63 lines
2.6 KiB
C#
63 lines
2.6 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Diagnostics;
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using System.Linq;
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using BrotliLib.Brotli;
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using BrotliLib.Brotli.Components;
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using BrotliLib.Brotli.Components.Data;
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using BrotliLib.Brotli.Encode;
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using BrotliLib.Brotli.Encode.Build;
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using BrotliLib.Brotli.Parameters;
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using BrotliLib.Brotli.Parameters.Heuristics;
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using BrotliLib.Collections;
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namespace BrotliImpl.Transformers{
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public class TransformAvoidLastDistanceCodes : BrotliTransformerCompressed{
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protected override (MetaBlock, BrotliGlobalState) Transform(MetaBlock.Compressed original, BrotliGlobalState state, BrotliCompressionParameters parameters){
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var builder = new CompressedMetaBlockBuilder(original, state);
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var tracker = new MetaBlockSizeTracker(state);
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tracker.Test(builder, parameters);
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var blocker = new Blocker(parameters.DistanceCodePicker);
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parameters = new BrotliCompressionParameters.Builder(parameters){
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DistanceCodePicker = blocker.Pick
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}.Build();
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foreach(var code in DistanceCode.Last.Codes.Except(new DistanceCode[]{ DistanceCode.Zero })){
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var prev = tracker.SmallestSize;
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blocker.BlockedCodes.Add(code);
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tracker.Test(builder, parameters);
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if (tracker.SmallestSize < prev){
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Debug.WriteLine("Blocking code " + code + " reduced size (" + prev + " > " + tracker.SmallestSize + "), keeping it...");
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}
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else{
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Debug.WriteLine("Blocking code " + code + " did not improve the size, continuing...");
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blocker.BlockedCodes.Remove(code);
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}
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}
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Debug.WriteLine("Final blocked codes: " + string.Join(", ", blocker.BlockedCodes));
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return tracker.Smallest ?? throw new InvalidOperationException("Transformation did not generate any meta-blocks.");
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}
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private class Blocker{
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public HashSet<DistanceCode> BlockedCodes { get; } = new HashSet<DistanceCode>();
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private readonly PickCodeHeuristics<DistanceCode>.Picker originalPicker;
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public Blocker(PickCodeHeuristics<DistanceCode>.Picker originalPicker){
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this.originalPicker = originalPicker;
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}
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public DistanceCode Pick(List<DistanceCode> picks, FrequencyList<DistanceCode> previouslySeen){
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picks.RemoveAll(BlockedCodes.Contains);
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return originalPicker(picks, previouslySeen);
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}
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}
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}
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}
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