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package utils
// GaloisField encapsulates galois field arithmetics
type GaloisField struct {
ALogTbl []int
LogTbl []int
}
// NewGaloisField creates a new falois field
func NewGaloisField(pp int) *GaloisField {
result := new(GaloisField)
fldSize := 256
result.ALogTbl = make([]int, fldSize)
result.LogTbl = make([]int, fldSize)
x := 1
for i := 0; i < fldSize; i++ {
result.ALogTbl[i] = x
x = x * 2
if x >= fldSize {
x = (x ^ pp) & (fldSize - 1)
}
}
for i := 0; i < fldSize; i++ {
result.LogTbl[result.ALogTbl[i]] = int(i)
}
return result
}
// 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])%255]
}
// 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])%255]
}
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