LUCENE-6982: throw IAE on illegal bm25 parameter values

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1725350 13f79535-47bb-0310-9956-ffa450edef68

lucene/core/src/java/org/apache/lucene/search/similarities/BM25Similarity.java

@@ -44,8 +44,16 @@ public class BM25Similarity extends Similarity {
    * BM25 with the supplied parameter values.
    * @param k1 Controls non-linear term frequency normalization (saturation).
    * @param b Controls to what degree document length normalizes tf values.
+   * @throws IllegalArgumentException if {@code k1} is infinite or negative, or if {@code b} is 
+   *         not within the range {@code [0..1]}
    */
   public BM25Similarity(float k1, float b) {
+    if (Float.isFinite(k1) == false || k1 < 0) {
+      throw new IllegalArgumentException("illegal k1 value: " + k1 + ", must be a non-negative finite value");
+    }
+    if (Float.isNaN(b) || b < 0 || b > 1) {
+      throw new IllegalArgumentException("illegal b value: " + b + ", must be between 0 and 1");
+    }
     this.k1 = k1;
     this.b  = b;
   }
@@ -57,8 +65,7 @@ public class BM25Similarity extends Similarity {
    * </ul>
    */
   public BM25Similarity() {
-    this.k1 = 1.2f;
-    this.b  = 0.75f;
+    this(1.2f, 0.75f);
   }
   
   /** Implemented as <code>log(1 + (docCount - docFreq + 0.5)/(docFreq + 0.5))</code>. */

lucene/core/src/test/org/apache/lucene/search/similarities/TestBM25Similarity.java

@@ -33,4 +33,50 @@ public class TestBM25Similarity extends LuceneTestCase {
       }
     }
   }
+  
+  public void testIllegalK1() {
+    try {
+      new BM25Similarity(Float.POSITIVE_INFINITY, 0.75f);
+    } catch (IllegalArgumentException expected) {
+      assertTrue(expected.getMessage().contains("illegal k1 value"));
+    }
+    
+    try {
+      new BM25Similarity(-1, 0.75f);
+    } catch (IllegalArgumentException expected) {
+      assertTrue(expected.getMessage().contains("illegal k1 value"));
+    }
+    
+    try {
+      new BM25Similarity(Float.NaN, 0.75f);
+    } catch (IllegalArgumentException expected) {
+      assertTrue(expected.getMessage().contains("illegal k1 value"));
+    }
+  }
+  
+  public void testIllegalB() {
+    try {
+      new BM25Similarity(1.2f, 2f);
+    } catch (IllegalArgumentException expected) {
+      assertTrue(expected.getMessage().contains("illegal b value"));
+    }
+    
+    try {
+      new BM25Similarity(1.2f, -1f);
+    } catch (IllegalArgumentException expected) {
+      assertTrue(expected.getMessage().contains("illegal b value"));
+    }
+    
+    try {
+      new BM25Similarity(1.2f, Float.POSITIVE_INFINITY);
+    } catch (IllegalArgumentException expected) {
+      assertTrue(expected.getMessage().contains("illegal b value"));
+    }
+    
+    try {
+      new BM25Similarity(1.2f, Float.NaN);
+    } catch (IllegalArgumentException expected) {
+      assertTrue(expected.getMessage().contains("illegal b value"));
+    }
+  }
 }