Better documentation for histogram bounds

Especially the inclusive end for the last range

Author: thomaskrause

core/src/annostorage/inmemory.rs

@@ -32,8 +32,12 @@ pub struct AnnoStorageImpl<T: Ord + Hash + Default> {
     anno_key_sizes: BTreeMap<AnnoKey, usize>,
     anno_keys: SymbolTable<AnnoKey>,
     anno_values: SymbolTable<String>,
-
-    /// additional statistical information
+    /// Sampled histograms for each annotation key .
+    /// Each histogram bound defines a range of values where we estimate that they have the same number of occurences.
+    ///
+    /// If h_i the the histogram bound value at index i, the first range is defined is as [h_0, h_1), the second range from [h_1, h_2) and so on.
+    /// Thus each element marks the inclusive start of a range and an exclusive end.
+    /// **The last range \[h_n-1, h_n\] has an inclusive upper bound instead of an exclusive one!**
     histogram_bounds: BTreeMap<usize, Vec<String>>,
     largest_item: Option<T>,
     total_number_of_annos: usize,

core/src/annostorage/ondisk.rs

@@ -48,7 +48,12 @@ where
 
     anno_key_sizes: BTreeMap<AnnoKey, usize>,
 
-    /// additional statistical information
+    /// Sampled histograms for each annotation key .
+    /// Each histogram bound defines a range of values where we estimate that they have the same number of occurences.
+    ///
+    /// If h_i the the histogram bound value at index i, the first range is defined is as [h_0, h_1), the second range from [h_1, h_2) and so on.
+    /// Thus each element marks the inclusive start of a range and an exclusive end.
+    /// **The last range \[h_n-1, h_n\] has an inclusive upper bound instead of an exclusive one!**
     histogram_bounds: BTreeMap<AnnoKey, Vec<String>>,
     largest_item: Option<T>,