feat: pedersen hasher type (#684)

starknet-crypto/src/lib.rs

@@ -33,7 +33,7 @@ mod test_utils;
 
 pub use starknet_types_core::felt::Felt;
 
-pub use pedersen_hash::pedersen_hash;
+pub use pedersen_hash::{pedersen_hash, PedersenHasher};
 
 pub use poseidon_hash::{
     poseidon_hash, poseidon_hash_many, poseidon_hash_single, poseidon_permute_comp, PoseidonHasher,

starknet-crypto/src/pedersen_hash/mod.rs

@@ -1,3 +1,5 @@
+use starknet_types_core::felt::Felt;
+
 #[cfg(not(feature = "pedersen_no_lookup"))]
 mod default;
 #[cfg(not(feature = "pedersen_no_lookup"))]
@@ -8,6 +10,31 @@ mod no_lookup;
 #[cfg(feature = "pedersen_no_lookup")]
 pub use no_lookup::pedersen_hash;
 
+/// A stateful hasher for Starknet Pedersen hash.
+#[derive(Debug, Default)]
+pub struct PedersenHasher {
+    hash: Felt,
+    len: usize,
+}
+
+impl PedersenHasher {
+    /// Creates a new [`PedersenHasher`].
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Absorbs message into the hash.
+    pub fn update(&mut self, msg: Felt) {
+        self.hash = pedersen_hash(&self.hash, &msg);
+        self.len += 1;
+    }
+
+    /// Finishes and returns hash.
+    pub fn finalize(&self) -> Felt {
+        pedersen_hash(&self.hash, &self.len.into())
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;