70 lines
2.3 KiB
C#
70 lines
2.3 KiB
C#
namespace System.IO.Compression
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{
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using System.Diagnostics;
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internal class CopyEncoder {
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// padding for copy encoder formatting
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// - 1 byte for header
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// - 4 bytes for len, nlen
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private const int PaddingSize = 5;
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// max uncompressed deflate block size is 64K.
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private const int MaxUncompressedBlockSize = 65536;
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// null input means write an empty payload with formatting info. This is needed for the final block.
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public void GetBlock(DeflateInput input, OutputBuffer output, bool isFinal) {
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Debug.Assert(output != null);
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Debug.Assert(output.FreeBytes >= PaddingSize);
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// determine number of bytes to write
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int count = 0;
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if (input != null) {
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// allow space for padding and bits not yet flushed to buffer
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count = Math.Min(input.Count, output.FreeBytes - PaddingSize - output.BitsInBuffer);
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// we don't expect the output buffer to ever be this big (currently 4K), but we'll check this
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// just in case that changes.
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if (count > MaxUncompressedBlockSize - PaddingSize) {
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count = MaxUncompressedBlockSize - PaddingSize;
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}
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}
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// write header and flush bits
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if (isFinal) {
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output.WriteBits(FastEncoderStatics.BFinalNoCompressionHeaderBitCount,
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FastEncoderStatics.BFinalNoCompressionHeader);
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}
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else {
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output.WriteBits(FastEncoderStatics.NoCompressionHeaderBitCount,
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FastEncoderStatics.NoCompressionHeader);
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}
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// now we're aligned
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output.FlushBits();
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// write len, nlen
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WriteLenNLen((ushort)count, output);
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// write uncompressed bytes
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if (input != null && count > 0) {
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output.WriteBytes(input.Buffer, input.StartIndex, count);
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input.ConsumeBytes(count);
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}
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}
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private void WriteLenNLen(ushort len, OutputBuffer output) {
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// len
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output.WriteUInt16(len);
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// nlen
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ushort onesComp = (ushort)(~(ushort)len);
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output.WriteUInt16(onesComp);
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}
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}
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}
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