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