forgejo/vendor/github.com/boombuler/barcode/utils/galoisfield.go
Andrew 6dd096b7f0 Two factor authentication support (#630)
* Initial commit for 2FA support

Signed-off-by: Andrew <write@imaginarycode.com>

* Add vendored files

* Add missing depends

* A few clean ups

* Added improvements, proper encryption

* Better encryption key

* Simplify "key" generation

* Make 2FA enrollment page more robust

* Fix typo

* Rename twofa/2FA to TwoFactor

* UNIQUE INDEX -> UNIQUE
2017-01-16 10:14:29 +08:00

65 lines
1.3 KiB
Go

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]]
}