__
64	lsl	x4, x4, x3		/* discard leading bytes from data1 */
65	lsr	x6, x6, x3		/* discard leading bytes from data2 */
66	lsl	x6, x6, x3		/* get back bit position */
67#else
68	lsr	x4, x4, x3		/* discard leading bytes from data1 */
69	lsl	x6, x6, x3		/* discard leading bytes from data2 */
70	lsr	x6, x6, x3		/* get back bit position */
71#endif
72	subs	x0, x4, x6		/* compare data */
73	b.ne	.Lmemcmp_last_compare	/* difference.  find it */
74
75.Lmemcmp_dword_loop:
76	subs	x2, x2, #8
77	b.mi	.Lmemcmp_finish_dword
78	ldr	x4, [x9], #8
79	ldr	x6, [x10], #8
80	subs	x0, x4, x6
81	b.eq	.Lmemcmp_dword_loop	/* no difference.  go to loop */
82	b	.Lmemcmp_last_compare	/* go find the difference. */
83
84.Lmemcmp_finish_dword:
85	/*
86	 * we might have gotten here with nothing left.  If so, just bail.
87	 */
88	tst	x2, #7
89	b.eq	.Lmemcmp_ret
90	mov	x4, xzr
91	mov	x6, xzr
92	/*
93	 *
94	 */
95	tbz	x2, #2, .Lmemcmp_finish_word
96	ldr	w4, [x9], #4
97	ldr	w6, [x10], #4
98#ifdef __AARCH64EB__
99	lsl	x4, x4, #32		/* move to MSW */
100	lsl	x6, x6, #32		/* move to MSW */
101#endif
102
103.Lmemcmp_finish_word:
104	tbz	x2, #1, .Lmemcmp_finish_hword
105	ldrh	w5, [x9], #2
106	ldrh	w7, [x10], #2
107#ifdef __AARCH64EB__
108	orr	x4, x4, x5, lsl #16
109	orr	x6, x6, x7, lsl #16
110#else
111	orr	x4, x4, x5, lsl #32
112	orr	x6, x6, x7, lsl #32
113#endif
114
115.Lmemcmp_finish_hword:
116	tbz	x2, #0, .Lmemcmp_last_compare0
117
118	ldrb	w5, [x9]
119	ldrb	w7, [x10]
120#ifdef __AARCH64EB__
121	orr	x4, x4, x5, lsl #8
122	orr	x6, x6, x7, lsl #8
123#else
124	orr	x4, x4, x5, lsl #48
125	orr	x6, x6, x7, lsl #48
126#endif
127	b	.Lmemcmp_last_compare0	/* go find the difference. */
128
129/*
130 * D
131 */
132.Lmemcmp_lessthan8:
133	sub	x2, x2, #1
1341:	ldrb	w4, [x9], #1
135	ldrb	w5, [x10], #1
136	subs	x2, x2, #1
137	ccmp	x4, x5, #0, cs
138	b.eq	1b
139	sub	x0, x4, x5
140
141.Lmemcmp_ret:
142	ret
143
144#ifdef _KERNEL
145.Lmemcmp_6bytes:
146	ldr	w4, [x9], #4
147	ldrh	w5, [x9]
148#if __AARCH64EB__
149	orr	x4, x4, x5, lsl #48
150	rev	x4, x4
151#else
152	orr	x4, x4, x5, lsl #32
153#endif
154	ldr	w6, [x10], #4
155	ldrh	w7, [x10]
156#if __AARCH64EB__
157	orr	x6, x6, x7, lsl #48
158	rev	x6, x6
159#else
160	orr	x6, x6, x7, lsl #32
161#endif
162#endif /* _KERNEL */
163
164/*
165 * We have loaded the final bytes in x4 and x6 in host-endian.  Now we have
166 * to figure what the difference is (if any).  First we subtract.  Any bytes
167 * that are the same will be 0. So to find the first non-zero byte we byterev
168 * and then use clz to find that byte.
169 * We mask the location to get the start of the byte.  We shift both
170 * data dwords left to remove the equal part.  Then we shift right to discard
171 * the trailing bytes.  Then we subtract and return.
172 */
173.Lmemcmp_last_compare0:
174	subs	x0, x4, x6
175	b.eq	.Lmemcmp_ret
176.Lmemcmp_last_compare:
177#if __AARCH64EB__
178	clz	x1, x0		/* find first non-zero byte */
179	rev	x0, x0
180#else
181	rev	x1, x0
182	clz	x1, x1		/* find first non-zero byte */
183#endif
184	bfi	x1, xzr, #0, #3 /* make it byte aligned */
185	lsr	x1, x0, x1	/* shift to LSB */
186#if __AARCH64EL__
187	rev	x4, x4		/* byte reverse */
188	rev	x6, x6		/* byte reverse */
189#endif
190	subs	x0, x4, x6
191	csetm	x0, cc		/* set mask bits as sign */
192	bfm	x0, x1, #0, #7	/* extend with sign bit */
193	ret
194END(memcmp)
195