update

2022-12-13 22:47:31 +08:00
parent 9e7b10c1a5
commit df178687ba
40 changed files with 5401 additions and 15 deletions
@@ -0,0 +1,181 @@
+using System;
+using System.IO;
+using System.Text;
+
+namespace BaseNcoding
+{
+	public class Base85 : Base
+	{
+		public const string DefaultAlphabet = "!\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstu";
+		public const char DefaultSpecial = (char)0;
+		private static readonly uint[] Pow85 = { 85 * 85 * 85 * 85, 85 * 85 * 85, 85 * 85, 85, 1 };
+
+		public const string Prefix = "<~";
+		public const string Postfix = "~>";
+
+		public override bool HasSpecial => false;
+
+		public bool PrefixPostfix { get; set; }
+
+		public Base85(string alphabet = DefaultAlphabet, char special = DefaultSpecial, bool prefixPostfix = false, Encoding textEncoding = null)
+			: base(85, alphabet, special, textEncoding)
+		{
+			PrefixPostfix = prefixPostfix;
+			BlockBitsCount = 32;
+			BlockCharsCount = 5;
+		}
+
+		public override string Encode(byte[] data)
+		{
+			unchecked
+			{
+				byte[] encodedBlock = new byte[5];
+				int decodedBlockLength = 4;
+				int resultLength = data.Length * (encodedBlock.Length / decodedBlockLength);
+				if (PrefixPostfix)
+					resultLength += Prefix.Length + Postfix.Length;
+				char[] result = new char[resultLength];
+				int resultInd = 0;
+
+				if (PrefixPostfix)
+					CopyString(Prefix, result, ref resultInd);
+
+				int count = 0;
+				uint tuple = 0;
+				foreach (byte b in data)
+				{
+					if (count >= decodedBlockLength - 1)
+					{
+						tuple |= b;
+						if (tuple == 0)
+							result[resultInd++] = 'z';
+						else
+							EncodeBlock(encodedBlock.Length, result, ref resultInd, encodedBlock, tuple);
+						tuple = 0;
+						count = 0;
+					}
+					else
+					{
+						tuple |= (uint)(b << (24 - count * 8));
+						count++;
+					}
+				}
+
+				if (count > 0)
+					EncodeBlock(count + 1, result, ref resultInd, encodedBlock, tuple);
+
+				if (PrefixPostfix)
+					CopyString(Postfix, result, ref resultInd);
+
+				return new string(result);
+			}
+		}
+
+		public override byte[] Decode(string data)
+		{
+			unchecked
+			{
+				string dataWithoutPrefixPostfix = data;
+				if (PrefixPostfix)
+				{
+					if (!dataWithoutPrefixPostfix.StartsWith(Prefix) || !dataWithoutPrefixPostfix.EndsWith(Postfix))
+					{
+						throw new Exception("ASCII85 encoded data should begin with '" + Prefix + "' and end with '" + Postfix + "'");
+					}
+					dataWithoutPrefixPostfix = dataWithoutPrefixPostfix.Substring(Prefix.Length, dataWithoutPrefixPostfix.Length - Prefix.Length - Postfix.Length);
+				}
+
+				MemoryStream ms = new MemoryStream();
+				int count = 0;
+
+				uint tuple = 0;
+				int encodedBlockLength = 5;
+				byte[] decodedBlock = new byte[4];
+				foreach (char c in dataWithoutPrefixPostfix)
+				{
+					bool processChar;
+					switch (c)
+					{
+						case 'z':
+							if (count != 0)
+							{
+								throw new Exception("The character 'z' is invalid inside an ASCII85 block.");
+							}
+							decodedBlock[0] = 0;
+							decodedBlock[1] = 0;
+							decodedBlock[2] = 0;
+							decodedBlock[3] = 0;
+							ms.Write(decodedBlock, 0, decodedBlock.Length);
+							processChar = false;
+							break;
+						default:
+							processChar = true;
+							break;
+					}
+
+					if (processChar)
+					{
+						tuple += (uint)InvAlphabet[c] * Pow85[count];
+						count++;
+						if (count == encodedBlockLength)
+						{
+							DecodeBlock(decodedBlock.Length, decodedBlock, tuple);
+							ms.Write(decodedBlock, 0, decodedBlock.Length);
+							tuple = 0;
+							count = 0;
+						}
+					}
+				}
+
+				if (count != 0)
+				{
+					if (count == 1)
+					{
+						throw new Exception("The last block of ASCII85 data cannot be a single byte.");
+					}
+					count--;
+					tuple += Pow85[count];
+					DecodeBlock(count, decodedBlock, tuple);
+					for (int i = 0; i < count; i++)
+					{
+						ms.WriteByte(decodedBlock[i]);
+					}
+				}
+
+				return ms.ToArray();
+			}
+		}
+
+		private static void CopyString(string source, char[] dest, ref int destInd)
+		{
+			for (int i = 0; i < source.Length; i++)
+				dest[destInd++] = source[i];
+		}
+
+		private void EncodeBlock(int count, char[] result, ref int resultInd, byte[] encodedBlock, uint tuple)
+		{
+			unchecked
+			{
+				for (int i = encodedBlock.Length - 1; i >= 0; i--)
+				{
+					uint quotient = tuple % 85;
+					uint remainder = tuple - quotient * 85;
+					tuple = quotient;
+					encodedBlock[i] = (byte)remainder;
+				}
+
+				for (int i = 0; i < count; i++)
+					result[resultInd++] = Alphabet[encodedBlock[i]];
+			}
+		}
+
+		private void DecodeBlock(int bytes, byte[] decodedBlock, uint tuple)
+		{
+			unchecked
+			{
+				for (int i = 0; i < bytes; i++)
+					decodedBlock[i] = (byte)(tuple >> 24 - i * 8);
+			}
+		}
+	}
+}