blob: 68726fbfdef45e206fe171d31f9125a03b3de048 (
plain)
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
|
package utils
// GaloisField encapsulates galois field arithmetics
type GaloisField struct {
Size int
Base int
ALogTbl []int
LogTbl []int
}
// NewGaloisField creates a new galois field
func NewGaloisField(pp, fieldSize, b int) *GaloisField {
result := new(GaloisField)
result.Size = fieldSize
result.Base = b
result.ALogTbl = make([]int, fieldSize)
result.LogTbl = make([]int, fieldSize)
x := 1
for i := 0; i < fieldSize; i++ {
result.ALogTbl[i] = x
x = x * 2
if x >= fieldSize {
x = (x ^ pp) & (fieldSize - 1)
}
}
for i := 0; i < fieldSize; i++ {
result.LogTbl[result.ALogTbl[i]] = int(i)
}
return result
}
func (gf *GaloisField) Zero() *GFPoly {
return NewGFPoly(gf, []int{0})
}
// AddOrSub add or substract two numbers
func (gf *GaloisField) AddOrSub(a, b int) int {
return a ^ b
}
// Multiply multiplys two numbers
func (gf *GaloisField) Multiply(a, b int) int {
if a == 0 || b == 0 {
return 0
}
return gf.ALogTbl[(gf.LogTbl[a]+gf.LogTbl[b])%(gf.Size-1)]
}
// Divide divides two numbers
func (gf *GaloisField) Divide(a, b int) int {
if b == 0 {
panic("divide by zero")
} else if a == 0 {
return 0
}
return gf.ALogTbl[(gf.LogTbl[a]-gf.LogTbl[b])%(gf.Size-1)]
}
func (gf *GaloisField) Invers(num int) int {
return gf.ALogTbl[(gf.Size-1)-gf.LogTbl[num]]
}
|
