122 lines
3.9 KiB
C#
122 lines
3.9 KiB
C#
using System;
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using System.Diagnostics;
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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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/// Decompression application using prediction by partial matching (PPM) with arithmetic coding.
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/// <para>Usage: java PpmDecompress InputFile OutputFile</para>
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/// <para>This decompresses files generated by the "PpmCompress" application.</para>
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/// </summary>
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public sealed class PpmDecompress
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{
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// Must be at least -1 and match PpmCompress. Warning: Exponential memory usage at O(257^n).
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private const int MODEL_ORDER = 3;
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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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// 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 PpmDecompress InputFile OutputFile");
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Environment.Exit(1);
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return;
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}
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string inputFile = args[0]; //new File(args[0]);
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string outputFile =args[1]; //new File(args[1]);
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// Perform file decompression
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using( BitInputStream @in = new BitInputStream(new BufferedStream(new FileStream(inputFile, FileMode.Open, FileAccess.Read))))
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using( Stream @out = new BufferedStream( new FileStream(outputFile, FileMode.Create, FileAccess.Write)))
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{
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decompress(@in, @out);
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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 decompress(BitInputStream in, java.io.OutputStream out) throws java.io.IOException
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internal static void decompress(BitInputStream @in, Stream @out)
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{
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// Set up decoder and model. In this PPM model, symbol 256 represents EOF;
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// its frequency is 1 in the order -1 context but its frequency
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// is 0 in all other contexts (which have non-negative order).
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ArithmeticDecoder dec = new ArithmeticDecoder(32, @in);
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PpmModel model = new PpmModel(MODEL_ORDER, 257, 256);
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int[] history = new int[0];
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while (true)
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{
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// Decode and write one byte
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int symbol = decodeSymbol(dec, model, history);
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if (symbol == 256) // EOF symbol
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{
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break;
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}
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@out.WriteByte((byte)symbol);
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model.incrementContexts(history, symbol);
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if (model.modelOrder >= 1)
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{
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// Prepend current symbol, dropping oldest symbol if necessary
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if (history.Length < model.modelOrder)
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{
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history = Arrays.CopyOf(history, history.Length + 1);
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}
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Array.Copy(history, 0, history, 1, history.Length - 1);
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history[0] = symbol;
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}
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}
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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: private static int decodeSymbol(ArithmeticDecoder dec, PpmModel model, int[] history) throws java.io.IOException
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private static int decodeSymbol(ArithmeticDecoder dec, PpmModel model, int[] history)
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{
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// Try to use highest order context that exists based on the history suffix. When symbol 256
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// is consumed at a context at any non-negative order, it means "escape to the next lower order
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// with non-empty context". When symbol 256 is consumed at the order -1 context, it means "EOF".
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for (int order = history.Length; order >= 0; order--)
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{
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PpmModel.Context ctx = model.rootContext;
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for (int i = 0; i < order; i++)
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{
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Debug.Assert(ctx.subcontexts == null);
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ctx = ctx.subcontexts[history[i]];
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if (ctx == null)
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{
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goto outerContinue;
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}
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}
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int symbol = dec.read(ctx.frequencies);
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if (symbol < 256)
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{
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return symbol;
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}
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// Else we read the context escape symbol, so continue decrementing the order
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outerContinue:;
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}
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outerBreak:
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// Logic for order = -1
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return dec.read(model.orderMinus1Freqs);
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}
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}
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