added crc logic for datafile access

brouter-mapaccess/src/main/java/btools/mapaccess/PhysicalFile.java

@@ -0,0 +1,69 @@
+/**
+ * cache for a single square
+ *
+ * @author ab
+ */
+package btools.mapaccess;
+
+import java.io.*;
+import btools.util.Crc32;
+
+final class PhysicalFile
+{
+  RandomAccessFile ra = null;
+  long[] fileIndex = new long[25];
+  int[] fileHeaderCrcs;
+   
+  private int fileIndexCrc;
+  public long creationTime;
+
+  String fileName;
+  
+  public PhysicalFile( File f, byte[] iobuffer, int lookupVersion ) throws Exception
+  {
+    fileName = f.getName();
+
+    ra = new RandomAccessFile( f, "r" );
+    ra.readFully( iobuffer, 0, 200 );
+    fileIndexCrc = Crc32.crc( iobuffer, 0, 200 );
+    ByteDataReader dis = new ByteDataReader( iobuffer );
+    for( int i=0; i<25; i++ )
+    {
+      long lv = dis.readLong();
+      short readVersion = (short)(lv >> 48);
+      if ( readVersion != lookupVersion )
+      {
+        throw new IllegalArgumentException( "lookup version mismatch (old rd5?) lookups.dat="
+                 + lookupVersion + " " + f. getAbsolutePath() + "=" + readVersion );
+      }
+      fileIndex[i] = lv & 0xffffffffffffL;
+    }
+
+    // read some extra info from the end of the file, if present
+    long len = ra.length();
+
+    long pos = fileIndex[24];
+    int extraLen = 8 + 26*4;
+
+    if ( len == pos ) return; // old format o.k.
+
+    if ( len < pos+extraLen ) // > is o.k. for future extensions!
+    {
+      throw new IOException( "file of size " + len + " + too short, should be " + (pos+extraLen) );
+    }
+    
+    ra.seek( pos );
+    ra.readFully( iobuffer, 0, extraLen );
+    dis = new ByteDataReader( iobuffer );
+    creationTime = dis.readLong();
+    if ( dis.readInt() != fileIndexCrc )
+    {
+      throw new IOException( "top index checksum error" );
+    }
+    fileHeaderCrcs = new int[25];
+    for( int i=0; i<25; i++ )
+    {
+      fileHeaderCrcs[i] = dis.readInt();
+    }
+  }
+}