1/* Copyright (C) 2011-2024 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library. If not, see
16 <https://www.gnu.org/licenses/>. */
17
18#include <sysdep.h>
19
20@ This memchr routine is optimised on a Cortex-A9 and should work on all ARMv7
21@ and ARMv6T2 processors. It has a fast path for short sizes, and has an
22@ optimised path for large data sets; the worst case is finding the match early
23@ in a large data set.
24@ Note: The use of cbz/cbnz means it's Thumb only
25
26@ 2011-07-15 david.gilbert@linaro.org
27@ Copy from Cortex strings release 21 and change license
28@ http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/view/head:/src/linaro-a9/memchr.S
29@ Change function declarations/entry/exit
30@ 2011-12-01 david.gilbert@linaro.org
31@ Add some fixes from comments received (including use of ldrd instead ldm)
32@ 2011-12-07 david.gilbert@linaro.org
33@ Removed cbz from align loop - can't be taken
34
35@ this lets us check a flag in a 00/ff byte easily in either endianness
36#ifdef __ARMEB__
37#define CHARTSTMASK(c) 1<<(31-(c*8))
38#else
39#define CHARTSTMASK(c) 1<<(c*8)
40#endif
41 .syntax unified
42
43 .text
44 .thumb
45 .thumb_func
46 .global memchr
47 .type memchr,%function
48ENTRY(memchr)
49 @ r0 = start of memory to scan
50 @ r1 = character to look for
51 @ r2 = length
52 @ returns r0 = pointer to character or NULL if not found
53 and r1,r1,#0xff @ Don't think we can trust the caller to actually pass a char
54
55 cmp r2,#16 @ If it's short don't bother with anything clever
56 blt 20f
57
58 tst r0, #7 @ If it's already aligned skip the next bit
59 beq 10f
60
61 @ Work up to an aligned point
625:
63 ldrb r3, [r0],#1
64 subs r2, r2, #1
65 cmp r3, r1
66 beq 50f @ If it matches exit found
67 tst r0, #7
68 bne 5b @ If not aligned yet then do next byte
69
7010:
71 @ At this point, we are aligned, we know we have at least 8 bytes to work with
72 push {r4,r5,r6,r7}
73 cfi_adjust_cfa_offset (16)
74 cfi_rel_offset (r4, 0)
75 cfi_rel_offset (r5, 4)
76 cfi_rel_offset (r6, 8)
77 cfi_rel_offset (r7, 12)
78
79 cfi_remember_state
80
81 orr r1, r1, r1, lsl #8 @ expand the match word across to all bytes
82 orr r1, r1, r1, lsl #16
83 bic r6, r2, #7 @ Number of double words to work with * 8
84 mvns r7, #0 @ all F's
85 movs r3, #0
86
8715:
88 ldrd r4,r5, [r0],#8
89 subs r6, r6, #8
90 eor r4,r4, r1 @ Get it so that r4,r5 have 00's where the bytes match the target
91 eor r5,r5, r1
92 uadd8 r4, r4, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0
93 sel r4, r3, r7 @ bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
94 uadd8 r5, r5, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0
95 sel r5, r4, r7 @ chained....bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
96 cbnz r5, 60f
97 bne 15b @ (Flags from the subs above) If not run out of bytes then go around again
98
99 pop {r4,r5,r6,r7}
100 cfi_adjust_cfa_offset (-16)
101 cfi_restore (r4)
102 cfi_restore (r5)
103 cfi_restore (r6)
104 cfi_restore (r7)
105
106 and r1,r1,#0xff @ Get r1 back to a single character from the expansion above
107 and r2,r2,#7 @ Leave the count remaining as the number after the double words have been done
108
10920:
110 cbz r2, 40f @ 0 length or hit the end already then not found
111
11221: @ Post aligned section, or just a short call
113 ldrb r3,[r0],#1
114 subs r2,r2,#1
115 eor r3,r3,r1 @ r3 = 0 if match - doesn't break flags from sub
116 cbz r3, 50f
117 bne 21b @ on r2 flags
118
11940:
120 movs r0,#0 @ not found
121 DO_RET(lr)
122
12350:
124 subs r0,r0,#1 @ found
125 DO_RET(lr)
126
12760: @ We're here because the fast path found a hit - now we have to track down exactly which word it was
128 @ r0 points to the start of the double word after the one that was tested
129 @ r4 has the 00/ff pattern for the first word, r5 has the chained value
130 cfi_restore_state
131 cmp r4, #0
132 itte eq
133 moveq r4, r5 @ the end is in the 2nd word
134 subeq r0,r0,#3 @ Points to 2nd byte of 2nd word
135 subne r0,r0,#7 @ or 2nd byte of 1st word
136
137 @ r0 currently points to the 2nd byte of the word containing the hit
138 tst r4, # CHARTSTMASK(0) @ 1st character
139 bne 61f
140 adds r0,r0,#1
141 tst r4, # CHARTSTMASK(1) @ 2nd character
142 ittt eq
143 addeq r0,r0,#1
144 tsteq r4, # (3<<15) @ 2nd & 3rd character
145 @ If not the 3rd must be the last one
146 addeq r0,r0,#1
147
14861:
149 pop {r4,r5,r6,r7}
150 cfi_adjust_cfa_offset (-16)
151 cfi_restore (r4)
152 cfi_restore (r5)
153 cfi_restore (r6)
154 cfi_restore (r7)
155
156 subs r0,r0,#1
157 DO_RET(lr)
158
159END(memchr)
160libc_hidden_builtin_def (memchr)
161

source code of glibc/sysdeps/arm/armv6t2/memchr.S