base58編碼與解碼實現

Base58編碼是比特幣地址生成算法中的最後一個步驟。算法簡單，和上大學時候學過的十進制轉十六進制一樣，只不過現在變成了十進制轉58進制，核心過程就是不斷的除58求餘。下面是Go語言的實現過程：

func Base58Encode(data []byte) string {
	var (
		alphabet = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
		bigNum = new(big.Int).SetBytes(data)
		divisor = big.NewInt(58)
		modulus = big.NewInt(0)
		result string
	)
	for {
		if bigNum.Cmp(big.NewInt(0)) == 0 {
			break
		}
		bigNum.DivMod(bigNum, divisor, modulus)
		result = string(alphabet[modulus.Int64()])+result
	}
	return result
}

func Base58Decode(data string) ([]byte,error) {
	var alphabetMap = map[string]int64 {
		"1":0,
		"2":1,
		"3":2,
		"4":3,
		"5":4,
		"6":5,
		"7":6,
		"8":7,
		"9":8,
		"A":9,
		"B":10,
		"C":11,
		"D":12,
		"E":13,
		"F":14,
		"G":15,
		"H":16,
		"J":17,
		"K":18,
		"L":19,
		"M":20,
		"N":21,
		"P":22,
		"Q":23,
		"R":24,
		"S":25,
		"T":26,
		"U":27,
		"V":28,
		"W":29,
		"X":30,
		"Y":31,
		"Z":32,
		"a":33,
		"b":34,
		"c":35,
		"d":36,
		"e":37,
		"f":38,
		"g":39,
		"h":40,
		"i":41,
		"j":42,
		"k":43,
		"m":44,
		"n":45,
		"o":46,
		"p":47,
		"q":48,
		"r":49,
		"s":50,
		"t":51,
		"u":52,
		"v":53,
		"w":54,
		"x":55,
		"y":56,
		"z":57,
	}
	var (
		bigNum = big.NewInt(0)
	)
	for _, d := range data {
		e,ok := alphabetMap[string(d)]
		if !ok {
			return nil,errors.New("contain invalid aplha")
		}
		//把58進制轉換成十進制
		bigNum.Mul(bigNum, big.NewInt(58))
		bigNum.Add(bigNum, new(big.Int).SetInt64(e))
	}

	return bigNum.Bytes(),nil
}

（全文完）