Remove EmptyFlags construction checks

ff/src/const_helpers.rs

@@ -82,7 +82,7 @@ impl<const N: usize> IndexMut<usize> for MulBuffer<N> {
     }
 }
 
-/// A buffer to hold values of size 2 * N. This is mostly
+/// A buffer to hold values of size 8 * N + 1 bytes. This is mostly
 /// a hack that's necessary until `generic_const_exprs` is stable.
 #[derive(Copy, Clone)]
 #[repr(C, align(1))]

ff/src/fields/models/fp/mod.rs

@@ -638,9 +638,8 @@ impl<P: FpConfig<N>, const N: usize> CanonicalDeserializeWithFlags for Fp<P, N>
             return Err(SerializationError::NotEnoughSpace);
         }
         // Calculate the number of bytes required to represent a field element
-        // serialized with `flags`. If `F::BIT_SIZE < 8`,
-        // this is at most `$byte_size + 1`
-        let output_byte_size = buffer_byte_size(Self::MODULUS_BIT_SIZE as usize + F::BIT_SIZE);
+        // serialized with `flags`.
+        let output_byte_size = Self::zero().serialized_size_with_flags::<F>();
 
         let mut masked_bytes = crate::const_helpers::SerBuffer::zeroed();
         masked_bytes.read_exact_up_to(reader, output_byte_size)?;

serialize/src/flags.rs

@@ -52,12 +52,8 @@ impl Flags for EmptyFlags {
     }
 
     #[inline]
-    fn from_u8(value: u8) -> Option<Self> {
-        if (value >> 7) == 0 {
-            Some(EmptyFlags)
-        } else {
-            None
-        }
+    fn from_u8(_: u8) -> Option<Self> {
+        Some(EmptyFlags)
     }
 }
 

test-templates/src/lib.rs

@@ -593,6 +593,8 @@ macro_rules! generate_field_serialization_test {
                 let b: Fq = rng.gen();
 
                 let byte_size = a.serialized_size();
+                let (_, buffer_size) = buffer_bit_byte_size(Fr::MODULUS_BIT_SIZE as usize);
+                assert_eq!(byte_size, buffer_size);
                 field_serialization_test::<Fr>(byte_size);
 
                 let byte_size = b.serialized_size();