1/* strlen -- find the length of 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 (strlen)
25	@ r0 = start of string
26	ldrb	r2, [r0]		@ load the first byte asap
27
28	@ To cater to long strings, we want to search through a few
29	@ characters until we reach an aligned pointer.  To cater to
30	@ small strings, we don't want to start doing word operations
31	@ immediately.  The compromise is a maximum of 16 bytes less
32	@ whatever is required to end with an aligned pointer.
33	@ r3 = number of characters to search in alignment loop
34	and	r3, r0, #7
35	mov	r1, r0			@ Save the input pointer
36	rsb	r3, r3, #15		@ 16 - 1 peeled loop iteration
37	cmp	r2, #0
38	beq	99f
39
40	@ Loop until we find ...
411:	ldrb	r2, [r0, #1]!
42	subs	r3, r3, #1		@ ... the aligment point
43	it	ne
44	cmpne	r2, #0			@ ... or EOS
45	bne	1b
46
47	@ Disambiguate the exit possibilites above
48	cmp	r2, #0			@ Found EOS
49	beq	99f
50	add	r0, r0, #1
51
52	@ So now we're aligned.
53	ldrd	r2, r3, [r0], #8
54#ifdef ARCH_HAS_T2
55	movw	ip, #0x0101
56	pld	[r0, #64]
57	movt	ip, #0x0101
58#else
59	ldr	ip, =0x01010101
60	pld	[r0, #64]
61#endif
62
63	@ Loop searching for EOS, 8 bytes at a time.
64	@ Subtracting (unsigned saturating) from 1 for any byte means that
65	@ we get 1 for any byte that was originally zero and 0 otherwise.
66	@ Therefore we consider the lsb of each byte the "found" bit.
67	.balign	16
682:	uqsub8	r2, ip, r2		@ Find EOS
69	uqsub8	r3, ip, r3
70	pld	[r0, #128]		@ Prefetch 2 lines ahead
71	orrs	r3, r3, r2		@ Combine the two words
72	it	eq
73	ldrdeq	r2, r3, [r0], #8
74	beq	2b
75
76	@ Found something.  Disambiguate between first and second words.
77	@ Adjust r0 to point to the word containing the match.
78	@ Adjust r2 to the found bits for the word containing the match.
79	cmp	r2, #0
80	sub	r0, r0, #4
81	ite	eq
82	moveq	r2, r3
83	subne	r0, r0, #4
84
85	@ Find the bit-offset of the match within the word.  Note that the
86	@ bit result from clz will be 7 higher than "true", but we'll
87	@ immediately discard those bits converting to a byte offset.
88#ifdef __ARMEL__
89	rev	r2, r2			@ For LE, count from the little end
90#endif
91	clz	r2, r2
92	add	r0, r0, r2, lsr #3	@ Adjust the pointer to the found byte
9399:
94	sub	r0, r0, r1		@ Subtract input to compute length
95	bx	lr
96
97END (strlen)
98
99libc_hidden_builtin_def (strlen)
100