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Add subtract to MultiHash #605

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Add subtract to MultiHash #605

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7 changes: 7 additions & 0 deletions fastcrypto/src/hash.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -234,6 +234,9 @@ pub trait MultisetHash<const DIGEST_LENGTH: usize>: Eq {
/// Add all the elements of another hash function into this hash function.
fn union(&mut self, other: &Self);

/// Remove all the elements of another hash function from this hash function.
fn subtract(&mut self, other: &Self);

// Note that the "remove" operation is safe even if an item has been removed
// more times than it has been inserted. To see why, consider the following
// example: Suppose an adversary has performed two sets of "insert(x)" and
Expand Down Expand Up @@ -302,6 +305,10 @@ impl MultisetHash<32> for EllipticCurveMultisetHash {
self.accumulator += other.accumulator;
}

fn subtract(&mut self, other: &Self) {
self.accumulator -= other.accumulator;
}

fn remove<Data: AsRef<[u8]>>(&mut self, item: Data) {
self.accumulator -= Self::hash_to_point(item);
}
Expand Down