Two more differences between the LZW in HDGF and HMEF:
* Little Endian vs Big Endian storage of the code position * Initial dictionary position is the end of pre-fill, if there is one, rather than always being position 0 git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1078300 13f79535-47bb-0310-9956-ffa450edef68
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@ -41,23 +41,36 @@ public abstract class LZWDecompresser {
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* to get the real code length? Normally 2 or 3
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*/
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private final int codeLengthIncrease;
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/**
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* Does the 12 bits of the position get stored in
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* Little Endian or Big Endian form?
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* This controls whether a pos+length of 0x12 0x34
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* becomes a position of 0x123 or 0x312
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*/
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private final boolean positionIsBigEndian;
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protected LZWDecompresser(boolean maskMeansCompressed, int codeLengthIncrease) {
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protected LZWDecompresser(boolean maskMeansCompressed,
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int codeLengthIncrease, boolean positionIsBigEndian) {
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this.maskMeansCompressed = maskMeansCompressed;
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this.codeLengthIncrease = codeLengthIncrease;
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this.positionIsBigEndian = positionIsBigEndian;
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}
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/**
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* Populates the dictionary. May not need
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* to do anything if all zeros is fine.
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* Populates the dictionary, and returns where in it
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* to begin writing new codes.
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* Generally, if the dictionary is pre-populated, then new
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* codes should be placed at the end of that block.
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* Equally, if the dictionary is left with all zeros, then
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* usually the new codes can go in at the start.
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*/
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protected abstract void populateDictionary(byte[] dict);
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protected abstract int populateDictionary(byte[] dict);
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/**
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* Adjusts the position offset if needed when looking
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* something up in the dictionary.
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*/
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protected abstract int adjustDictionaryOffset(int offset);
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protected abstract int adjustDictionaryOffset(int offset);
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/**
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* Decompresses the given input stream, returning the array of bytes
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@ -83,17 +96,10 @@ public abstract class LZWDecompresser {
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* flag byte
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*/
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public void decompress(InputStream src, OutputStream res) throws IOException {
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// We use 12 bit codes:
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// * 0-255 are real bytes
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// * 256-4095 are the substring codes
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// Java handily initialises our buffer / dictionary
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// to all zeros
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byte[] buffer = new byte[4096];
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populateDictionary(buffer);
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// How far through the output we've got
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// (This is normally used &4095, so it nicely wraps)
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int pos = 0;
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// The initial value is set when populating the dictionary
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int pos;
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// The flag byte is treated as its 8 individual
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// bits, which tell us if the following 8 codes
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// are compressed or un-compressed
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@ -102,10 +108,18 @@ public abstract class LZWDecompresser {
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// processing each bit of the flag byte in turn
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int mask;
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// We use 12 bit codes:
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// * 0-255 are real bytes
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// * 256-4095 are the substring codes
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// Java handily initialises our buffer / dictionary
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// to all zeros
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byte[] buffer = new byte[4096];
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pos = populateDictionary(buffer);
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// These are bytes as looked up in the dictionary
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// It needs to be signed, as it'll get passed on to
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// the output stream
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byte[] dataB = new byte[19];
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byte[] dataB = new byte[16+codeLengthIncrease];
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// This is an unsigned byte read from the stream
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// It needs to be unsigned, so that bit stuff works
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int dataI;
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@ -121,7 +135,7 @@ public abstract class LZWDecompresser {
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// Is this a new code (un-compressed), or
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// the use of existing codes (compressed)?
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boolean isMaskSet = (flag & mask) > 0;
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if( isMaskSet && !maskMeansCompressed ) {
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if( isMaskSet ^ maskMeansCompressed ) {
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// Retrieve the un-compressed code
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if( (dataI = src.read()) != -1) {
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// Save the byte into the dictionary
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@ -139,11 +153,15 @@ public abstract class LZWDecompresser {
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// Build up how long the code sequence is, and
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// what position of the code to start at
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// (The position is the first 12 bits, the
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// length is the last 4 bits)
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// (The position is the usually the first 12 bits,
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// and the length is usually the last 4 bits)
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len = (dataIPt2 & 15) + codeLengthIncrease;
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pntr = (dataIPt2 & 240)*16 + dataIPt1;
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if(positionIsBigEndian) {
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pntr = (dataIPt1<<4) + (dataIPt2>>4);
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} else {
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pntr = dataIPt1 + ((dataIPt2&0xF0)<<4);
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}
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// Adjust the pointer as needed
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pntr = adjustDictionaryOffset(pntr);
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@ -37,8 +37,10 @@ import org.apache.poi.util.LZWDecompresser;
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*/
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public class HDGFLZW extends LZWDecompresser {
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public HDGFLZW() {
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// We're the wrong way round!
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super(false, 3);
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// Out flag is the wrong way round!
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// Length wise, we're 3 longer than we say, so the max len is 19
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// Endian wise, we're little endian, so 0x1234 is pos 0x312
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super(false, 3, false);
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}
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/**
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@ -63,12 +65,13 @@ public class HDGFLZW extends LZWDecompresser {
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}
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return pntr;
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}
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/**
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* We want an empty dictionary, so do nothing
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*/
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@Override
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protected void populateDictionary(byte[] dict) {
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protected int populateDictionary(byte[] dict) {
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return 0;
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}
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/**
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@ -54,7 +54,10 @@ public final class CompressedRTF extends LZWDecompresser {
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"{\\colortbl\\red0\\green0\\blue0\n\r\\par \\pard\\plain\\f0\\fs20\\b\\i\\u\\tab\\tx";
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public CompressedRTF() {
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super(true, 2);
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// Out flag has the normal meaning
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// Length wise, we're 2 longer than we say, so the max len is 18
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// Endian wise, we're big endian, so 0x1234 is pos 0x123
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super(true, 2, true);
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}
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public void decompress(InputStream src, OutputStream res) throws IOException {
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@ -80,17 +83,24 @@ public final class CompressedRTF extends LZWDecompresser {
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super.decompress(src, res);
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}
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/**
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* We use regular dictionary offsets, so no
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* need to change anything
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*/
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@Override
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protected int adjustDictionaryOffset(int offset) {
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// TODO Do we need to change anything?
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return 0;
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return offset;
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}
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@Override
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protected void populateDictionary(byte[] dict) {
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protected int populateDictionary(byte[] dict) {
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try {
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// Copy in the RTF constants
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byte[] preload = LZW_RTF_PRELOAD.getBytes("US-ASCII");
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System.arraycopy(preload, 0, dict, 0, preload.length);
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// Start adding new codes after the constants
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return preload.length;
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} catch(UnsupportedEncodingException e) {
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throw new RuntimeException("Your JVM is broken as it doesn't support US ASCII");
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}
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@ -93,7 +93,7 @@ public final class TestCompressedRTF extends TestCase {
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* Check that we can decode the first 8 codes
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* (1 flag byte + 8 codes)
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*/
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public void DISABLEDtestFirstBlock() throws Exception {
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public void testFirstBlock() throws Exception {
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HMEFMessage msg = new HMEFMessage(
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_samples.openResourceAsStream("quick-winmail.dat")
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);
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@ -112,7 +112,6 @@ public final class TestCompressedRTF extends TestCase {
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String decompStr = new String(decomp, "ASCII");
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// Test
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System.err.println(decompStr);
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assertEquals(block1.length(), decomp.length);
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assertEquals(block1, decompStr);
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}
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@ -121,7 +120,7 @@ System.err.println(decompStr);
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* Check that we can decode the first 16 codes
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* (flag + 8 codes, flag + 8 codes)
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*/
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public void DISABLEDtestFirstTwoBlocks() throws Exception {
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public void testFirstTwoBlocks() throws Exception {
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HMEFMessage msg = new HMEFMessage(
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_samples.openResourceAsStream("quick-winmail.dat")
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);
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@ -140,7 +139,6 @@ System.err.println(decompStr);
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String decompStr = new String(decomp, "ASCII");
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// Test
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System.err.println(decompStr);
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assertEquals(block2.length(), decomp.length);
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assertEquals(block2, decompStr);
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}
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