Author: tilman Date: Wed Mar 12 17:05:28 2014 New Revision: 1576821 URL: http://svn.apache.org/r1576821 Log: PDFBOX-1977: Check whether chunk needs adjusting before writing EOD
Modified: pdfbox/branches/1.8/pdfbox/src/main/java/org/apache/pdfbox/filter/LZWFilter.java Modified: pdfbox/branches/1.8/pdfbox/src/main/java/org/apache/pdfbox/filter/LZWFilter.java URL: http://svn.apache.org/viewvc/pdfbox/branches/1.8/pdfbox/src/main/java/org/apache/pdfbox/filter/LZWFilter.java?rev=1576821&r1=1576820&r2=1576821&view=diff ============================================================================== --- pdfbox/branches/1.8/pdfbox/src/main/java/org/apache/pdfbox/filter/LZWFilter.java (original) +++ pdfbox/branches/1.8/pdfbox/src/main/java/org/apache/pdfbox/filter/LZWFilter.java Wed Mar 12 17:05:28 2014 @@ -105,22 +105,8 @@ public class LZWFilter implements Filter result.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; } } @@ -168,6 +154,7 @@ public class LZWFilter implements Filter if (newFoundCode == -1) { // use previous + chunk = calculateChunk(codeTable.size() - 1); out.writeBits(foundCode, chunk); // create new table entry codeTable.add(inputPattern); @@ -191,29 +178,22 @@ public class LZWFilter implements 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(); } @@ -275,4 +255,27 @@ public class LZWFilter implements Filter 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; + } }