Saturated bloomfilter size

README.md

@@ -77,7 +77,6 @@ See [Algebird's page on the Scaladex](https://index.scala-lang.org/twitter/algeb
 - [Scio](https://github.com/spotify/scio)
 - [Packetloop](https://www.packetloop.com) (see [this tweet](https://twitter.com/cloudjunky/status/355073917720858626))
 - Ebay uses Algebird for machine learning: [ScalaDays talk](http://www.slideshare.net/VitalyGordon/scalable-and-flexible-machine-learning-with-scala-linkedin)
-- [Apple (FEAR Team)](https://news.ycombinator.com/item?id=16969118)
 
 Other projects built with Algebird, as compiled by the Scaladex: [![Scaladex Dependents](https://index.scala-lang.org/count.svg?q=dependencies:twitter/algebird*&subject=scaladex:&color=blue&style=flat-square)](https://index.scala-lang.org/search?q=dependencies:twitter/algebird-core)
 

algebird-core/src/main/scala/com/twitter/algebird/BloomFilter.scala

@@ -157,13 +157,16 @@ object BloomFilter {
      * This is \hat{S}^{-1}(t) in the cardinality estimation paper used above.
      */
     def sInverse(t: Int): Double =
-      scala.math.log1p(-t.toDouble / width) / (numHashes * scala.math.log1p(-1.0 / width))
+      if (numBits == width) 0.0
+      else
+        scala.math.log(1 - t.toDouble / width) / (numHashes * scala.math.log1p(-1.0 / width))
 
     // Variable names correspond to those used in the paper.
     val t = numBits
     val n = sInverse(t).round.toInt
     // Take the min and max because the probability formula assumes
     // nl <= sInverse(t - 1) and sInverse(t + 1) <= nr
+
     val nl =
       scala.math.min(sInverse(t - 1).floor, (1 - approximationWidth) * n).toInt
     val nr =

algebird-test/src/test/scala/com/twitter/algebird/BloomFilterTest.scala

@@ -354,7 +354,6 @@ class BloomFilterTest extends WordSpec with Matchers {
         val items = (1 until exactCardinality).map { _.toString }
         val bf = bfMonoid.create(items: _*)
         val size = bf.size
-
         assert(size ~ exactCardinality)
         assert(size.min <= size.estimate)
         assert(size.max >= size.estimate)
@@ -410,6 +409,16 @@ class BloomFilterTest extends WordSpec with Matchers {
     }
   }
 
+  "BloomFilter method `size`" should {
+
+    "return the appropriate size when it's saturated " in {
+      val bfMonoid = BloomFilterMonoid[String](5, 13)
+      val strings = List(8, 9, 8, 10, 1, 8, 11, 12, 13, 14, 15, 67, 18981, 1122, 86787).map(_.toString)
+      val bf = bfMonoid.create(strings: _*)
+      assert(bf.size.isZero)
+    }
+  }
+
   "BloomFilter method `checkAndAdd`" should {
 
     "be identical to method `+`" in {