Revision: 5968
http://jnode.svn.sourceforge.net/jnode/?rev=5968&view=rev
Author: galatnm
Date: 2013-02-20 12:01:01 +0000 (Wed, 20 Feb 2013)
Log Message:
-----------
Better implementation of mapVcnToLcn() for compressed data runs. (Luke Quinane)
Modified Paths:
--------------
trunk/fs/src/fs/org/jnode/fs/ntfs/CompressedDataRun.java
Modified: trunk/fs/src/fs/org/jnode/fs/ntfs/CompressedDataRun.java
===================================================================
--- trunk/fs/src/fs/org/jnode/fs/ntfs/CompressedDataRun.java 2013-02-20
11:56:05 UTC (rev 5967)
+++ trunk/fs/src/fs/org/jnode/fs/ntfs/CompressedDataRun.java 2013-02-20
12:01:01 UTC (rev 5968)
@@ -224,7 +224,19 @@
@Override
public long mapVcnToLcn(long vcn) {
- return compressedRun.mapVcnToLcn(vcn);
+ // This is the actual number of stored clusters after compression.
+ // If the number of stored clusters is the same as the compression
unit size,
+ // then the data can be read directly without decompressing it.
+ final int compClusters = compressedRun.getLength();
+ if (compClusters == compressionUnitSize) {
+ return compressedRun.mapVcnToLcn(vcn);
+ }
+
+ // Now we know the data is compressed. Map the VCN to the
corresponding compressed block...
+ final long actFirstVcn = Math.max(compressedRun.getFirstVcn(), vcn);
+ final int vcnOffsetWithinUnit = (int) (actFirstVcn %
compressionUnitSize);
+ final long compFirstVcn = actFirstVcn - vcnOffsetWithinUnit;
+ return compressedRun.mapVcnToLcn(compFirstVcn);
}
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