srtm1 progress

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

@@ -12,46 +12,74 @@ import java.io.InputStream;
 
 public final class MixCoderDataInputStream extends DataInputStream
 {
-  private long lastValue;
-  private long repCount;
+  private int lastValue;
+  private int repCount;
+  private int diffshift;
+
+  private int bm = 0x100;
+  private int b;
 
   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
+  public int 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;
+      boolean negative = decodeBit();
+      int d = decodeVarBits() + diffshift;
+      repCount = decodeVarBits() + 1;
+      lastValue += negative ? -d : d;
+      diffshift = 1;
     }
     repCount--;
     return lastValue;
   }
 
+  public final boolean decodeBit() throws IOException
+  {
+    if ( bm == 0x100 )
+    {
+      bm = 1;
+      b = readByte();
+    }
+    boolean value = ( ( b & bm ) != 0 );
+    bm <<= 1;
+    return value;
+  }
+
+  public final int decodeVarBits() throws IOException
+  {
+    int range = 0;
+    int value = 0;
+    while (!decodeBit())
+    {
+      value += range + 1;
+      range = 2 * range + 1;
+    }
+    return value + decodeBounded( range );
+  }
+
+
+  public final int decodeBounded( int max ) throws IOException
+  {
+    int value = 0;
+    int im = 1; // integer mask
+    while (( value | im ) <= max)
+    {
+      if ( bm == 0x100 )
+      {
+        bm = 1;
+        b = readByte();
+      }
+      if ( ( b & bm ) != 0 )
+        value |= im;
+      bm <<= 1;
+      im <<= 1;
+    }
+    return value;
+  }
+
 }