73 lines
1.2 KiB
Go
73 lines
1.2 KiB
Go
package reedsolomon
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// ref to https://en.wikiversity.org/wiki/Reed%E2%80%93Solomon_codes_for_coders
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// ref to https://www.jianshu.com/p/8208aad537bb
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// gf.go Galois Fields
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var (
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gfLog = []byte{}
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gfExp = []byte{}
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)
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const prim = 0x011d
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// init calls all initial funcs
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func init() {
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initTables()
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}
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// init gfExp and gfLog array
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func initTables() {
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gfExp = make([]byte, 512)
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gfLog = make([]byte, 256)
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var (
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x uint16 = 1
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)
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for i := 0; i < 255; i++ {
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gfExp[i] = byte(x)
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gfLog[x] = byte(i)
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x <<= 1
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// x overflow 256
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if (x & 0x100) != 0 {
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x ^= prim
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}
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}
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for i := 255; i < 512; i++ {
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gfExp[i] = gfExp[i-255]
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}
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}
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// multpy
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func gfMul(x, y byte) byte {
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if x == 0 || y == 0 {
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return 0
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}
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// byte max: 256 but exp cap is 512
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return gfExp[uint(gfLog[x])+uint(gfLog[y])]
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}
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// divide
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// func gfDiv(x, y byte) byte {
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// if y == 0 {
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// panic("zero division error")
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// }
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// if x == 0 {
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// return 0
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// }
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// return gfExp[(uint(gfLog[x])+255-uint(gfLog[y]))%255]
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// }
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// // inverse
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// func gfInverse(x byte) byte {
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// return gfExp[255-uint(gfLog[x])]
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// }
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// // pow
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// func gfPow(x, power byte) byte {
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// return gfExp[(gfLog[x]*power)%255]
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// }
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