128 lines
4.1 KiB
C#
128 lines
4.1 KiB
C#
using System;
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using System.IO;
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/*
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* Reference arithmetic coding
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* Copyright (c) Project Nayuki
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*
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* https://www.nayuki.io/page/reference-arithmetic-coding
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* https://github.com/nayuki/Reference-arithmetic-coding
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*/
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/// <summary>
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/// Compression application using static arithmetic coding.
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/// <para>Usage: java ArithmeticCompress InputFile OutputFile</para>
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/// <para>Then use the corresponding "ArithmeticDecompress" application to recreate the original input file.</para>
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/// <para>Note that the application uses an alphabet of 257 symbols - 256 symbols for the byte
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/// values and 1 symbol for the EOF marker. The compressed file format starts with a list
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/// of 256 symbol frequencies, and then followed by the arithmetic-coded data.</para>
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/// </summary>
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public class ArithmeticCompress
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{
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//JAVA TO C# CONVERTER WARNING: Method 'throws' clauses are not available in C#:
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//ORIGINAL LINE: public static void main(String[] args) throws java.io.IOException
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public static void Main(string[] args)
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{
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/* @@ PORT
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// Handle command line arguments
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if (args.Length != 2)
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{
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Console.Error.WriteLine("Usage: java ArithmeticCompress InputFile OutputFile");
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Environment.Exit(1);
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return;
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}
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File inputFile = new File(args[0]);
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File outputFile = new File(args[1]);
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// Read input file once to compute symbol frequencies
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FrequencyTable freqs = getFrequencies(inputFile);
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freqs.increment(256); // EOF symbol gets a frequency of 1
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// Read input file again, compress with arithmetic coding, and write output file
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using (Stream @in = new BufferedInputStream(new FileStream(inputFile, FileMode.Open, FileAccess.Read)), BitOutputStream @out = new BitOutputStream(new BufferedOutputStream(new FileStream(outputFile, FileMode.Create, FileAccess.Write))))
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{
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writeFrequencies(@out, freqs);
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compress(freqs, @in, @out);
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}
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*/
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}
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// Returns a frequency table based on the bytes in the given file.
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// Also contains an extra entry for symbol 256, whose frequency is set to 0.
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//JAVA TO C# CONVERTER WARNING: Method 'throws' clauses are not available in C#:
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//ORIGINAL LINE: private static FrequencyTable getFrequencies(java.io.File file) throws java.io.IOException
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private static FrequencyTable getFrequencies(string file)
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{
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FrequencyTable freqs = new SimpleFrequencyTable(new int[257]);
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using (Stream input = new BufferedStream( new FileStream(file, FileMode.Open, FileAccess.Read)))
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{
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while (true)
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{
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int b = input.ReadByte();
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if (b == -1)
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{
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break;
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}
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freqs.increment(b);
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}
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}
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return freqs;
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}
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// To allow unit testing, this method is package-private instead of private.
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//JAVA TO C# CONVERTER WARNING: Method 'throws' clauses are not available in C#:
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//ORIGINAL LINE: static void writeFrequencies(BitOutputStream out, FrequencyTable freqs) throws java.io.IOException
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internal static void writeFrequencies(BitOutputStream @out, FrequencyTable freqs)
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{
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for (int i = 0; i < 256; i++)
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{
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writeInt(@out, 32, freqs.get(i));
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}
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}
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// To allow unit testing, this method is package-private instead of private.
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//JAVA TO C# CONVERTER WARNING: Method 'throws' clauses are not available in C#:
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//ORIGINAL LINE: static void compress(FrequencyTable freqs, java.io.InputStream in, BitOutputStream out) throws java.io.IOException
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internal static void compress(FrequencyTable freqs, Stream @in, BitOutputStream @out)
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{
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ArithmeticEncoder enc = new ArithmeticEncoder(32, @out);
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while (true)
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{
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int symbol = @in.ReadByte();
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if (symbol == -1)
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{
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break;
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}
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enc.write(freqs, symbol);
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}
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enc.write(freqs, 256); // EOF
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enc.finish(); // Flush remaining code bits
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}
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// Writes an unsigned integer of the given bit width to the given stream.
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//JAVA TO C# CONVERTER WARNING: Method 'throws' clauses are not available in C#:
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//ORIGINAL LINE: private static void writeInt(BitOutputStream out, int numBits, int value) throws java.io.IOException
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private static void writeInt(BitOutputStream @out, int numBits, int value)
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{
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if (numBits < 0 || numBits > 32)
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{
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throw new System.ArgumentException();
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}
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for (int i = numBits - 1; i >= 0; i--)
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{
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@out.write(((int)((uint)value >> i)) & 1); // Big endian
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}
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}
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}
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