1/* strchr -- find the first instance of C in a nul-terminated string.
2   Copyright (C) 2013-2021 Free Software Foundation, Inc.
3   This file is part of the GNU C Library.
4
5   The GNU C Library is free software; you can redistribute it and/or
6   modify it under the terms of the GNU Lesser General Public
7   License as published by the Free Software Foundation; either
8   version 2.1 of the License, or (at your option) any later version.
9
10   The GNU C Library is distributed in the hope that it will be useful,
11   but WITHOUT ANY WARRANTY; without even the implied warranty of
12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13   Lesser General Public License for more details.
14
15   You should have received a copy of the GNU Lesser General Public
16   License along with the GNU C Library.  If not, see
17   <https://www.gnu.org/licenses/>.  */
18
19#include <sysdep.h>
20
21	.syntax unified
22	.text
23
24ENTRY (strchr)
25	@ r0 = start of string
26	@ r1 = character to match
27	@ returns NULL for no match, or a pointer to the match
28	ldrb	r2, [r0]		@ load the first byte asap
29	uxtb	r1, r1
30
31	@ To cater to long strings, we want to search through a few
32	@ characters until we reach an aligned pointer.  To cater to
33	@ small strings, we don't want to start doing word operations
34	@ immediately.  The compromise is a maximum of 16 bytes less
35	@ whatever is required to end with an aligned pointer.
36	@ r3 = number of characters to search in alignment loop
37	and	r3, r0, #7
38	rsb	r3, r3, #15		@ 16 - 1 peeled loop iteration
39	cmp	r2, r1			@ Found C?
40	it	ne
41	cmpne	r2, #0			@ Found EOS?
42	beq	99f
43
44	@ Loop until we find ...
451:	ldrb	r2, [r0, #1]!
46	subs	r3, r3, #1		@ ... the aligment point
47	it	ne
48	cmpne	r2, r1			@ ... or the character
49	it	ne
50	cmpne	r2, #0			@ ... or EOS
51	bne	1b
52
53	@ Disambiguate the exit possibilites above
54	cmp	r2, r1			@ Found the character
55	it	ne
56	cmpne	r2, #0			@ Found EOS
57	beq	99f
58	add	r0, r0, #1
59
60	@ So now we're aligned.  Now we actually need a stack frame.
61	push	{ r4, r5, r6, r7 }
62	cfi_adjust_cfa_offset (16)
63	cfi_rel_offset (r4, 0)
64	cfi_rel_offset (r5, 4)
65	cfi_rel_offset (r6, 8)
66	cfi_rel_offset (r7, 12)
67
68	ldrd	r2, r3, [r0], #8
69	orr	r1, r1, r1, lsl #8	@ Replicate C to all bytes
70#ifdef ARCH_HAS_T2
71	movw	ip, #0x0101
72	pld	[r0, #64]
73	movt	ip, #0x0101
74#else
75	ldr	ip, =0x01010101
76	pld	[r0, #64]
77#endif
78	orr	r1, r1, r1, lsl #16
79
80	@ Loop searching for EOS or C, 8 bytes at a time.
812:
82	@ Subtracting (unsigned saturating) from 1 means result of 1 for
83	@ any byte that was originally zero and 0 otherwise.  Therefore
84	@ we consider the lsb of each byte the "found" bit.
85	uqsub8	r4, ip, r2		@ Find EOS
86	eor	r6, r2, r1		@ Convert C bytes to 0
87	uqsub8	r5, ip, r3
88	eor	r7, r3, r1
89	uqsub8	r6, ip, r6		@ Find C
90	pld	[r0, #128]		@ Prefetch 2 lines ahead
91	uqsub8	r7, ip, r7
92	orr	r4, r4, r6		@ Combine found for EOS and C
93	orr	r5, r5, r7
94	orrs	r6, r4, r5		@ Combine the two words
95	it	eq
96	ldrdeq	r2, r3, [r0], #8
97	beq	2b
98
99	@ Found something.  Disambiguate between first and second words.
100	@ Adjust r0 to point to the word containing the match.
101	@ Adjust r2 to the contents of the word containing the match.
102	@ Adjust r4 to the found bits for the word containing the match.
103	cmp	r4, #0
104	sub	r0, r0, #4
105	itte	eq
106	moveq	r4, r5
107	moveq	r2, r3
108	subne	r0, r0, #4
109
110	@ Find the bit-offset of the match within the word.
111#if defined(__ARMEL__)
112	@ For LE, swap the found word so clz searches from the little end.
113	rev	r4, r4
114#else
115	@ For BE, byte swap the word to make it easier to extract the byte.
116	rev	r2, r2
117#endif
118	@ We're counting 0x01 (not 0x80), so the bit offset is 7 too high.
119	clz	r3, r4
120	sub	r3, r3, #7
121	lsr	r2, r2, r3		@ Shift down found byte
122	uxtb	r1, r1			@ Undo replication of C
123	uxtb	r2, r2			@ Extract found byte
124	add	r0, r0, r3, lsr #3	@ Adjust the pointer to the found byte
125
126	pop	{ r4, r5, r6, r7 }
127	cfi_adjust_cfa_offset (-16)
128	cfi_restore (r4)
129	cfi_restore (r5)
130	cfi_restore (r6)
131	cfi_restore (r7)
132
133	@ Disambiguate between EOS and C.
13499:
135	cmp	r2, r1
136	it	ne
137	movne	r0, #0			@ Found EOS, return NULL
138	bx	lr
139
140END (strchr)
141
142weak_alias (strchr, index)
143libc_hidden_builtin_def (strchr)
144