Author: tilman
Date: Wed Mar 12 17:05:03 2014
New Revision: 1576820
URL: http://svn.apache.org/r1576820
Log:
PDFBOX-1977: Check whether chunk needs adjusting before writing EOD
Modified:
pdfbox/trunk/pdfbox/src/main/java/org/apache/pdfbox/filter/LZWFilter.java
Modified:
pdfbox/trunk/pdfbox/src/main/java/org/apache/pdfbox/filter/LZWFilter.java
URL:
http://svn.apache.org/viewvc/pdfbox/trunk/pdfbox/src/main/java/org/apache/pdfbox/filter/LZWFilter.java?rev=1576820&r1=1576819&r2=1576820&view=diff
==============================================================================
--- pdfbox/trunk/pdfbox/src/main/java/org/apache/pdfbox/filter/LZWFilter.java
(original)
+++ pdfbox/trunk/pdfbox/src/main/java/org/apache/pdfbox/filter/LZWFilter.java
Wed Mar 12 17:05:03 2014
@@ -102,22 +102,8 @@ public class LZWFilter extends Filter
decoded.write(newData);
codeTable.add(newData);
}
- if (codeTable.size() >= 2047)
- {
- chunk = 12;
- }
- else if (codeTable.size() >= 1023)
- {
- chunk = 11;
- }
- else if (codeTable.size() >= 511)
- {
- chunk = 10;
- }
- else
- {
- chunk = 9;
- }
+
+ chunk = calculateChunk(codeTable.size());
prevCommand = nextCommand;
}
}
@@ -164,6 +150,7 @@ public class LZWFilter extends Filter
if (newFoundCode == -1)
{
// use previous
+ chunk = calculateChunk(codeTable.size() - 1);
out.writeBits(foundCode, chunk);
// create new table entry
codeTable.add(inputPattern);
@@ -187,29 +174,22 @@ public class LZWFilter extends Filter
foundCode = newFoundCode;
}
}
- if (codeTable.size() - 1 >= 2047)
- {
- chunk = 12;
- }
- else if (codeTable.size() - 1 >= 1023)
- {
- chunk = 11;
- }
- else if (codeTable.size() - 1 >= 511)
- {
- chunk = 10;
- }
- else
- {
- chunk = 9;
- }
}
if (foundCode != -1)
{
+ chunk = calculateChunk(codeTable.size() - 1);
out.writeBits(foundCode, chunk);
}
+
+ // PPDFBOX-1977: the decoder wouldn't know that the encoder would
output
+ // an EOD as code, so he would have increased his own code table and
+ // possibly adjusted the chunk. Therefore, the encoder must behave as
+ // if the code table had just grown and thus it must be checked it is
+ // needed to adjust the chunk, based on an increased table size
parameter
+ chunk = calculateChunk(codeTable.size());
+
out.writeBits(EOD, chunk);
- out.writeBits(0, 7);
+ out.writeBits(0, 7); // pad with 0
out.flush(); // must do or file will be empty :-(
codeTable.clear();
}
@@ -270,4 +250,28 @@ public class LZWFilter extends Filter
codeTable.add(null); // 256 EOD
codeTable.add(null); // 257 CLEAR_TABLE
}
+
+ /**
+ * Calculate the appropriate chunk size
+ *
+ * @param tabSize the size of the code table
+ *
+ * @return a value between 9 and 12
+ */
+ private int calculateChunk(int tabSize)
+ {
+ if (tabSize >= 2047)
+ {
+ return 12;
+ }
+ if (tabSize >= 1023)
+ {
+ return 11;
+ }
+ if (tabSize >= 511)
+ {
+ return 10;
+ }
+ return 9;
+ }
}
