add optional arbitrary impls

Cargo.toml

@@ -13,12 +13,19 @@ repository = "https://github.com/zkcrypto/jubjub"
 version = "0.10.0"
 edition = "2021"
 
+[dependencies.arbitrary]
+version = "1.3"
+features = ["derive"]
+optional = true
+
 [dependencies.bitvec]
 version = "1"
 default-features = false
 
 [dependencies.bls12_381]
-version = "0.8"
+# upstreamed in https://github.com/zkcrypto/bls12_381/pull/138
+git = "https://github.com/heliaxdev/bls12_381.git"
+rev = "d96b104d0dc035af160fd6505e967cb37a553320"
 default-features = false
 
 [dependencies.ff]
@@ -49,6 +56,7 @@ default-features = false
 default = ["alloc", "bits"]
 alloc = ["ff/alloc", "group/alloc"]
 bits = ["ff/bits"]
+arbitrary = ["dep:arbitrary", "bls12_381/arbitrary"]
 
 [[bench]]
 name = "fq_bench"

rust-toolchain.toml

@@ -1,3 +1,3 @@
 [toolchain]
-channel = "1.56.0"
+channel = "1.63.0"
 components = [ "clippy", "rustfmt" ]

src/fr.rs

@@ -19,6 +19,7 @@ use crate::util::{adc, mac, sbb};
 // The internal representation of this type is four 64-bit unsigned
 // integers in little-endian order. Elements of Fr are always in
 // Montgomery form; i.e., Fr(a) = aR mod r, with R = 2^256.
+#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 #[derive(Clone, Copy, Eq)]
 pub struct Fr(pub(crate) [u64; 4]);
 

src/lib.rs

@@ -16,7 +16,7 @@
 //!
 //! This crate uses the `subtle` crate to perform constant-time operations.
 
-#![no_std]
+#![cfg_attr(not(feature = "arbitrary"), no_std)]
 // Catch documentation errors caused by code changes.
 #![deny(rustdoc::broken_intra_doc_links)]
 #![deny(missing_debug_implementations)]
@@ -135,15 +135,26 @@ impl ConditionallySelectable for AffinePoint {
 /// * Add it to an `ExtendedPoint`, `AffineNielsPoint` or `ExtendedNielsPoint`.
 /// * Double it using `double()`.
 /// * Compare it with another extended point using `PartialEq` or `ct_eq()`.
+#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 #[derive(Clone, Copy, Debug, Eq)]
 pub struct ExtendedPoint {
     u: Fq,
     v: Fq,
+    #[cfg_attr(feature = "arbitrary", arbitrary(with = arbitrary_non_zero_fq))]
     z: Fq,
     t1: Fq,
     t2: Fq,
 }
 
+#[cfg(feature = "arbitrary")]
+fn arbitrary_non_zero_fq(u: &mut arbitrary::Unstructured) -> arbitrary::Result<Fq> {
+    let raw: Fq = arbitrary::Arbitrary::arbitrary(u)?;
+    if bool::from(raw.is_zero()) {
+        return Err(arbitrary::Error::IncorrectFormat);
+    }
+    Ok(raw)
+}
+
 impl fmt::Display for ExtendedPoint {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "{:?}", self)
@@ -1118,6 +1129,7 @@ impl_binops_multiplicative_mixed!(AffinePoint, Fr, ExtendedPoint);
 
 /// This represents a point in the prime-order subgroup of Jubjub, in extended
 /// coordinates.
+#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 #[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
 pub struct SubgroupPoint(ExtendedPoint);