50 lines
852 B
Go
50 lines
852 B
Go
package utils
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type GaloisField struct {
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ALogTbl []int
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LogTbl []int
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}
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func NewGaloisField(pp int) *GaloisField {
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result := new(GaloisField)
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fldSize := 256
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result.ALogTbl = make([]int, fldSize)
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result.LogTbl = make([]int, fldSize)
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x := 1
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for i := 0; i < fldSize; i++ {
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result.ALogTbl[i] = x
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x = x * 2
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if x >= fldSize {
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x = (x ^ pp) & (fldSize - 1)
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}
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}
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for i := 0; i < fldSize; 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) AddOrSub(a, b int) int {
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return a ^ b
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}
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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])%255]
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}
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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])%255]
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}
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