diff --git a/src/trace/implementations/rhh.rs b/src/trace/implementations/rhh.rs index 64cac268b..088055507 100644 --- a/src/trace/implementations/rhh.rs +++ b/src/trace/implementations/rhh.rs @@ -113,7 +113,9 @@ mod val_batch { /// would most like to end up. The `BatchContainer` trait does not provide a `capacity()` method, /// otherwise we would just use that. pub key_capacity: usize, - pub divisor: usize, + /// A number large enough that when it divides any `u64` the result is at most `self.key_capacity`. + /// When that capacity is zero or one, this is set to zero instead. + pub divisor: u64, /// The number of present keys, distinct from `keys.len()` which contains pub key_count: usize, @@ -194,8 +196,10 @@ mod val_batch { /// Indicates both the desired location and the hash signature of the key. fn desired_location(&self, key: &K) -> usize { - let hash: usize = key.hashed().into().try_into().unwrap(); - hash / self.divisor + if self.divisor == 0 { 0 } + else { + (key.hashed().into() / self.divisor).try_into().expect("divisor not large enough to force u64 into uisze") + } } /// Returns true if one should advance one's index in the search for `key`. @@ -216,11 +220,15 @@ mod val_batch { } } - // I hope this works out; meant to be 2^64 / self.key_capacity, so that dividing - // `signature` by this gives something in `[0, self.key_capacity)`. We could also - // do powers of two and just make this really easy. - fn divisor_for_capacity(capacity: usize) -> usize { - if capacity == 0 { 0 } + /// A value large enough that any `u64` divided by it is less than `capacity`. + /// + /// This is `2^64 / capacity`, except in the cases where `capacity` is zero or one. + /// In those cases, we'll return `0` to communicate the exception, for which we should + /// just return `0` when announcing a target location (and a zero capacity that we insert + /// into becomes a bug). + fn divisor_for_capacity(capacity: usize) -> u64 { + let capacity: u64 = capacity.try_into().expect("usize exceeds u64"); + if capacity == 0 || capacity == 1 { 0 } else { ((1 << 63) / capacity) << 1 }