Change Similarity to use SmallFloat for norm encoding

git-svn-id: https://svn.apache.org/repos/asf/lucene/java/trunk@349074 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/lucene/search/Similarity.java

@@ -27,7 +27,7 @@ import org.apache.lucene.index.Term;
 import org.apache.lucene.index.IndexReader;       // for javadoc
 import org.apache.lucene.index.IndexWriter;       // for javadoc
 import org.apache.lucene.document.Field;          // for javadoc
-
+import org.apache.lucene.util.SmallFloat;
 
 /** Expert: Scoring API.
  * <p>Subclasses implement search scoring.
@@ -116,7 +116,7 @@ public abstract class Similarity implements Serializable {
 
   static {
     for (int i = 0; i < 256; i++)
-      NORM_TABLE[i] = byteToFloat((byte)i);
+      NORM_TABLE[i] = SmallFloat.byte315ToFloat((byte)i);
   }
 
   /** Decodes a normalization factor stored in an index.
@@ -170,7 +170,8 @@ public abstract class Similarity implements Serializable {
 
   /** Encodes a normalization factor for storage in an index.
    *
-   * <p>The encoding uses a five-bit exponent and three-bit mantissa, thus
+   * <p>The encoding uses a three-bit mantissa, a five-bit exponent, and
+   * the zero-exponent point at 15, thus
    * representing values from around 7x10^9 to 2x10^-9 with about one
    * significant decimal digit of accuracy.  Zero is also represented.
    * Negative numbers are rounded up to zero.  Values too large to represent
@@ -179,42 +180,10 @@ public abstract class Similarity implements Serializable {
    * value.
    *
    * @see Field#setBoost(float)
+   * @see SmallFloat
    */
   public static byte encodeNorm(float f) {
-    return floatToByte(f);
+    return SmallFloat.floatToByte315(f);
-  }
-
-  private static float byteToFloat(byte b) {
-    if (b == 0)                                   // zero is a special case
-      return 0.0f;
-    int mantissa = b & 7;
-    int exponent = (b >> 3) & 31;
-    int bits = ((exponent+(63-15)) << 24) | (mantissa << 21);
-    return Float.intBitsToFloat(bits);
-  }
-
-  private static byte floatToByte(float f) {
-    if (f < 0.0f)                                 // round negatives up to zero
-      f = 0.0f;
-
-    if (f == 0.0f)                                // zero is a special case
-      return 0;
-
-    int bits = Float.floatToIntBits(f);           // parse float into parts
-    int mantissa = (bits & 0xffffff) >> 21;
-    int exponent = (((bits >> 24) & 0x7f) - 63) + 15;
-
-    if (exponent > 31) {                          // overflow: use max value
-      exponent = 31;
-      mantissa = 7;
-    }
-
-    if (exponent < 0) {                           // underflow: use min value
-      exponent = 0;
-      mantissa = 1;
-    }
-
-    return (byte)((exponent << 3) | mantissa);    // pack into a byte
   }
 
 

src/test/org/apache/lucene/util/TestSmallFloat.java

@@ -76,7 +76,6 @@ public class TestSmallFloat extends TestCase {
 
   public void testFloatToByte() {
     Random rand = new Random(0);
-    rand.nextFloat();
     // up iterations for more exhaustive test after changing something
     for (int i=0; i<100000; i++) {
       float f = Float.intBitsToFloat(rand.nextInt());
@@ -93,7 +92,23 @@ public class TestSmallFloat extends TestCase {
     }
   }
 
-
+  /***
-
+  // Do an exhaustive test of all possible floating point values
+  // for the 315 float against the original norm encoding in Similarity.
+  // Takes 75 seconds on my Pentium4 3GHz, with Java5 -server
+  public void testAllFloats() {
+    for(int i = Integer.MIN_VALUE;;i++) {
+      float f = Float.intBitsToFloat(i);
+      if (f==f) { // skip non-numbers
+        byte b1 = orig_floatToByte(f);
+        byte b2 = SmallFloat.floatToByte315(f);
+        if (b1!=b2) {
+          TestCase.fail("Failed floatToByte315 for float " + f);
+        }
+      }
+      if (i==Integer.MAX_VALUE) break;
+    }
+  }
+  ***/
 
 }