Add ToBytes and FromBytes for u128 (#94)

* add the to and from bytes for u128

* update the CHANGELOG

CHANGELOG.md

@@ -17,7 +17,7 @@
 - #31 (ark-ec) Speedup point doubling on twisted edwards curves
 - #35 (ark-ff) Implement `ToConstraintField` for `bool`
 - #48 (ark-ff) Speedup `sqrt` on `QuadExtField`
-
+- #94 (ark-ff) Implement `ToBytes` and `FromBytes` for `u128`
 
 ### Bug fixes
 - #36 (ark-ec) In Short-Weierstrass curves, include an infinity bit in `ToConstraintField`.

ff/src/bytes.rs

@@ -100,6 +100,29 @@ macro_rules! array_bytes {
                 Ok(res)
             }
         }
+
+        impl ToBytes for [u128; $N] {
+            #[inline]
+            fn write<W: Write>(&self, mut writer: W) -> IoResult<()> {
+                for num in self {
+                    writer.write_all(&num.to_le_bytes())?;
+                }
+                Ok(())
+            }
+        }
+
+        impl FromBytes for [u128; $N] {
+            #[inline]
+            fn read<R: Read>(mut reader: R) -> IoResult<Self> {
+                let mut res = [0u128; $N];
+                for num in res.iter_mut() {
+                    let mut bytes = [0u8; 16];
+                    reader.read_exact(&mut bytes)?;
+                    *num = u128::from_le_bytes(bytes);
+                }
+                Ok(res)
+            }
+        }
     };
 }
 
@@ -225,6 +248,22 @@ impl FromBytes for u64 {
     }
 }
 
+impl ToBytes for u128 {
+    #[inline]
+    fn write<W: Write>(&self, mut writer: W) -> IoResult<()> {
+        writer.write_all(&self.to_le_bytes())
+    }
+}
+
+impl FromBytes for u128 {
+    #[inline]
+    fn read<R: Read>(mut reader: R) -> IoResult<Self> {
+        let mut bytes = [0u8; 16];
+        reader.read_exact(&mut bytes)?;
+        Ok(u128::from_le_bytes(bytes))
+    }
+}
+
 impl ToBytes for () {
     #[inline]
     fn write<W: Write>(&self, _writer: W) -> IoResult<()> {