Use width_lim instead of bucket_lim

libraries/persistent_store/fuzz/src/histogram.rs

@@ -33,12 +33,7 @@ impl Histogram {
     ///
     /// The bucket of `item` is the highest power of two, lower or equal to `item`. If `item` is
     /// zero, then its bucket is also zero.
-    ///
-    /// # Panics
-    ///
-    /// Panics if the item is too big, i.e. it uses its most significant bit.
     pub fn add(&mut self, item: usize) {
-        assert!(item <= usize::max_value() / 2);
         *self.buckets.entry(get_bucket(item)).or_insert(0) += 1;
     }
 
@@ -49,15 +44,12 @@ impl Histogram {
         }
     }
 
-    /// Returns one past the highest non-empty bucket.
+    /// Returns the bit-width of one past the highest non-empty bucket.
     ///
-    /// In other words, all non-empty buckets of the histogram are smaller than the returned bucket.
-    pub fn bucket_lim(&self) -> usize {
-        match self.buckets.keys().max() {
-            None => 0,
-            Some(0) => 1,
-            Some(x) => 2 * x,
-        }
+    /// In other words, all non-empty buckets of the histogram have a bit-width smaller than the
+    /// returned width.
+    pub fn width_lim(&self) -> usize {
+        self.buckets.keys().max().map_or(0, |&x| num_bits(x) + 1)
     }
 
     /// Returns the count of a bucket.

libraries/persistent_store/fuzz/src/stats.rs

@@ -17,7 +17,6 @@
 //! This is not used during actual fuzzing, only when replaying a corpus to compute statistics.
 
 use crate::histogram::{bucket_from_width, Histogram};
-use crate::num_bits;
 use std::collections::HashMap;
 use strum::{Display, EnumIter, EnumString, IntoEnumIterator};
 
@@ -110,13 +109,14 @@ impl Stats {
         self.stats.get(&key).and_then(|h| h.get(bucket))
     }
 
-    /// Returns one past the highest non-empty bucket.
+    /// Returns the bit-width of one past the highest non-empty bucket.
     ///
-    /// In other words, all non-empty buckets of the histogram are smaller than the returned bucket.
-    fn bucket_lim(&self) -> usize {
+    /// In other words, all non-empty buckets of the histogram have a bit-width smaller than the
+    /// returned width.
+    fn width_lim(&self) -> usize {
         self.stats
             .values()
-            .map(|h| h.bucket_lim())
+            .map(|h| h.width_lim())
             .max()
             .unwrap_or(0)
     }
@@ -125,10 +125,10 @@ impl Stats {
 impl std::fmt::Display for Stats {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
         let mut matrix: Vec<Vec<String>> = Vec::new();
+        let bits = self.width_lim();
 
         let mut header = Vec::new();
         header.push(String::new());
-        let bits = num_bits(self.bucket_lim());
         for width in 0..bits {
             header.push(format!(" {}", bucket_from_width(width)));
         }