add serialization and deserialization for BytesHash (#1645)

* add serialization and deserialization for BytesHash

* fix cargo clippy precedence errors

---------

Co-authored-by: fdecroix <fdecroix@eryx.co>

field/src/types.rs

@@ -369,7 +369,7 @@ pub trait Field:
         let mut product = Self::ONE;
 
         for j in 0..bits_u64(power) {
-            if (power >> j & 1) != 0 {
+            if ((power >> j) & 1) != 0 {
                 product *= current;
             }
             current = current.square();

plonky2/src/gadgets/arithmetic_extension.rs

@@ -470,7 +470,7 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
             if j != 0 {
                 current = self.square_extension(current);
             }
-            if (exponent >> j & 1) != 0 {
+            if ((exponent >> j) & 1) != 0 {
                 product = self.mul_extension(product, current);
             }
         }

plonky2/src/hash/hash_types.rs

@@ -1,7 +1,9 @@
 #[cfg(not(feature = "std"))]
 use alloc::vec::Vec;
+use core::fmt;
 
 use anyhow::ensure;
+use serde::de::{self, Visitor};
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
 
 use crate::field::goldilocks_field::GoldilocksField;
@@ -193,19 +195,52 @@ impl<F: RichField, const N: usize> GenericHashOut<F> for BytesHash<N> {
 }
 
 impl<const N: usize> Serialize for BytesHash<N> {
-    fn serialize<S>(&self, _serializer: S) -> Result<S::Ok, S::Error>
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
         S: Serializer,
     {
-        todo!()
+        serializer.serialize_bytes(&self.0)
+    }
+}
+
+struct ByteHashVisitor<const N: usize>;
+
+impl<'de, const N: usize> Visitor<'de> for ByteHashVisitor<N> {
+    type Value = BytesHash<N>;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        write!(formatter, "an array containing exactly {} bytes", N)
+    }
+
+    fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+    where
+        A: de::SeqAccess<'de>,
+    {
+        let mut bytes = [0u8; N];
+        for i in 0..N {
+            let next_element = seq.next_element()?;
+            match next_element {
+                Some(value) => bytes[i] = value,
+                None => return Err(de::Error::invalid_length(i, &self)),
+            }
+        }
+        Ok(BytesHash(bytes))
+    }
+
+    fn visit_bytes<E>(self, s: &[u8]) -> Result<Self::Value, E>
+    where
+        E: de::Error,
+    {
+        let bytes = s.try_into().unwrap();
+        Ok(BytesHash(bytes))
     }
 }
 
 impl<'de, const N: usize> Deserialize<'de> for BytesHash<N> {
-    fn deserialize<D>(_deserializer: D) -> Result<Self, D::Error>
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
         D: Deserializer<'de>,
     {
-        todo!()
+        deserializer.deserialize_seq(ByteHashVisitor::<N>)
     }
 }