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GenericKuonBase24.cs
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GenericKuonBase24.cs
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using System.Runtime.CompilerServices;
namespace Gapotchenko.FX.Data.Encoding;
/// <summary>
/// Provides a generic implementation of Kuon Base24 encoding.
/// </summary>
[EditorBrowsable(EditorBrowsableState.Never)]
public abstract class GenericKuonBase24 : TextDataEncoding, IBase24
{
private protected GenericKuonBase24(TextDataEncodingAlphabet alphabet, char paddingChar)
{
if (alphabet == null)
throw new ArgumentNullException(nameof(alphabet));
ValidateAlphabet(alphabet);
Alphabet = alphabet;
PaddingChar = paddingChar;
}
/// <summary>
/// The encoding alphabet.
/// </summary>
protected TextDataEncodingAlphabet Alphabet { get; }
/// <summary>
/// Validates alphabet.
/// </summary>
/// <param name="alphabet">The alphabet.</param>
protected virtual void ValidateAlphabet(TextDataEncodingAlphabet alphabet)
{
if (alphabet is null)
throw new ArgumentNullException(nameof(alphabet));
if (alphabet.Size != Base)
{
throw new ArgumentException(
string.Format("The alphabet size for {0} encoding should be equal to {1}.", this, Base),
nameof(alphabet));
}
}
/// <inheritdoc/>
protected override DataEncodingOptions GetEffectiveOptions(DataEncodingOptions options)
{
if ((options & DataEncodingOptions.Padding) == 0)
{
// Produce unpadded strings unless padding is explicitly requested.
options |= DataEncodingOptions.NoPadding;
}
return base.GetEffectiveOptions(options);
}
#region Parameters
/// <summary>
/// The base of the encoding.
/// </summary>
protected const int Base = 24;
/// <summary>
/// Number of bits per encoded symbol.
/// </summary>
protected const float BitsPerSymbol = 4.584962500721156181453738943947816f; // = log2(Base) = log2(24)
/// <summary>
/// Number of symbols per encoded block.
/// </summary>
protected const int SymbolsPerEncodedBlock = 7;
/// <summary>
/// Number of bytes per decoded block.
/// </summary>
protected const int BytesPerDecodedBlock = 4;
/// <summary>
/// Base32 encoding efficiency.
/// The efficiency is the ratio between number of bits in the input and the number of bits in the encoded output.
/// </summary>
public new const float Efficiency = (float)BytesPerDecodedBlock / SymbolsPerEncodedBlock;
#endregion
/// <inheritdoc/>
public int Radix => Base;
/// <inheritdoc/>
protected override float EfficiencyCore => Efficiency;
const int LineWidth = SymbolsPerEncodedBlock * 11;
/// <summary>
/// Kuon Base24 encoding treats wrapping and indentation interchangeably.
/// </summary>
const DataEncodingOptions FormatMask = DataEncodingOptions.Wrap | DataEncodingOptions.Indent;
abstract class CodecContextBase
{
public CodecContextBase(TextDataEncodingAlphabet alphabet, char paddingChar, DataEncodingOptions options)
{
m_Alphabet = alphabet;
m_PaddingChar = paddingChar;
m_Options = options;
}
protected readonly TextDataEncodingAlphabet m_Alphabet;
protected readonly char m_PaddingChar;
protected readonly DataEncodingOptions m_Options;
#region Parameters
protected const string Name = "Kuon Base24";
#endregion
protected uint m_Bits;
protected int m_Modulus;
protected bool m_Eof;
}
sealed class EncoderContext : CodecContextBase, IEncoderContext
{
public EncoderContext(TextDataEncodingAlphabet alphabet, char paddingChar, DataEncodingOptions options) :
base(alphabet, paddingChar, options)
{
}
readonly char[] m_Buffer = new char[SymbolsPerEncodedBlock];
int m_LinePosition;
void MoveLinePosition(int delta) => m_LinePosition += delta;
void EmitLineBreak(TextWriter output)
{
if (m_LinePosition >= LineWidth)
{
m_LinePosition = 0;
if ((m_Options & FormatMask) != 0)
output.WriteLine();
}
}
void WriteBits(TextWriter output, int bitCount)
{
var alphabet = m_Alphabet;
int i = 0;
float writtenBitCount = 0;
uint a = m_Bits & (uint)((1 << bitCount) - 1);
while (i < SymbolsPerEncodedBlock)
{
var si = (int)(a % Base);
a /= Base;
m_Buffer[i++] = Capitalize(alphabet[si]);
writtenBitCount += BitsPerSymbol;
if (a == 0 && writtenBitCount >= bitCount)
{
// All bits of information are written.
// It is necessary to stop now in order to preserve the original message length upon decoding.
break;
}
}
Array.Reverse(m_Buffer, 0, i);
if ((m_Options & DataEncodingOptions.NoPadding) == 0)
{
var paddingChar = Capitalize(m_PaddingChar);
while (i < SymbolsPerEncodedBlock)
m_Buffer[i++] = paddingChar;
}
EmitLineBreak(output);
output.Write(m_Buffer, 0, i);
}
public void Encode(ReadOnlySpan<byte> input, TextWriter output)
{
if (m_Eof)
return;
if (input == null)
{
m_Eof = true;
switch (m_Modulus)
{
case 0:
// Nothing to do.
break;
case 1:
WriteBits(output, 1 * 8);
break;
case 2:
WriteBits(output, 2 * 8);
break;
case 3:
WriteBits(output, 3 * 8);
break;
default:
throw new InvalidOperationException();
}
return;
}
var alphabet = m_Alphabet;
foreach (var b in input)
{
// Accumulate data bits.
m_Bits = (m_Bits << 8) | b;
if (++m_Modulus == BytesPerDecodedBlock)
{
m_Modulus = 0;
uint a = m_Bits;
for (int i = SymbolsPerEncodedBlock - 1; i >= 0; --i)
{
var si = (int)(a % Base);
a /= Base;
m_Buffer[i] = Capitalize(alphabet[si]);
}
EmitLineBreak(output);
output.Write(m_Buffer);
MoveLinePosition(SymbolsPerEncodedBlock);
}
}
}
char Capitalize(char c) => TextDataEncoding.Capitalize(c, m_Options);
}
sealed class DecoderContext : CodecContextBase, IDecoderContext
{
public DecoderContext(TextDataEncodingAlphabet alphabet, char paddingChar, DataEncodingOptions options) :
base(alphabet, paddingChar, options)
{
}
readonly byte[] m_Buffer = new byte[BytesPerDecodedBlock];
public bool Decode(ReadOnlySpan<char> input, Stream output, bool throwOnError)
{
if (m_Eof)
return true;
var options = m_Options;
bool padding = (options & DataEncodingOptions.Padding) != 0;
if (input == null)
{
m_Eof = true;
if (padding)
{
if (!ValidatePaddingEof(throwOnError))
return false;
}
FlushDecode(output);
return true;
}
var alphabet = m_Alphabet;
bool isCaseSensitive = alphabet.IsCaseSensitive;
var paddingChar = m_PaddingChar;
bool relax = (options & DataEncodingOptions.Relax) != 0;
foreach (var c in input)
{
if (CharEqual(c, paddingChar, isCaseSensitive))
{
if (padding)
{
if (!ValidatePaddingChar(throwOnError))
return false;
}
FlushDecode(output);
continue;
}
int b = alphabet.IndexOf(c);
if (b == -1)
{
if (!relax)
{
if ((m_Options & DataEncodingOptions.Pure) != 0 ||
!char.IsWhiteSpace(c))
{
if (throwOnError)
throw new InvalidDataException($"Encountered an invalid {Name} character.");
return false;
}
}
continue;
}
if (!ValidatePaddingState(throwOnError))
return false;
// Accumulate data bits.
m_Bits = m_Bits * Base + (byte)b;
if (++m_Modulus == SymbolsPerEncodedBlock)
{
m_Modulus = 0;
m_Buffer[0] = (byte)(m_Bits >> 24);
m_Buffer[1] = (byte)(m_Bits >> 16);
m_Buffer[2] = (byte)(m_Bits >> 8);
m_Buffer[3] = (byte)m_Bits;
output.Write(m_Buffer, 0, BytesPerDecodedBlock);
m_Bits = 0;
}
}
return true;
}
void ReadBits(Stream output, float bitCount)
{
int i = 0; // output byte index
float s = bitCount; // shift accumulator
var a = m_Bits;
do
{
m_Buffer[i++] = (byte)a;
a >>= 8;
s -= 8;
}
while (s >= BitsPerSymbol);
Array.Reverse(m_Buffer, 0, i);
output.Write(m_Buffer, 0, i);
}
void FlushDecode(Stream output)
{
switch (m_Modulus)
{
case 0:
// Nothing to do.
return;
case var k when k > 0 && k < SymbolsPerEncodedBlock:
ReadBits(output, k * BitsPerSymbol);
break;
default:
throw new InvalidOperationException();
}
m_Modulus = 0;
}
int m_Padding;
bool ValidatePaddingChar(bool throwOnError)
{
if (m_Padding == 0)
{
if (m_Modulus == 0)
{
if (throwOnError)
throw CreateInvalidPaddingException();
return false;
}
m_Padding = m_Modulus;
}
if (++m_Padding == SymbolsPerEncodedBlock)
m_Padding = 0;
return true;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
bool ValidatePaddingState(bool throwOnError)
{
if (m_Padding != 0)
{
if (throwOnError)
throw CreateInvalidPaddingException();
return false;
}
return true;
}
bool ValidatePaddingEof(bool throwOnError)
{
if (m_Modulus != 0 || m_Padding != 0)
{
if (throwOnError)
throw CreateInvalidPaddingException();
return false;
}
return true;
}
static InvalidDataException CreateInvalidPaddingException() => new InvalidDataException($"Invalid {Name} padding.");
}
/// <inheritdoc/>
protected sealed override IEncoderContext CreateEncoderContext(DataEncodingOptions options) =>
CreateEncoderContextCore(Alphabet, options);
/// <inheritdoc/>
protected sealed override IDecoderContext CreateDecoderContext(DataEncodingOptions options) =>
CreateDecoderContextCore(Alphabet, options);
/// <summary>
/// Creates encoder context with specified alphabet and options.
/// </summary>
/// <param name="alphabet">The alphabet.</param>
/// <param name="options">The options.</param>
/// <returns>The encoder context.</returns>
protected virtual IEncoderContext CreateEncoderContextCore(TextDataEncodingAlphabet alphabet, DataEncodingOptions options) =>
new EncoderContext(alphabet, PaddingChar, options);
/// <summary>
/// Creates decoder context with specified alphabet and options.
/// </summary>
/// <param name="alphabet">The alphabet.</param>
/// <param name="options">The options.</param>
/// <returns>A decoder context instance.</returns>
protected virtual IDecoderContext CreateDecoderContextCore(TextDataEncodingAlphabet alphabet, DataEncodingOptions options) =>
new DecoderContext(alphabet, PaddingChar, options);
/// <inheritdoc/>
public sealed override bool IsCaseSensitive => Alphabet.IsCaseSensitive;
/// <inheritdoc/>
protected sealed override int PaddingCore => SymbolsPerEncodedBlock;
/// <summary>
/// The padding character.
/// </summary>
protected char PaddingChar { get; }
/// <inheritdoc/>
protected override string PadCore(ReadOnlySpan<char> s) => PadRight(s, PaddingChar);
/// <inheritdoc/>
protected override ReadOnlySpan<char> UnpadCore(ReadOnlySpan<char> s) => s.TrimEnd(PaddingChar);
/// <inheritdoc/>
public override bool CanCanonicalize => Alphabet.IsCanonicalizable;
/// <inheritdoc/>
protected override void CanonicalizeCore(ReadOnlySpan<char> source, Span<char> destination) => Alphabet.Canonicalize(source, destination);
/// <inheritdoc/>
protected override int GetMaxCharCountCore(int byteCount, DataEncodingOptions options)
{
int charCount = (byteCount * SymbolsPerEncodedBlock + BytesPerDecodedBlock - 1) / BytesPerDecodedBlock;
if ((options & DataEncodingOptions.NoPadding) == 0)
charCount = Pad(charCount);
int newLineCount =
(options & FormatMask) != 0 ?
Math.Max(charCount - 1, 0) / LineWidth :
0;
return charCount + newLineCount * MaxNewLineCharCount;
}
/// <inheritdoc/>
protected override int GetMaxByteCountCore(int charCount, DataEncodingOptions options) =>
(charCount * BytesPerDecodedBlock + SymbolsPerEncodedBlock - 1) / SymbolsPerEncodedBlock;
}