srtm30 utils

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

@@ -0,0 +1,57 @@
+/**
+ * DataInputStream for decoding fast-compact encoded number sequences
+ *
+ * @author ab
+ */
+package btools.util;
+
+import java.io.DataInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+
+
+public final class MixCoderDataInputStream extends DataInputStream
+{
+  private long lastValue;
+  private long repCount;
+
+  public MixCoderDataInputStream( InputStream is )
+  {
+    super( is );
+  }
+
+  public long readSigned() throws IOException
+  {
+    long v = readUnsigned();
+    return ( v & 1 ) == 0 ? v >> 1 : -(v >> 1 );
+  }
+
+  public long readUnsigned() throws IOException
+  {
+    long v = 0;
+    int shift = 0;
+    for(;;)
+    {
+      long i7 = readByte() & 0xff;
+      v |= (( i7 & 0x7f ) << shift);
+      if ( ( i7 & 0x80 ) == 0 ) break;
+      shift += 7;
+    }
+    return v;
+  }
+
+  public long readMixed() throws IOException
+  {
+    if ( repCount == 0 )
+    {
+      long b = readByte() & 0xff;
+      long repCode = b >> 6;
+      long diffcode = b & 0x3f;
+      repCount = repCode == 0 ?  readUnsigned() : repCode;
+      lastValue += diffcode == 0 ? readSigned() : diffcode - 32;
+    }
+    repCount--;
+    return lastValue;
+  }
+
+}