1/* strrchr -- find the last occurence of C in a nul-terminated string
2   Copyright (C) 2013-2022 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 (strrchr)
25	@ r0 = start of string
26	@ r1 = character to match
27	@ returns NULL for no match, or a pointer to the match
28
29	mov	r3, r0
30	mov	r0, #0
31	uxtb	r1, r1
32
33	@ Loop a few times until we're aligned.
34	tst	r3, #7
35	beq	2f
361:	ldrb	r2, [r3], #1
37	cmp	r2, r1			@ Find the character
38	it	eq
39	subeq	r0, r3, #1
40	cmp	r2, #0			@ Find EOS
41	it	eq
42	bxeq	lr
43	tst	r3, #7			@ Find the aligment point
44	bne	1b
45
46	@ So now we're aligned.  Now we actually need a stack frame.
472:	push	{ r4, r5, r6, r7 }
48	cfi_adjust_cfa_offset (16)
49	cfi_rel_offset (r4, 0)
50	cfi_rel_offset (r5, 4)
51	cfi_rel_offset (r6, 8)
52	cfi_rel_offset (r7, 12)
53
54	orr	r1, r1, r1, lsl #8	@ Replicate C to all bytes
55#ifdef ARCH_HAS_T2
56	movw	ip, #0x0101
57	movt	ip, #0x0101
58#else
59	ldr	ip, =0x01010101
60#endif
61	orr	r1, r1, r1, lsl #16
62	mov	r2, #0			@ No found bits yet
63
64	@ Loop searching for EOS and C, 8 bytes at a time.
65	@ Any time we find a match in a word, we copy the address of
66	@ the word to r0, and the found bits to r2.
673:	ldrd	r4, r5, [r3], #8
68	@ Subtracting (unsigned saturating) from 1 means result of 1 for
69	@ any byte that was originally zero and 0 otherwise.  Therefore
70	@ we consider the lsb of each byte the "found" bit.
71	uqsub8	r6, ip, r4		@ Find EOS
72	uqsub8	r7, ip, r5
73	eor	r4, r4, r1		@ Convert C bytes to 0
74	eor	r5, r5, r1
75	uqsub8	r4, ip, r4		@ Find C
76	uqsub8	r5, ip, r5
77	cmp	r6, #0			@ Found EOS, first word
78	bne	4f
79	cmp	r4, #0			@ Handle C, first word
80	itt	ne
81	subne	r0, r3, #8
82	movne	r2, r4
83	cmp	r7, #0			@ Found EOS, second word
84	bne	5f
85	cmp	r5, #0			@ Handle C, second word
86	itt	ne
87	subne	r0, r3, #4
88	movne	r2, r5
89	b	3b
90
91	@ Found EOS in second word; fold to first word.
925:	add	r3, r3, #4		@ Dec pointer to 2nd word, with below
93	mov	r4, r5			@ Overwrite first word C found
94	mov	r6, r7			@ Overwrite first word EOS found
95
96	@ Found EOS.  Zap found C after EOS.
974:	sub	r3, r3, #8		@ Decrement pointer to first word
98#ifdef __ARMEB__
99	@ Byte swap to be congruent with LE, which is easier from here on.
100	rev	r6, r6			@ Byte swap found EOS,
101	rev	r4, r4			@ ... this found C
102	rev	r2, r2			@ ... prev found C
103#endif
104	sub	r7, r6, #1		@ Toggle EOS lsb and below
105	eor	r6, r6, r7		@ All bits below and including lsb
106	ands	r4, r4, r6		@ Zap C above EOS
107	itt	ne
108	movne	r2, r4			@ Copy to result, if still non-zero
109	movne	r0, r3
110
111	pop	{ r4, r5, r6, r7 }
112	cfi_adjust_cfa_offset (-16)
113	cfi_restore (r4)
114	cfi_restore (r5)
115	cfi_restore (r6)
116	cfi_restore (r7)
117
118	@ Adjust the result pointer if we found a word containing C.
119	cmp	r2, #0
120	clz	r2, r2			@ Find the bit offset of the last C
121	itt	ne
122	rsbne	r2, r2, #32		@ Convert to a count from the right
123	addne	r0, r0, r2, lsr #3	@ Convert to byte offset and add.
124	bx	lr
125
126END (strrchr)
127
128weak_alias (strrchr, rindex)
129libc_hidden_builtin_def (strrchr)
130