103 lines
3.2 KiB
C#
103 lines
3.2 KiB
C#
using System.Buffers.Binary;
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using System.Text;
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namespace Phantom.Utils.Cryptography;
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// MIT License
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//
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// Copyright (c) 2020 Niklas Mollenhauer
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in all
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// copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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// SOFTWARE.
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//
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// ---------------------------------------------------------------------
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// This is a modified version of https://github.com/nikeee/dotnet-base24
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// ---------------------------------------------------------------------
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sealed class Base24 {
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private readonly string alphabet;
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private readonly uint alphabetLength;
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private readonly Dictionary<char, uint> decodeMap;
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public Base24(string alphabet) {
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this.alphabet = alphabet;
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this.alphabetLength = (uint) alphabet.Length;
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this.decodeMap = new Dictionary<char, uint>(alphabet.Length);
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for (int i = 0; i < alphabet.Length; ++i) {
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this.decodeMap[alphabet[i]] = (uint) i;
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}
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}
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public string Encode(ReadOnlySpan<byte> data) {
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if (data.Length == 0) {
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return string.Empty;
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}
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if (data.Length % 4 != 0) {
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throw new ArgumentException("The data length must be multiple of 4 bytes (32 bits).");
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}
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var encodedDataLength = (data.Length / 4) * 7;
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var result = new StringBuilder(encodedDataLength);
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Span<char> subResult = stackalloc char[7];
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for (int i = 0; i < data.Length; i += 4) {
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uint value = BinaryPrimitives.ReadUInt32LittleEndian(data[i..]);
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for (int k = 6; k >= 0; --k) {
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uint idx = value % alphabetLength;
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value /= alphabetLength;
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subResult[k] = alphabet[(int) idx];
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}
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result.Append(subResult);
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}
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return result.ToString();
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}
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public byte[] Decode(ReadOnlySpan<char> data) {
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if (data == null) {
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throw new ArgumentNullException(nameof(data));
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}
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if (data.Length % 7 != 0) {
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throw new ArgumentException("The data length must be multiple of 7 chars.");
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}
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var decodedDataLength = (data.Length / 7) * 4;
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var result = new byte[decodedDataLength];
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for (int i = 0; i < data.Length / 7; ++i) {
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var subData = data.Slice(i * 7, 7);
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uint value = 0;
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foreach (char c in subData) {
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value = (alphabetLength * value) + decodeMap[c];
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}
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var resultIndex = i * 4;
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BinaryPrimitives.WriteUInt32LittleEndian(result.AsSpan(resultIndex), value);
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}
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return result;
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}
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}
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