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
133
134
135
136
137
138
139
|
//
// Copyright (c) 2014, ARM Limited
// All rights Reserved.
// SPDX-License-Identifier: BSD-2-Clause-Patent
//
// Assumptions:
//
// ARMv8-a, AArch64
// Neon Available.
//
// Arguments and results.
#define srcin x0
#define cntin x1
#define chrin w2
#define result x0
#define src x3
#define tmp x4
#define wtmp2 w5
#define synd x6
#define soff x9
#define cntrem x10
#define vrepchr v0
#define vdata1 v1
#define vdata2 v2
#define vhas_chr1 v3
#define vhas_chr2 v4
#define vrepmask v5
#define vend v6
//
// Core algorithm:
//
// For each 32-byte chunk we calculate a 64-bit syndrome value, with two bits
// per byte. For each tuple, bit 0 is set if the relevant byte matched the
// requested character and bit 1 is not used (faster than using a 32bit
// syndrome). Since the bits in the syndrome reflect exactly the order in which
// things occur in the original string, counting trailing zeros allows to
// identify exactly which byte has matched.
//
ASM_GLOBAL ASM_PFX(InternalMemScanMem8)
ASM_PFX(InternalMemScanMem8):
// Do not dereference srcin if no bytes to compare.
cbz cntin, .Lzero_length
//
// Magic constant 0x40100401 allows us to identify which lane matches
// the requested byte.
//
mov wtmp2, #0x0401
movk wtmp2, #0x4010, lsl #16
dup vrepchr.16b, chrin
// Work with aligned 32-byte chunks
bic src, srcin, #31
dup vrepmask.4s, wtmp2
ands soff, srcin, #31
and cntrem, cntin, #31
b.eq .Lloop
//
// Input string is not 32-byte aligned. We calculate the syndrome
// value for the aligned 32 bytes block containing the first bytes
// and mask the irrelevant part.
//
ld1 {vdata1.16b, vdata2.16b}, [src], #32
sub tmp, soff, #32
adds cntin, cntin, tmp
cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
and vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b
and vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b
addp vend.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128
addp vend.16b, vend.16b, vend.16b // 128->64
mov synd, vend.d[0]
// Clear the soff*2 lower bits
lsl tmp, soff, #1
lsr synd, synd, tmp
lsl synd, synd, tmp
// The first block can also be the last
b.ls .Lmasklast
// Have we found something already?
cbnz synd, .Ltail
.Lloop:
ld1 {vdata1.16b, vdata2.16b}, [src], #32
subs cntin, cntin, #32
cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
// If we're out of data we finish regardless of the result
b.ls .Lend
// Use a fast check for the termination condition
orr vend.16b, vhas_chr1.16b, vhas_chr2.16b
addp vend.2d, vend.2d, vend.2d
mov synd, vend.d[0]
// We're not out of data, loop if we haven't found the character
cbz synd, .Lloop
.Lend:
// Termination condition found, let's calculate the syndrome value
and vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b
and vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b
addp vend.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128
addp vend.16b, vend.16b, vend.16b // 128->64
mov synd, vend.d[0]
// Only do the clear for the last possible block
b.hi .Ltail
.Lmasklast:
// Clear the (32 - ((cntrem + soff) % 32)) * 2 upper bits
add tmp, cntrem, soff
and tmp, tmp, #31
sub tmp, tmp, #32
neg tmp, tmp, lsl #1
lsl synd, synd, tmp
lsr synd, synd, tmp
.Ltail:
// Count the trailing zeros using bit reversing
rbit synd, synd
// Compensate the last post-increment
sub src, src, #32
// Check that we have found a character
cmp synd, #0
// And count the leading zeros
clz synd, synd
// Compute the potential result
add result, src, synd, lsr #1
// Select result or NULL
csel result, xzr, result, eq
ret
.Lzero_length:
mov result, #0
ret
|
