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
|
//+build ignore
package main
import (
"fmt"
)
var logTable = [fieldSize]int16{
-1, 0, 1, 25, 2, 50, 26, 198,
3, 223, 51, 238, 27, 104, 199, 75,
4, 100, 224, 14, 52, 141, 239, 129,
28, 193, 105, 248, 200, 8, 76, 113,
5, 138, 101, 47, 225, 36, 15, 33,
53, 147, 142, 218, 240, 18, 130, 69,
29, 181, 194, 125, 106, 39, 249, 185,
201, 154, 9, 120, 77, 228, 114, 166,
6, 191, 139, 98, 102, 221, 48, 253,
226, 152, 37, 179, 16, 145, 34, 136,
54, 208, 148, 206, 143, 150, 219, 189,
241, 210, 19, 92, 131, 56, 70, 64,
30, 66, 182, 163, 195, 72, 126, 110,
107, 58, 40, 84, 250, 133, 186, 61,
202, 94, 155, 159, 10, 21, 121, 43,
78, 212, 229, 172, 115, 243, 167, 87,
7, 112, 192, 247, 140, 128, 99, 13,
103, 74, 222, 237, 49, 197, 254, 24,
227, 165, 153, 119, 38, 184, 180, 124,
17, 68, 146, 217, 35, 32, 137, 46,
55, 63, 209, 91, 149, 188, 207, 205,
144, 135, 151, 178, 220, 252, 190, 97,
242, 86, 211, 171, 20, 42, 93, 158,
132, 60, 57, 83, 71, 109, 65, 162,
31, 45, 67, 216, 183, 123, 164, 118,
196, 23, 73, 236, 127, 12, 111, 246,
108, 161, 59, 82, 41, 157, 85, 170,
251, 96, 134, 177, 187, 204, 62, 90,
203, 89, 95, 176, 156, 169, 160, 81,
11, 245, 22, 235, 122, 117, 44, 215,
79, 174, 213, 233, 230, 231, 173, 232,
116, 214, 244, 234, 168, 80, 88, 175,
}
const (
// The number of elements in the field.
fieldSize = 256
// The polynomial used to generate the logarithm table.
//
// There are a number of polynomials that work to generate
// a Galois field of 256 elements. The choice is arbitrary,
// and we just use the first one.
//
// The possibilities are: 29, 43, 45, 77, 95, 99, 101, 105,
//* 113, 135, 141, 169, 195, 207, 231, and 245.
generatingPolynomial = 29
)
func main() {
t := generateExpTable()
fmt.Printf("var expTable = %#v\n", t)
//t2 := generateMulTableSplit(t)
//fmt.Printf("var mulTable = %#v\n", t2)
low, high := generateMulTableHalf(t)
fmt.Printf("var mulTableLow = %#v\n", low)
fmt.Printf("var mulTableHigh = %#v\n", high)
}
/**
* Generates the inverse log table.
*/
func generateExpTable() []byte {
result := make([]byte, fieldSize*2-2)
for i := 1; i < fieldSize; i++ {
log := logTable[i]
result[log] = byte(i)
result[log+fieldSize-1] = byte(i)
}
return result
}
func generateMulTable(expTable []byte) []byte {
result := make([]byte, 256*256)
for v := range result {
a := byte(v & 0xff)
b := byte(v >> 8)
if a == 0 || b == 0 {
result[v] = 0
continue
}
logA := int(logTable[a])
logB := int(logTable[b])
result[v] = expTable[logA+logB]
}
return result
}
func generateMulTableSplit(expTable []byte) [256][256]byte {
var result [256][256]byte
for a := range result {
for b := range result[a] {
if a == 0 || b == 0 {
result[a][b] = 0
continue
}
logA := int(logTable[a])
logB := int(logTable[b])
result[a][b] = expTable[logA+logB]
}
}
return result
}
func generateMulTableHalf(expTable []byte) (low [256][16]byte, high [256][16]byte) {
for a := range low {
for b := range low {
result := 0
if !(a == 0 || b == 0) {
logA := int(logTable[a])
logB := int(logTable[b])
result = int(expTable[logA+logB])
}
if (b & 0xf) == b {
low[a][b] = byte(result)
}
if (b & 0xf0) == b {
high[a][b>>4] = byte(result)
}
}
}
return
}
|
