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133 lines
3.2 KiB
Go
133 lines
3.2 KiB
Go
//+build ignore
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package main
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import (
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"fmt"
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)
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var logTable = [fieldSize]int16{
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-1, 0, 1, 25, 2, 50, 26, 198,
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3, 223, 51, 238, 27, 104, 199, 75,
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4, 100, 224, 14, 52, 141, 239, 129,
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28, 193, 105, 248, 200, 8, 76, 113,
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5, 138, 101, 47, 225, 36, 15, 33,
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53, 147, 142, 218, 240, 18, 130, 69,
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29, 181, 194, 125, 106, 39, 249, 185,
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201, 154, 9, 120, 77, 228, 114, 166,
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6, 191, 139, 98, 102, 221, 48, 253,
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226, 152, 37, 179, 16, 145, 34, 136,
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54, 208, 148, 206, 143, 150, 219, 189,
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241, 210, 19, 92, 131, 56, 70, 64,
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30, 66, 182, 163, 195, 72, 126, 110,
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107, 58, 40, 84, 250, 133, 186, 61,
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202, 94, 155, 159, 10, 21, 121, 43,
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78, 212, 229, 172, 115, 243, 167, 87,
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7, 112, 192, 247, 140, 128, 99, 13,
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103, 74, 222, 237, 49, 197, 254, 24,
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227, 165, 153, 119, 38, 184, 180, 124,
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17, 68, 146, 217, 35, 32, 137, 46,
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55, 63, 209, 91, 149, 188, 207, 205,
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144, 135, 151, 178, 220, 252, 190, 97,
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242, 86, 211, 171, 20, 42, 93, 158,
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132, 60, 57, 83, 71, 109, 65, 162,
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31, 45, 67, 216, 183, 123, 164, 118,
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196, 23, 73, 236, 127, 12, 111, 246,
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108, 161, 59, 82, 41, 157, 85, 170,
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251, 96, 134, 177, 187, 204, 62, 90,
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203, 89, 95, 176, 156, 169, 160, 81,
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11, 245, 22, 235, 122, 117, 44, 215,
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79, 174, 213, 233, 230, 231, 173, 232,
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116, 214, 244, 234, 168, 80, 88, 175,
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}
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const (
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// The number of elements in the field.
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fieldSize = 256
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// The polynomial used to generate the logarithm table.
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//
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// There are a number of polynomials that work to generate
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// a Galois field of 256 elements. The choice is arbitrary,
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// and we just use the first one.
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//
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// The possibilities are: 29, 43, 45, 77, 95, 99, 101, 105,
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//* 113, 135, 141, 169, 195, 207, 231, and 245.
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generatingPolynomial = 29
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)
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func main() {
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t := generateExpTable()
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fmt.Printf("var expTable = %#v\n", t)
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//t2 := generateMulTableSplit(t)
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//fmt.Printf("var mulTable = %#v\n", t2)
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low, high := generateMulTableHalf(t)
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fmt.Printf("var mulTableLow = %#v\n", low)
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fmt.Printf("var mulTableHigh = %#v\n", high)
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}
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/**
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* Generates the inverse log table.
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*/
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func generateExpTable() []byte {
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result := make([]byte, fieldSize*2-2)
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for i := 1; i < fieldSize; i++ {
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log := logTable[i]
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result[log] = byte(i)
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result[log+fieldSize-1] = byte(i)
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}
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return result
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}
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func generateMulTable(expTable []byte) []byte {
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result := make([]byte, 256*256)
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for v := range result {
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a := byte(v & 0xff)
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b := byte(v >> 8)
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if a == 0 || b == 0 {
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result[v] = 0
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continue
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}
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logA := int(logTable[a])
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logB := int(logTable[b])
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result[v] = expTable[logA+logB]
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}
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return result
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}
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func generateMulTableSplit(expTable []byte) [256][256]byte {
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var result [256][256]byte
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for a := range result {
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for b := range result[a] {
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if a == 0 || b == 0 {
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result[a][b] = 0
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continue
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}
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logA := int(logTable[a])
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logB := int(logTable[b])
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result[a][b] = expTable[logA+logB]
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}
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}
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return result
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}
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func generateMulTableHalf(expTable []byte) (low [256][16]byte, high [256][16]byte) {
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for a := range low {
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for b := range low {
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result := 0
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if !(a == 0 || b == 0) {
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logA := int(logTable[a])
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logB := int(logTable[b])
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result = int(expTable[logA+logB])
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}
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if (b & 0xf) == b {
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low[a][b] = byte(result)
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}
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if (b & 0xf0) == b {
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high[a][b>>4] = byte(result)
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}
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}
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}
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return
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}
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