protected override (MetaBlock, BrotliGlobalState) Transform(MetaBlock.Compressed original, BrotliGlobalState state, BrotliCompressionParameters parameters)
{
var builder = new CompressedMetaBlockBuilder(original, state)
{
LiteralCtxMap = ContextMapBuilder.Literals.Simple,
DistanceCtxMap = ContextMapBuilder.Distances.Simple
};
foreach (var category in Categories.LID)
{
builder.BlockTypes[category].Reset();
}
builder.UseSameLiteralContextMode(LiteralContextMode.UTF8);
var tracker = new MetaBlockSizeTracker(state);
tracker.Test(builder, parameters);
foreach (var category in Categories.LID)
{
TestBlockSplits(builder, parameters, tracker, category);
}
tracker.Test(original);
return(tracker.Smallest ?? throw new InvalidOperationException("Transformation did not generate any meta-blocks."));
}
protected override (MetaBlock, BrotliGlobalState) Transform(MetaBlock.Compressed original, BrotliGlobalState state, BrotliCompressionParameters parameters)
{
var builder = new CompressedMetaBlockBuilder(original, state);
var tracker = new MetaBlockSizeTracker(state);
for (byte postfixBitCount = 0; postfixBitCount <= DistanceParameters.MaxPostfixBitCount; postfixBitCount++)
{
for (byte directCodeBits = 0; directCodeBits <= DistanceParameters.MaxDirectCodeBits; directCodeBits++)
{
builder.DistanceParameters = new DistanceParameters(postfixBitCount, directCodeBits);
tracker.Test(builder, parameters, debugText: "[PostfixBitCount = " + postfixBitCount + ", DirectCodeBits = " + directCodeBits + "]");
}
}
return(tracker.Smallest ?? throw new InvalidOperationException("Transformation did not generate any meta-blocks."));
}
protected override (MetaBlock, BrotliGlobalState) Transform(MetaBlock.Compressed original, BrotliGlobalState state, BrotliCompressionParameters parameters)
{
var builder = new CompressedMetaBlockBuilder(original, state);
var tracker = new MetaBlockSizeTracker(state);
tracker.Test(builder, parameters);
var blocker = new Blocker(parameters.DistanceCodePicker);
parameters = new BrotliCompressionParameters.Builder(parameters)
{
DistanceCodePicker = blocker.Pick
}.Build();
foreach (var code in DistanceCode.Last.Codes.Except(new DistanceCode[] { DistanceCode.Zero }))
{
var prev = tracker.SmallestSize;
blocker.BlockedCodes.Add(code);
tracker.Test(builder, parameters);
if (tracker.SmallestSize < prev)
{
Debug.WriteLine("Blocking code " + code + " reduced size (" + prev + " > " + tracker.SmallestSize + "), keeping it...");
}
else
{
Debug.WriteLine("Blocking code " + code + " did not improve the size, continuing...");
blocker.BlockedCodes.Remove(code);
}
}
Debug.WriteLine("Final blocked codes: " + string.Join(", ", blocker.BlockedCodes));
return(tracker.Smallest ?? throw new InvalidOperationException("Transformation did not generate any meta-blocks."));
}
private void TestBlockSplits(CompressedMetaBlockBuilder builder, BrotliCompressionParameters parameters, MetaBlockSizeTracker tracker, Category category)
{
int totalBlockLength = builder.GetTotalBlockLength(category);
if (totalBlockLength == 0)
{
return;
}
int step = Math.Max(1, (int)Math.Floor(Math.Log(totalBlockLength, 1.15)));
int stepTwice = step * 2;
if (totalBlockLength < stepTwice)
{
return;
}
var lengths = new List <int> {
totalBlockLength
};
var queue = new Queue <int>();
queue.Enqueue(0);
while (queue.TryDequeue(out int leftIndex))
{
if (lengths[leftIndex] < stepTwice)
{
continue;
}
int rightIndex = leftIndex + 1;
lengths.Insert(rightIndex, lengths[leftIndex] - step);
lengths[leftIndex] = step;
ApplyBlockSplit(builder.BlockTypes[category], lengths);
PrepareContextMap(builder, category, lengths.Count);
tracker.Test(builder, parameters);
while (lengths[leftIndex] + step < lengths[rightIndex] && lengths[rightIndex] >= stepTwice)
{
lengths[leftIndex] += step;
lengths[rightIndex] -= step;
ApplyBlockSplit(builder.BlockTypes[category], lengths);
PrepareContextMap(builder, category, lengths.Count);
tracker.Test(builder, parameters);
}
var smallest = tracker.Smallest;
if (smallest == null)
{
return;
}
var mb = smallest.Value.Item1;
int prev = lengths.Count;
lengths.Clear();
lengths.Add(mb.Header.BlockTypes[category].InitialLength);
lengths.AddRange(mb.Data.BlockSwitchCommands[category].Select(command => command.Length));
var finalLength = totalBlockLength - lengths.Sum();
if (finalLength > 0)
{
lengths.Add(totalBlockLength - lengths.Sum());
}
if (lengths.Count >= prev)
{
queue.Enqueue(leftIndex);
queue.Enqueue(rightIndex);
}
}
}
