srtm30 utils

brouter-util/src/main/java/btools/util/MixCoderDataOutputStream.java

@@ -0,0 +1,79 @@
+/**
+ * DataOutputStream for fast-compact encoding of number sequences
+ *
+ * @author ab
+ */
+package btools.util;
+
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+
+
+public final class MixCoderDataOutputStream extends DataOutputStream
+{
+  private long lastValue;
+  private long lastLastValue;
+  private long repCount;
+  private boolean doFlush;
+
+  public MixCoderDataOutputStream( OutputStream os )
+  {
+     super( os );
+  }
+
+  public void writeSigned( long v ) throws IOException
+  {
+    writeUnsigned( v < 0 ? ( (-v) << 1 ) | 1 : v << 1 );
+  }
+
+  public void writeUnsigned( long v ) throws IOException
+  {
+    if ( v < 0 ) throw new IllegalArgumentException(  "writeUnsigned: " + v );
+    do
+    {
+      long i7 = v & 0x7f;
+      v >>= 7;
+      if ( v != 0 ) i7 |= 0x80;
+      writeByte( (byte)( i7 & 0xff ) );
+    }
+    while( v != 0 );
+  }
+
+  public void writeMixed( long v ) throws IOException
+  {
+    if ( v != lastValue && repCount > 0 )
+    {
+      long d = lastValue - lastLastValue;
+      lastLastValue = lastValue;
+
+      // if diff fits within 6 bits and rep-count < 4, write a single byte
+      int repCode = repCount < 4 ? (int)repCount : 0;
+      int diffcode = (int)(d > -32 && d < 32 ? d+32 : 0);
+
+      writeByte( (byte)( diffcode | repCode << 6 ) );
+      if ( repCode == 0)
+      {
+        writeUnsigned( repCount );
+      }
+      if ( diffcode == 0)
+      {
+        writeSigned( d );
+      }
+      repCount = 0;
+    }
+    lastValue = v;
+    repCount++;
+  }
+
+  @Override
+  public void flush() throws IOException
+  {
+    // todo: does this keep stream consistency after flush ?
+    long v = lastValue;
+    writeMixed( v+1 );
+    lastValue = v;
+    repCount = 0;
+  }
+
+}