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add support for ascii 85 decoding
This commit is contained in:
Eliot Jones
79
src/UglyToad.Pdf.Tests/Filters/Ascii85FilterTests.cs
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79
src/UglyToad.Pdf.Tests/Filters/Ascii85FilterTests.cs
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@@ -0,0 +1,79 @@
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namespace UglyToad.Pdf.Tests.Filters
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{
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using System.Text;
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using ContentStream;
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using Pdf.Filters;
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using Xunit;
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public class Ascii85FilterTests
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{
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private readonly Ascii85Filter filter = new Ascii85Filter();
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[Fact]
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public void DecodesWikipediaExample()
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{
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var bytes = Encoding.ASCII.GetBytes(
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@"9jqo^BlbD-BleB1DJ+*+F(f,q/0JhKF<GL>Cj@.4Gp$d7F!,L7@<6@)/0JDEF<G%<+EV:2F!,
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O<DJ+*.@<*K0@<6L(Df-\0Ec5e;DffZ(EZee.Bl.9pF""AGXBPCsi + DGm >@3BB / F * &OCAfu2 / AKY
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i(DIb: @FD, *) + C]U =@3BN#EcYf8ATD3s@q?d$AftVqCh[NqF<G:8+EV:.+Cf>-FD5W8ARlolDIa
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l(DId<j@<? 3r@:F % a + D58'ATD4$Bl@l3De:,-DJs`8ARoFb/0JMK@qB4^F!,R<AKZ&-DfTqBG%G
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> uD.RTpAKYo'+CT/5+Cei#DII?(E,9)oF*2M7/c~>");
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var result = filter.Decode(bytes, new PdfDictionary(), 0);
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var text = Encoding.ASCII.GetString(result);
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Assert.Equal("Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, " +
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"that by a perseverance of delight in the continued and indefatigable generation of knowledge, " +
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"exceeds the short vehemence of any carnal pleasure.",
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text);
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}
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[Fact]
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public void DecodesEncodedPdfContent()
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{
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const string input =
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@"0d&.mDdmGg4?O`>9P&*SFD)dS2E2gC4pl@QEb/Zr$8N_r$:7]!01IZ=0eskNAdU47<+?7h+B3Ol2_m!C+?)#1+B1
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`9>:<KhASu!rA7]9oF*)G6@;U'.@ps6t@V$[&ART*lARTXoCj@HP2DlU*/0HBI+B1r?0H_r%1a#ac$<nof.3LB""+=MAS+D58'ATD3qCj@.
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F@;@;70ea^uAKYi.Eb-A7E+*6f+EV:*DBN1?0ek+_+B1r?<%9""=ASu!rA7]9oF*)G6@;U'<.3MT)$8<SS1,pCU6jd-H;e7
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C#1,U1&Ft""Og2'=;YEa`c,ASu!rA8,po+Dk\3BQ%F&+CT;%+CQ]A1,'h!Ft""Oh2'=;UBl%3eCh4`'DBMbD7O]H>0H_br.:""&q8d[6p/M
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T()<(%'A;f?Ma+CT;%+E_a:A0>K&EZek1D/aN,F)u&6DBNA*A0>f4BOu4*+EM76E,9eK+B3(_<%9""p.!0AMEb031ATMF#F<G%,DIIR2+Cno
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&@3B9%+CT.1.3LK*+=KNS6V0ilAoD^,@<=+N>p**=$</Jt-rY&$AKYo'+EV:.+Cf>,E,oN2F(oQ1+D#G#De*R""B-;&&FD,T'F!+n3AKY4b
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F*22=@:F%a+=SF4C'moi+=Li?EZeh0FD)e-@<>p#@;]TuBl.9kATKCFGA(],AKYo5BOu4*+CT;%+C#7pF_Pr+@VfTuDf0B:+=SF4C'moi+=
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Li?EZek1DKKT1F`2DD/TboKAKY](@:s.m/h%oBC'mC/$>""*cF*)G6@;Q?_DIdZpC&~>";
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var result = filter.Decode(Encoding.ASCII.GetBytes(input), new PdfDictionary(), 0);
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var text = Encoding.ASCII.GetString(result);
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const string expected = @"1 0 obj
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<< /Length 568 >>
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stream
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2 J
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BT
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/F1 12 Tf
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0 Tc
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0 Tw
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72.5 712 TD
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[(Unencoded streams can be read easily) 65 (, )] TJ
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0 -14 TD
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[(b) 20 (ut generally tak) 10 (e more space than \311)] TJ
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T* (encoded streams.) Tj
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0 -28 TD
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[(Se) 25 (v) 15 (eral encoding methods are a) 20 (v) 25 (ailable in PDF) 80 (.)] TJ
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0 -14 TD
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(Some are used for compression and others simply) Tj
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T* [(to represent binary data in an ) 55 (ASCII format.)] TJ
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T* (Some of the compression encoding methods are \
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suitable ) Tj
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T* (for both data and images, while others are \
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suitable only ) Tj
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T* (for continuous-tone images.) Tj
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ET
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endstream
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endobj";
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Assert.Equal(expected.Replace("\r\n", "\n"), text);
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}
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}
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}
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145
src/UglyToad.Pdf/Filters/Ascii85Filter.cs
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145
src/UglyToad.Pdf/Filters/Ascii85Filter.cs
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@@ -0,0 +1,145 @@
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namespace UglyToad.Pdf.Filters
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{
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using System;
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using System.IO;
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using ContentStream;
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/// <summary>
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/// ASCII 85 (Base85) is a binary to text encoding using 5 ASCII characters per 4 bytes of data.
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/// </summary>
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public class Ascii85Filter : IFilter
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{
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private const byte EmptyBlock = (byte)'z';
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private const byte Offset = (byte)'!';
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private const byte EmptyCharacterPadding = (byte) 'u';
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private static readonly byte[] EndOfDataBytes = { (byte)'~', (byte)'>' };
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private static readonly int[] PowerByIndex = {
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1,
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85,
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85 * 85,
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85 * 85 * 85,
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85 * 85 * 85 *85
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};
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public byte[] Decode(byte[] input, PdfDictionary streamDictionary, int filterIndex)
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{
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var asciiBuffer = new byte[5];
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var index = 0;
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using (var stream = new MemoryStream())
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using (var writer = new BinaryWriter(stream))
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{
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for (var i = 0; i < input.Length; i++)
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{
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var value = input[i];
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if (IsWhiteSpace(value))
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{
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continue;
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}
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if (value == EndOfDataBytes[0])
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{
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if (i == input.Length - 1 || input[i + 1] == EndOfDataBytes[1])
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{
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if (index > 0)
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{
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WriteData(asciiBuffer, index, writer);
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}
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// The end
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break;
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}
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// TODO: this shouldn't be possible?
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}
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if (value == EmptyBlock)
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{
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if (index > 0)
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{
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// Should I throw here?
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}
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for (int j = 0; j < 4; j++)
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{
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writer.Write(0);
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}
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index = 0;
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// We've completed our block.
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}
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else
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{
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asciiBuffer[index] = (byte) (value - Offset);
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index++;
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}
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if (index == 5)
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{
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WriteData(asciiBuffer, index, writer);
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index = 0;
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}
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}
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writer.Flush();
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return stream.ToArray();
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}
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}
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private static void WriteData(byte[] ascii, int index, BinaryWriter writer)
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{
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if (index < 2)
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{
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throw new ArgumentOutOfRangeException(nameof(index), "Cannot convert a block padded by 4 'u' characters.");
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}
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// Write any empty padding if the block ended early.
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for (var i = index; i < 5; i++)
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{
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ascii[i] = EmptyCharacterPadding - Offset;
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}
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int value = 0;
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value += ascii[0] * PowerByIndex[4];
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value += ascii[1] * PowerByIndex[3];
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value += ascii[2] * PowerByIndex[2];
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value += ascii[3] * PowerByIndex[1];
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value += ascii[4] * PowerByIndex[0];
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writer.Write((byte)(value >> 24));
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if (index > 2)
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{
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writer.Write((byte) (value >> 16));
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}
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if (index > 3)
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{
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writer.Write((byte) (value >> 8));
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}
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if (index > 4)
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{
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writer.Write((byte) value);
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}
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}
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private static bool IsWhiteSpace(byte b)
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{
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if (b == '\r' || b == '\n' || b == ' ')
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{
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return true;
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}
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return false;
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}
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}
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}
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@@ -21,11 +21,14 @@
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public MemoryFilterProvider(IDecodeParameterResolver decodeParameterResolver, IPngPredictor pngPredictor, ILog log)
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{
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IFilter FlateFunc() => new FlateFilter(decodeParameterResolver, pngPredictor, log);
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IFilter Ascii85Func() => new Ascii85Filter();
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filterFactories = new Dictionary<CosName, Func<IFilter>>
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{
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{CosName.FLATE_DECODE, FlateFunc},
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{CosName.FLATE_DECODE_ABBREVIATION, FlateFunc},
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{CosName.ASCII85_DECODE, Ascii85Func},
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{CosName.ASCII85_DECODE_ABBREVIATION, Ascii85Func}
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};
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}
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