Fix a bug inside StdArray serialization logic

It is not correct to use $BITS/8 to define the slice size and having a test that uses BA3 demonstrates that.

This changes it to use serializable size instead

ipa-core/src/secret_sharing/vector/array.rs

@@ -6,7 +6,7 @@ use std::{
 };
 
 use generic_array::{ArrayLength, GenericArray};
-use typenum::{U16, U256, U32, U64};
+use typenum::{Unsigned, U16, U256, U32, U64};
 
 use crate::{
     const_assert_eq,
@@ -353,7 +353,7 @@ macro_rules! impl_serializable {
             type DeserializationError = <V as Serializable>::DeserializationError;
 
             fn serialize(&self, buf: &mut GenericArray<u8, Self::Size>) {
-                let sz: usize = (<V as SharedValue>::BITS / 8).try_into().unwrap();
+                let sz: usize = <V as Serializable>::Size::USIZE;
                 for i in 0..$width {
                     self.0[i].serialize(
                         GenericArray::try_from_mut_slice(&mut buf[sz * i..sz * (i + 1)]).unwrap(),
@@ -364,7 +364,7 @@ macro_rules! impl_serializable {
             fn deserialize(
                 buf: &GenericArray<u8, Self::Size>,
             ) -> Result<Self, Self::DeserializationError> {
-                let sz: usize = (<V as SharedValue>::BITS / 8).try_into().unwrap();
+                let sz: usize = <V as Serializable>::Size::USIZE;
                 let mut res = [V::ZERO; $width];
                 for i in 0..$width {
                     res[i] = V::deserialize(GenericArray::from_slice(&buf[sz * i..sz * (i + 1)]))?;
@@ -390,6 +390,7 @@ mod test {
     };
 
     use super::*;
+    use crate::ff::boolean_array::BA3;
 
     impl<V: SharedValue, const N: usize> Arbitrary for StdArray<V, N>
     where
@@ -483,6 +484,13 @@ mod test {
             let copy = StdArray::<Fp32BitPrime, 32>::from_iter(iter);
             assert_eq!(copy, a);
         }
+
+        #[test]
+        fn serde(a: StdArray<BA3, 32>) {
+            let mut buf = GenericArray::default();
+            a.serialize(&mut buf);
+            assert_eq!(a, StdArray::deserialize(&buf).unwrap());
+        }
     }
 
     #[test]