-
-
Notifications
You must be signed in to change notification settings - Fork 41
/
ltf.go
150 lines (145 loc) · 3.59 KB
/
ltf.go
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
140
141
142
143
144
145
146
147
148
149
150
// Copyright ©2017 The bíogo Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package ltf8 provides LTF-8 integer encoding.
//
// LTF-8 integer encoding is specified in the CRAM format specification
// section 2.3.
package ltf8
import "math/bits"
// Len returns the number of bytes required to encode v.
func Len(v int64) int {
u := uint64(v)
switch {
case u < 0x80:
return 1
case u < 0x4000:
return 2
case u < 0x200000:
return 3
case u < 0x10000000:
return 4
case u < 0x800000000:
return 5
case u < 0x40000000000:
return 6
case u < 0x2000000000000:
return 7
case u < 0x100000000000000:
return 8
default:
return 9
}
}
// Decode decodes the LTF-8 encoding in b and returns the int64 value, its
// width in bytes and whether the decoding was successful. If the encoding
// is invalid, the expected length of b and false are returned. If b has zero
// length, zero, zero and false are returned.
func Decode(b []byte) (v int64, n int, ok bool) {
if len(b) == 0 {
return 0, 0, false
}
n = bits.LeadingZeros8(^(b[0])) + 1
if len(b) < n {
return 0, n, false
}
switch n {
case 1:
v = int64(b[0])
case 2:
v = int64(b[1]) | int64(b[0]&0x3f)<<8
case 3:
v = int64(b[2]) | int64(b[1])<<8 | int64(b[0]&0x1f)<<16
case 4:
v = int64(b[3]) | int64(b[2])<<8 | int64(b[1])<<16 | int64(b[0]&0x0f)<<24
case 5:
v = int64(b[4]) | int64(b[3])<<8 | int64(b[2])<<16 | int64(b[1])<<24 | int64(b[0]&0x07)<<32
case 6:
v = int64(b[5]) | int64(b[4])<<8 | int64(b[3])<<16 | int64(b[2])<<24 | int64(b[1])<<32 | int64(b[0]&0x03)<<40
case 7:
v = int64(b[6]) | int64(b[5])<<8 | int64(b[4])<<16 | int64(b[3])<<24 | int64(b[2])<<32 | int64(b[1])<<40 | int64(b[0]&0x01)<<48
case 8:
v = int64(b[7]) | int64(b[6])<<8 | int64(b[5])<<16 | int64(b[4])<<24 | int64(b[3])<<32 | int64(b[2])<<40 | int64(b[1])<<48
case 9:
v = int64(b[8]) | int64(b[7])<<8 | int64(b[6])<<16 | int64(b[5])<<24 | int64(b[4])<<32 | int64(b[3])<<40 | int64(b[2])<<48 | int64(b[1])<<56
}
return v, n, true
}
// Encode encodes v as an LTF-8 into b, which must be large enough, and
// and returns the number of bytes written.
func Encode(b []byte, v int64) int {
u := uint64(v)
switch {
case u < 0x80:
b[0] = byte(u)
return 1
case u < 0x4000:
_ = b[1]
b[0] = byte(u>>8)&0x3f | 0x80
b[1] = byte(u)
return 2
case u < 0x200000:
_ = b[2]
b[0] = byte(u>>16)&0x1f | 0xc0
b[1] = byte(u >> 8)
b[2] = byte(u)
return 3
case u < 0x10000000:
_ = b[3]
b[0] = byte(u>>24)&0x0f | 0xe0
b[1] = byte(u >> 16)
b[2] = byte(u >> 8)
b[3] = byte(u)
return 4
case u < 0x800000000:
_ = b[4]
b[0] = byte(u>>32)&0x07 | 0xf0
b[1] = byte(u >> 24)
b[2] = byte(u >> 16)
b[3] = byte(u >> 8)
b[4] = byte(u)
return 5
case u < 0x40000000000:
_ = b[5]
b[0] = byte(u>>40)&0x03 | 0xf8
b[1] = byte(u >> 32)
b[2] = byte(u >> 24)
b[3] = byte(u >> 16)
b[4] = byte(u >> 8)
b[5] = byte(u)
return 6
case u < 0x2000000000000:
_ = b[6]
b[0] = byte(u>>48)&0x01 | 0xfc
b[1] = byte(u >> 40)
b[2] = byte(u >> 32)
b[3] = byte(u >> 24)
b[4] = byte(u >> 16)
b[5] = byte(u >> 8)
b[6] = byte(u)
return 7
case u < 0x100000000000000:
_ = b[7]
b[0] = 0xfe
b[1] = byte(u >> 48)
b[2] = byte(u >> 40)
b[3] = byte(u >> 32)
b[4] = byte(u >> 24)
b[5] = byte(u >> 16)
b[6] = byte(u >> 8)
b[7] = byte(u)
return 8
default:
_ = b[8]
b[0] = 0xff
b[1] = byte(u >> 56)
b[2] = byte(u >> 48)
b[3] = byte(u >> 40)
b[4] = byte(u >> 32)
b[5] = byte(u >> 24)
b[6] = byte(u >> 16)
b[7] = byte(u >> 8)
b[8] = byte(u)
return 9
}
}