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
|
/*
* memchr - scan memory for a character
*
* Copyright (c) 2010-2021, Arm Limited.
* SPDX-License-Identifier: MIT
*/
/*
Written by Dave Gilbert <david.gilbert@linaro.org>
This __memchr_arm routine is optimised on a Cortex-A9 and should work on
all ARMv7 processors. It has a fast past for short sizes, and has
an optimised path for large data sets; the worst case is finding the
match early in a large data set.
*/
@ 2011-02-07 david.gilbert@linaro.org
@ Extracted from local git a5b438d861
@ 2011-07-14 david.gilbert@linaro.org
@ Import endianness fix from local git ea786f1b
@ 2011-12-07 david.gilbert@linaro.org
@ Removed unneeded cbz from align loop
.syntax unified
.arch armv7-a
@ this lets us check a flag in a 00/ff byte easily in either endianness
#ifdef __ARMEB__
#define CHARTSTMASK(c) 1<<(31-(c*8))
#else
#define CHARTSTMASK(c) 1<<(c*8)
#endif
.thumb
@ ---------------------------------------------------------------------------
.thumb_func
.align 2
.p2align 4,,15
.global __memchr_arm
.type __memchr_arm,%function
__memchr_arm:
@ r0 = start of memory to scan
@ r1 = character to look for
@ r2 = length
@ returns r0 = pointer to character or NULL if not found
and r1,r1,#0xff @ Don't think we can trust the caller to actually pass a char
cmp r2,#16 @ If it's short don't bother with anything clever
blt 20f
tst r0, #7 @ If it's already aligned skip the next bit
beq 10f
@ Work up to an aligned point
5:
ldrb r3, [r0],#1
subs r2, r2, #1
cmp r3, r1
beq 50f @ If it matches exit found
tst r0, #7
bne 5b @ If not aligned yet then do next byte
10:
@ At this point, we are aligned, we know we have at least 8 bytes to work with
push {r4,r5,r6,r7}
orr r1, r1, r1, lsl #8 @ expand the match word across to all bytes
orr r1, r1, r1, lsl #16
bic r4, r2, #7 @ Number of double words to work with
mvns r7, #0 @ all F's
movs r3, #0
15:
ldmia r0!,{r5,r6}
subs r4, r4, #8
eor r5,r5, r1 @ Get it so that r5,r6 have 00's where the bytes match the target
eor r6,r6, r1
uadd8 r5, r5, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0
sel r5, r3, r7 @ bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
uadd8 r6, r6, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0
sel r6, r5, r7 @ chained....bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
cbnz r6, 60f
bne 15b @ (Flags from the subs above) If not run out of bytes then go around again
pop {r4,r5,r6,r7}
and r1,r1,#0xff @ Get r1 back to a single character from the expansion above
and r2,r2,#7 @ Leave the count remaining as the number after the double words have been done
20:
cbz r2, 40f @ 0 length or hit the end already then not found
21: @ Post aligned section, or just a short call
ldrb r3,[r0],#1
subs r2,r2,#1
eor r3,r3,r1 @ r3 = 0 if match - doesn't break flags from sub
cbz r3, 50f
bne 21b @ on r2 flags
40:
movs r0,#0 @ not found
bx lr
50:
subs r0,r0,#1 @ found
bx lr
60: @ We're here because the fast path found a hit - now we have to track down exactly which word it was
@ r0 points to the start of the double word after the one that was tested
@ r5 has the 00/ff pattern for the first word, r6 has the chained value
cmp r5, #0
itte eq
moveq r5, r6 @ the end is in the 2nd word
subeq r0,r0,#3 @ Points to 2nd byte of 2nd word
subne r0,r0,#7 @ or 2nd byte of 1st word
@ r0 currently points to the 3rd byte of the word containing the hit
tst r5, # CHARTSTMASK(0) @ 1st character
bne 61f
adds r0,r0,#1
tst r5, # CHARTSTMASK(1) @ 2nd character
ittt eq
addeq r0,r0,#1
tsteq r5, # (3<<15) @ 2nd & 3rd character
@ If not the 3rd must be the last one
addeq r0,r0,#1
61:
pop {r4,r5,r6,r7}
subs r0,r0,#1
bx lr
.size __memchr_arm, . - __memchr_arm
|
