summaryrefslogtreecommitdiff
path: root/sysdeps/arm/armv6/strchr.S
blob: f6fd192144a47b65a48bcb75c2366becc4c5325a (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
/* strchr -- find the first instance of C in a nul-terminated string.
   Copyright (C) 2013-2017 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>

	.syntax unified
	.text

ENTRY (strchr)
	@ r0 = start of string
	@ r1 = character to match
	@ returns NULL for no match, or a pointer to the match
	sfi_breg r0, \
	ldrb	r2, [\B]		@ load the first byte asap
	uxtb	r1, r1

	@ To cater to long strings, we want to search through a few
	@ characters until we reach an aligned pointer.  To cater to
	@ small strings, we don't want to start doing word operations
	@ immediately.  The compromise is a maximum of 16 bytes less
	@ whatever is required to end with an aligned pointer.
	@ r3 = number of characters to search in alignment loop
	and	r3, r0, #7
	rsb	r3, r3, #15		@ 16 - 1 peeled loop iteration
	cmp	r2, r1			@ Found C?
	it	ne
	cmpne	r2, #0			@ Found EOS?
	beq	99f

	@ Loop until we find ...
1:	sfi_breg r0, \
	ldrb	r2, [\B, #1]!
	subs	r3, r3, #1		@ ... the aligment point
	it	ne
	cmpne	r2, r1			@ ... or the character
	it	ne
	cmpne	r2, #0			@ ... or EOS
	bne	1b

	@ Disambiguate the exit possibilites above
	cmp	r2, r1			@ Found the character
	it	ne
	cmpne	r2, #0			@ Found EOS
	beq	99f
	add	r0, r0, #1

	@ So now we're aligned.  Now we actually need a stack frame.
	push	{ r4, r5, r6, r7 }
	cfi_adjust_cfa_offset (16)
	cfi_rel_offset (r4, 0)
	cfi_rel_offset (r5, 4)
	cfi_rel_offset (r6, 8)
	cfi_rel_offset (r7, 12)

	sfi_breg r0, \
	ldrd	r2, r3, [\B], #8
	orr	r1, r1, r1, lsl #8	@ Replicate C to all bytes
#ifdef ARCH_HAS_T2
	movw	ip, #0x0101
	sfi_pld	r0, #64
	movt	ip, #0x0101
#else
	ldr	ip, =0x01010101
	sfi_pld	r0, #64
#endif
	orr	r1, r1, r1, lsl #16

	@ Loop searching for EOS or C, 8 bytes at a time.
2:
	@ Subtracting (unsigned saturating) from 1 means result of 1 for
	@ any byte that was originally zero and 0 otherwise.  Therefore
	@ we consider the lsb of each byte the "found" bit.
	uqsub8	r4, ip, r2		@ Find EOS
	eor	r6, r2, r1		@ Convert C bytes to 0
	uqsub8	r5, ip, r3
	eor	r7, r3, r1
	uqsub8	r6, ip, r6		@ Find C
	sfi_pld	r0, #128		@ Prefetch 2 lines ahead
	uqsub8	r7, ip, r7
	orr	r4, r4, r6		@ Combine found for EOS and C
	orr	r5, r5, r7
	orrs	r6, r4, r5		@ Combine the two words
	it	eq
	sfi_breg r0, \
	ldrdeq	r2, r3, [\B], #8
	beq	2b

	@ Found something.  Disambiguate between first and second words.
	@ Adjust r0 to point to the word containing the match.
	@ Adjust r2 to the contents of the word containing the match.
	@ Adjust r4 to the found bits for the word containing the match.
	cmp	r4, #0
	sub	r0, r0, #4
	itte	eq
	moveq	r4, r5
	moveq	r2, r3
	subne	r0, r0, #4

	@ Find the bit-offset of the match within the word.
#if defined(__ARMEL__)
	@ For LE, swap the found word so clz searches from the little end.
	rev	r4, r4
#else
	@ For BE, byte swap the word to make it easier to extract the byte.
	rev	r2, r2
#endif
	@ We're counting 0x01 (not 0x80), so the bit offset is 7 too high.
	clz	r3, r4
	sub	r3, r3, #7
	lsr	r2, r2, r3		@ Shift down found byte
	uxtb	r1, r1			@ Undo replication of C
	uxtb	r2, r2			@ Extract found byte
	add	r0, r0, r3, lsr #3	@ Adjust the pointer to the found byte

	pop	{ r4, r5, r6, r7 }
	cfi_adjust_cfa_offset (-16)
	cfi_restore (r4)
	cfi_restore (r5)
	cfi_restore (r6)
	cfi_restore (r7)

	@ Disambiguate between EOS and C.
99:
	cmp	r2, r1
	it	ne
	movne	r0, #0			@ Found EOS, return NULL
	bx	lr

END (strchr)

weak_alias (strchr, index)
libc_hidden_builtin_def (strchr)