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perf: iterate counts[] in value_at_quantile to elide bounds checks #139

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perf: iterate counts[] in value_at_quantile to elide bounds checks #139

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9 changes: 5 additions & 4 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1350,11 +1350,12 @@ impl<T: Counter> Histogram<T> {
count_at_quantile = 1;
}

// Iterate the slice directly so the element is handed to the loop without a
// per-element bounds check on the hot prefix-sum path.
// TODO overflow
let mut total_to_current_index: u64 = 0;
for i in 0..self.counts.len() {
// Direct indexing is safe; indexes must reside in counts array.
// TODO overflow
total_to_current_index += self.counts[i].as_u64();
for (i, count) in self.counts.iter().enumerate() {
total_to_current_index += count.as_u64();
if total_to_current_index >= count_at_quantile {
let value_at_index = self.value_for(i);
return if quantile == 0.0 {
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