pre-process speed: fast binary also for 90m srtm

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

@@ -9,8 +9,8 @@ public class BitCoderContext
   private int bits; // bits left in buffer
   private int b; // buffer word
 
-  private static final int[] vl_values = new int[4096];
-  private static final int[] vl_length = new int[4096];
+  public static final int[] vl_values = new int[4096];
+  public static final int[] vl_length = new int[4096];
 
   private static final int[] vc_values = new int[4096];
   private static final int[] vc_length = new int[4096];

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

@@ -16,8 +16,11 @@ public final class MixCoderDataInputStream extends DataInputStream
   private int repCount;
   private int diffshift;
 
-  private int bm = 0x100;
-  private int b;
+  private int bits; // bits left in buffer
+  private int b; // buffer word
+
+  private static final int[] vl_values = BitCoderContext.vl_values;
+  private static final int[] vl_length = BitCoderContext.vl_length;
 
   public MixCoderDataInputStream( InputStream is )
   {
@@ -40,46 +43,99 @@ public final class MixCoderDataInputStream extends DataInputStream
 
   public final boolean decodeBit() throws IOException
   {
-    if ( bm == 0x100 )
-    {
-      bm = 1;
-      b = readByte();
-    }
-    boolean value = ( ( b & bm ) != 0 );
-    bm <<= 1;
+    fillBuffer();
+    boolean value = ( ( b & 1 ) != 0 );
+    b >>>= 1;
+    bits--;
     return value;
   }
 
-  public final int decodeVarBits() throws IOException
+  public final int decodeVarBits2() throws IOException
   {
     int range = 0;
-    int value = 0;
     while (!decodeBit())
     {
-      value += range + 1;
       range = 2 * range + 1;
     }
-    return value + decodeBounded( range );
+    return range + decodeBounded( range );
   }
 
-
+  /**
+   * decode an integer in the range 0..max (inclusive).
+   * @see #encodeBounded
+   */
   public final int decodeBounded( int max ) throws IOException
   {
     int value = 0;
     int im = 1; // integer mask
     while (( value | im ) <= max)
     {
-      if ( bm == 0x100 )
+      if ( decodeBit() )
       {
-        bm = 1;
-        b = readByte();
-      }
-      if ( ( b & bm ) != 0 )
         value |= im;
-      bm <<= 1;
+      }
       im <<= 1;
     }
     return value;
   }
 
+
+  /**
+   * @see #encodeVarBits
+   */
+
+  public final int decodeVarBits() throws IOException
+  {
+    fillBuffer();
+    int b12 = b & 0xfff;
+    int len = vl_length[b12];
+    if ( len <= 12 )
+    {
+      b >>>= len;
+      bits -= len;
+      return vl_values[b12]; // full value lookup
+    }
+    if ( len <= 23 ) // // only length lookup
+    {
+      int len2 = len >> 1;
+      b >>>= (len2+1);
+      int mask = 0xffffffff >>> ( 32 - len2 );
+      mask += b & mask;
+      b >>>= len2;
+      bits -= len;
+      return mask;
+    }
+    if ( (b & 0xffffff) != 0 )
+    {
+      // here we just know len in [25..47]
+      // ( fillBuffer guarantees only 24 bits! )
+      b >>>= 12;
+      int len3 = 1 + (vl_length[b & 0xfff]>>1);
+      b >>>= len3;
+      int len2 = 11 + len3;
+      bits -= len2+1;
+      fillBuffer();
+      int mask = 0xffffffff >>> ( 32 - len2 );
+      mask += b & mask;
+      b >>>= len2;
+      bits -= len2;
+      return mask;
+    }
+    return decodeVarBits2(); // no chance, use the slow one
+  }
+
+  private void fillBuffer() throws IOException
+  {
+    while (bits < 24)
+    {
+      int nextByte = read();
+      
+      if ( nextByte != -1 )
+      {
+        b |= (nextByte & 0xff) << bits;
+      }
+      bits += 8;
+    }
+  }
+
 }