feat: Add Podeidon::hades_permutation (#58)

Author: fmoletta

crates/starknet-types-core/src/hash/poseidon.rs

@@ -30,6 +30,18 @@ impl StarkHash for Poseidon {
     }
 }
 
+impl Poseidon {
+    /// Computes the Hades permutation over a mutable state of 3 Felts, as defined
+    /// in <https://docs.starknet.io/documentation/architecture_and_concepts/Cryptography/hash-functions/#poseidon_array_hash>
+    pub fn hades_permutation(state: &mut [Felt; 3]) {
+        let mut state_inner = [state[0].0, state[1].0, state[2].0];
+        PoseidonCairoStark252::hades_permutation(&mut state_inner);
+        for i in 0..3 {
+            state[i] = Felt(state_inner[i]);
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -60,4 +72,24 @@ mod tests {
                 .unwrap();
         assert_eq!(Poseidon::hash_array(&[a, b, c]), expected);
     }
+
+    #[test]
+    fn test_hades_permutation() {
+        let mut state = [
+            Felt::from_hex("0x9").unwrap(),
+            Felt::from_hex("0xb").unwrap(),
+            Felt::from_hex("0x2").unwrap(),
+        ];
+        let expected = [
+            Felt::from_hex("0x510f3a3faf4084e3b1e95fd44c30746271b48723f7ea9c8be6a9b6b5408e7e6")
+                .unwrap(),
+            Felt::from_hex("0x4f511749bd4101266904288021211333fb0a514cb15381af087462fa46e6bd9")
+                .unwrap(),
+            Felt::from_hex("0x186f6dd1a6e79cb1b66d505574c349272cd35c07c223351a0990410798bb9d8")
+                .unwrap(),
+        ];
+        Poseidon::hades_permutation(&mut state);
+
+        assert_eq!(state, expected);
+    }
 }