aherbert commented on a change in pull request #140: Bloomfilter updates2
URL:
https://github.com/apache/commons-collections/pull/140#discussion_r391805516
##########
File path:
src/main/java/org/apache/commons/collections4/bloomfilter/hasher/Shape.java
##########
@@ -43,30 +43,32 @@
* [Wikipedia]</a>
* @since 4.5
*/
-public class Shape {
+public final class Shape {
/**
- * The natural logarithm of 2. Used in several calculations. approx
0.693147180
+ * The natural logarithm of 2. Used in several calculations. Approximately
0.693147180559945.
*/
private static final double LOG_OF_2 = Math.log(2.0);
/**
- * 1 / 2^log(2) approx -0.090619058. Used in calculating the number of
bits.
+ * log(1 / 2^log(2)). Used in calculating the number of bits.
Approximately -0.480453013918201.
Review comment:
I think -0.48 is correct:
[Wikipedia - Bloom Filter - Optimal number of hash
functions](https://en.wikipedia.org/wiki/Bloom_filter#Optimal_number_of_hash_functions)
```
m = - n ln(p) / ln(2)^2
```
So the denominator is -ln(2)^2 = -0.48.
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