summaryrefslogtreecommitdiff
path: root/arch/arm64/lib/strnlen.S
blob: e21e536d420e96e110d0c03512f27b6752a91ee5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
/*
 * Copyright (C) 2013 ARM Ltd.
 * Copyright (C) 2013 Linaro.
 *
 * This code is based on glibc cortex strings work originally authored by Linaro
 * and re-licensed under GPLv2 for the Linux kernel. The original code can
 * be found @
 *
 * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
 * files/head:/src/aarch64/
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <linux/linkage.h>
#include <asm/assembler.h>

/*
 * determine the length of a fixed-size string
 *
 * Parameters:
 *	x0 - const string pointer
 *	x1 - maximal string length
 * Returns:
 *	x0 - the return length of specific string
 */

/* Arguments and results.  */
srcin		.req	x0
len		.req	x0
limit		.req	x1

/* Locals and temporaries.  */
src		.req	x2
data1		.req	x3
data2		.req	x4
data2a		.req	x5
has_nul1	.req	x6
has_nul2	.req	x7
tmp1		.req	x8
tmp2		.req	x9
tmp3		.req	x10
tmp4		.req	x11
zeroones	.req	x12
pos		.req	x13
limit_wd	.req	x14

#define REP8_01 0x0101010101010101
#define REP8_7f 0x7f7f7f7f7f7f7f7f
#define REP8_80 0x8080808080808080

WEAK(strnlen)
	cbz	limit, .Lhit_limit
	mov	zeroones, #REP8_01
	bic	src, srcin, #15
	ands	tmp1, srcin, #15
	b.ne	.Lmisaligned
	/* Calculate the number of full and partial words -1.  */
	sub	limit_wd, limit, #1 /* Limit != 0, so no underflow.  */
	lsr	limit_wd, limit_wd, #4  /* Convert to Qwords.  */

	/*
	* NUL detection works on the principle that (X - 1) & (~X) & 0x80
	* (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
	* can be done in parallel across the entire word.
	*/
	/*
	* The inner loop deals with two Dwords at a time.  This has a
	* slightly higher start-up cost, but we should win quite quickly,
	* especially on cores with a high number of issue slots per
	* cycle, as we get much better parallelism out of the operations.
	*/
.Lloop:
	ldp	data1, data2, [src], #16
.Lrealigned:
	sub	tmp1, data1, zeroones
	orr	tmp2, data1, #REP8_7f
	sub	tmp3, data2, zeroones
	orr	tmp4, data2, #REP8_7f
	bic	has_nul1, tmp1, tmp2
	bic	has_nul2, tmp3, tmp4
	subs	limit_wd, limit_wd, #1
	orr	tmp1, has_nul1, has_nul2
	ccmp	tmp1, #0, #0, pl    /* NZCV = 0000  */
	b.eq	.Lloop

	cbz	tmp1, .Lhit_limit   /* No null in final Qword.  */

	/*
	* We know there's a null in the final Qword. The easiest thing
	* to do now is work out the length of the string and return
	* MIN (len, limit).
	*/
	sub	len, src, srcin
	cbz	has_nul1, .Lnul_in_data2
CPU_BE( mov	data2, data1 )	/*perpare data to re-calculate the syndrome*/

	sub	len, len, #8
	mov	has_nul2, has_nul1
.Lnul_in_data2:
	/*
	* For big-endian, carry propagation (if the final byte in the
	* string is 0x01) means we cannot use has_nul directly.  The
	* easiest way to get the correct byte is to byte-swap the data
	* and calculate the syndrome a second time.
	*/
CPU_BE( rev	data2, data2 )
CPU_BE( sub	tmp1, data2, zeroones )
CPU_BE( orr	tmp2, data2, #REP8_7f )
CPU_BE( bic	has_nul2, tmp1, tmp2 )

	sub	len, len, #8
	rev	has_nul2, has_nul2
	clz	pos, has_nul2
	add	len, len, pos, lsr #3       /* Bits to bytes.  */
	cmp	len, limit
	csel	len, len, limit, ls     /* Return the lower value.  */
	ret

.Lmisaligned:
	/*
	* Deal with a partial first word.
	* We're doing two things in parallel here;
	* 1) Calculate the number of words (but avoiding overflow if
	* limit is near ULONG_MAX) - to do this we need to work out
	* limit + tmp1 - 1 as a 65-bit value before shifting it;
	* 2) Load and mask the initial data words - we force the bytes
	* before the ones we are interested in to 0xff - this ensures
	* early bytes will not hit any zero detection.
	*/
	ldp	data1, data2, [src], #16

	sub	limit_wd, limit, #1
	and	tmp3, limit_wd, #15
	lsr	limit_wd, limit_wd, #4

	add	tmp3, tmp3, tmp1
	add	limit_wd, limit_wd, tmp3, lsr #4

	neg	tmp4, tmp1
	lsl	tmp4, tmp4, #3  /* Bytes beyond alignment -> bits.  */

	mov	tmp2, #~0
	/* Big-endian.  Early bytes are at MSB.  */
CPU_BE( lsl	tmp2, tmp2, tmp4 )	/* Shift (tmp1 & 63).  */
	/* Little-endian.  Early bytes are at LSB.  */
CPU_LE( lsr	tmp2, tmp2, tmp4 )	/* Shift (tmp1 & 63).  */

	cmp	tmp1, #8

	orr	data1, data1, tmp2
	orr	data2a, data2, tmp2

	csinv	data1, data1, xzr, le
	csel	data2, data2, data2a, le
	b	.Lrealigned

.Lhit_limit:
	mov	len, limit
	ret
ENDPIPROC(strnlen)
EXPORT_SYMBOL_NOKASAN(strnlen)