Merge pull request #37 from SidWeng/master

get the filter element size

Author: alexandrnikitin

bloom-filter/src/main/scala/bloomfilter/mutable/BloomFilter.scala

@@ -1,6 +1,7 @@
 package bloomfilter.mutable
 
 import java.io.{DataInputStream, DataOutputStream, InputStream, OutputStream}
+import scala.math._
 
 import bloomfilter.CanGenerateHashFrom
 
@@ -62,6 +63,12 @@ class BloomFilter[T] private (val numberOfBits: Long, val numberOfHashes: Int, p
  bits.writeTo(out)
  }
 
+ def approximateElementCount(): Long = {
+ val bitCount = bits.getBitCount
+
+ val fractionOfBitsSet = (bitCount / numberOfBits).toDouble
+ return round(-log1p(-(fractionOfBitsSet)) * numberOfBits / numberOfHashes)
+ }
 
  def dispose(): Unit = bits.dispose()
 

bloom-filter/src/main/scala/bloomfilter/mutable/UnsafeBitArray.scala

@@ -10,6 +10,7 @@ class UnsafeBitArray(val numberOfBits: Long) extends Serializable {
  @transient
  private val ptr = unsafe.allocateMemory(8L * indices)
  unsafe.setMemory(ptr, 8L * indices, 0.toByte)
+ private var bitCount = 0L
 
  def get(index: Long): Boolean = {
  (unsafe.getLong(ptr + (index >>> 6) * 8L) & (1L << index)) != 0
@@ -20,6 +21,7 @@ class UnsafeBitArray(val numberOfBits: Long) extends Serializable {
  val long = unsafe.getLong(offset)
  if ((long & (1L << index)) == 0) {
  unsafe.putLong(offset, long | (1L << index))
+ bitCount += 1
  }
  }
 
@@ -49,7 +51,7 @@ class UnsafeBitArray(val numberOfBits: Long) extends Serializable {
  }
 
  def getBitCount: Long = {
- throw new NotImplementedError("Not implemented yet")
+ bitCount
  }
 
  def writeTo(out: OutputStream): Unit = {